ALLEN'S 
COMMERCIAL  ORGANIC  ANALYSIS 


VOLUME 


CONTRIBUTORS 

TO  VOLUME  I 


E.  FRANKLAND  ARMSTRONG,  D.  sc.,  PH.  D.,  A.  c.  G.  i.,  Reading,  England 

JULIAN  L.  BAKER,  F.  i.  c.,  Staines,  England. 

WILLIAM  A.  DAVIS,  B.  sc.,  A.  c.  G.  i.,  Bromley,  England. 

G.  C.  JONES,  F.  i.  c.,  London. 

HENRY  LEFFMANN,  M.  A.,  M.D.,  Philadelphia. 

EMIL  SCHLICHTING,  New  York. 

R.  W.  SINDALL,  F.  c.  s.,  London. 


ALLEN'S  COMMERCIAL 

ORGANIC  ANALYSIS 

A  TREATISE  ON 

THE  PROPERTIES,  MODES  OF  ASSAYING,  AND  PROXIMATE 
ANALYTICAL    EXAMINATION    OF    THE    VARIOUS 
ORGANIC  CHEMICALS  AND  PRODUCTS 
EMPLOYED  IN  THE  ARTS,  MANU- 
FACTURES, MEDICINE,  Etc. 

WITH'  CONCISE  METHODS  FOR 


THE  DETECTION  AND  ESTIMATION  OF  THEIR  IMPURITIES. 
ADULTERATIONS,  AND  PRODUCTS  OF  DECOMPOSITION 

VOLUME  I 

Introduction,  Alcohols,  Yeast,  Malt  Liquors  and  Malt,  Wines  and  Spirits,  Neutral 

Alcoholic  Derivatives,  Sugars,  Starch  and  its  Isomerides,  Paper  and 

Paper-making  Materials,  Vegetable  Acids 

BY  THE  EDITORS  AND  THE  FOLLOWING  CONTRIBUTORS 

E.  F.  ARMSTRONG,  J.  L.  BAKER,  G.  C.  JONES, 

E.  SCHLICHTING     and     R.  W.  SINDALL 


FOURTH  EDITION.     ENTIRELY  REWRITTEN 


EDITED  BY 

HENRY  LEFFMANN,  M.A.,  M.D.,  and  W.  A.  DAVIS,  B.Sc.,  A. C.G.I. 

PROFESSOR  OF  CHEMISTRY  AND  TOXICOLOGY  FORMERLY  LECTURER  AND  ASSISTANT  IN  THE 

IN  THE  WOMAN'S  MEDICAL  COLLEGE  OF  CHEMICAL  RESEARCH  LABORATORY,  CITY 

PENNSYLVANIA  AND  IN  THE  WAGNER  AND    GUILDS    COLLEGE,    IMPERIAL 

FREE  INSTITUTE  OF  SCIENCE,  COLLEGE    OF    SCIENCE    AND 

PHILADELPHIA  TECHNOLOGY,  LONDON 


PHILADELPHIA 
P.   BLAKISTON'S  SON   &  CO. 

1012  WALNUT  STREET 
1909, 

OF    THE 

UNIVERSITY 

OF 


C 


COPYRIGHT,  1909,  BY  P.  BLAKISTON'S  SON  &  Co. 

Registered  at  Stationers'  Hall,  London,  England. 


C\ 


Printed  in  America. 


PREFACE  TO  FOURTH  EDITION. 


SIXCE  the  publication  of  the  third  edition  of  this  work,  the  subject 
matter  of  organic  chemistry  has  been  so  much  extended  that,  in  is- 
suing a  new  edition,  it  has  been  necessary  to  allot  the  revision  to 
specialists,  each  entrusted  with  the  task  of  bringing  a  particular  sec- 
tion up  to  date.  This  is,  indeed,  -the  plan  that  the  distinguished 
author  of  the  work  had  in  view  during  the  latter  years  of  his  life 
when  the  question  of  revision  was  pressing  upon  him. 

Under  this  arrangement,  the  work  has  been  almost  entirely  re- 
written so  that  practically  only  the  general  plan  of  the  earlier  editions 
has  been  retained.  Much  descriptive  matter  now  fully  treated  in 
text-books  on  chemistry  and  technology  has  been  omitted,  the  object 
being  to  Jimit  the  work  to  its  specific  field  of  "  Commercial  Organic 
Analysis."  It  has  been  necessary  to  make  some  changes  in  the  dis- 
tribution of  topics.  Examination  of  Malt  has  been  transferred  to  the 
section  on  Malt  Liquors.  The  subject  of  Cellulose  Nitrates  has  been 
transferred  to  the  section  on  Smokeless  Explosives,  being  included  in 
the  revised  Volume  II.  Special  articles  on  Yeast  and  on  Paper  and 
Paper-making  Materials  have  been  added  to  the  present  volume.  A  uni- 
form system  of  nomenclature  and  abbreviations  has  been  established 
and  will  be  followed  throughout  the  work.  The  decimal  system  of 
weights  and  measures  will  be  used,  except  when  special  conditions 
render  other  standards  necessary.  Unless  otherwise  stated,  all  tem- 
peratures are  centigrade  and  all  readings  of  scale  and  arc  positive. 

By  the  selection  of  contributors  from  both  sides  of  the  Atlantic, 
the  work  has  been  made  more  distinctly  international  and  thus  better 
adapted  to  its  wide  field  of  usefulness.  The  editors,  appreciating 
deeply  the  honour  of  directing  the  revision  of  a  work  that  since  its 
appearance  has  been  in  the  front  rank  of  authorities  in  the  chemical 
laboratory,  have  endeavoured  to  be  worthy  of  the  task  and  of  the  co- 
operauon  of  the  contributors,  and  hope  that  the  revised  edition  will 
maintain  the  reputation  of  the  work  as  the  most  comprehensive  and 
most  representative  treatise  on  '''Commercial  Organic  Analysis"  in 
any  language. 

NOVEMBER,  1909. 

vii 


196408 


CONTENTS. 


INTRODUCTION. 

By  WILLIAM  A.  DAVIS. 

Preliminary  Examination,  3;  Specific  Gravity,  4;  Changes  in  Physical 
State,  16;  Optical  Properties,  22;  Spectrometers  and  Spectrographs, 
33;  Polarimeters,  41;  Arrangements  for  Maintaining  Known 
Constant  Temperature,  53;  Ultimate  Analysis,  57;  Moisture, 
Crude  Fibre  and  Ash,  64;  Action  of  Solvents,  76. 

ALCOHOLS. 
By  G.  C.  JONES 

Methyl  Alcohol,  85;  Wood,  Naphtha,  Wood  Spirit,  99;  Ethyl  Alco- 
hol, no. 

MALT  AND  MALT  LIQUORS. 

By  JULIAN  L.  BAKER. 
Malt,  133;  Malt  Substitutes,  143;  Malt  Extract,  145;  Beer  and  Ale,  149. 

WINES  AND  POTABLE  SPIRITS. 
By  G.  C.  JONES. 

Wines,  165;  Cider,  187;  Potable  Spirits,  187. 

YEAST. 

By  EMIL  SCHLICHTING. 
Yeast,  205;  Pure  Culture  Yeasts,  216;  Compressed  Yeast,  219. 

NEUTRAL  ALCOHOLIC  DERIVATIVES. 
By  HENRY  LEFFMANN. 

Ether,  227;  Esters,  231;  Aldehydes,  253;  Derivatives  of  Aldehydes,  268. 

ix 


X  CONTENTS. 

SUGARS. 
By  E.  FRANKLAND  ARMSTRONG. 

Classification,  285;  Synopsis  of  Properties,  287,  288;  General  Analytic 
Methods,  296;  Sucrose,  338;  Maltose,  361;  Lactose,  365;  Glucoses, 
372;  Honey,  383;  Maple  Products,  388;  Glucosides,  391;  Diabetic 
Urine,  393;  Pentoses,  400. 

STARCH  AND   ISOMERS. 
By  E.  FRANKLAND  ARMSTRONG. 

Starch,  405,  407;  Dextrin,  427;  Cellulose,  429;  Agar-agar,  437;  Gums, 
438;  Proximate  Analysis  of  Plants,  445;  Cereals,  450;  Flour,  453; 
Bread,  458;  Mixed  Flours,  461. 

PAPER  AND  PAPER-MAKING  MATERIALS. 

By  R.  W.  SINDALL. 
Paper,  465;  Physical  Properties,  467;  Wood  Pulp,  480. 

ACID  DERIVATIVES  OF  ALCOHOLS. 
By  HENRY  LEFFMAN. 

General  Reactions,  485;  Acetic  Acid,  488;  Vinegar,  495;  Homologues 
of  Acetic  Acid,  514;  Oxalic  Acid,  527;  Succinic  Acid,  531;  Malic 
Acid,  533;  Tartaric  Acid,  536;  Citric  Acid,  555. 

APPENDIX. 
Detection  of  Lead,  569. 

INDEX.  57 : 


INTRODUCTION. 


BY  WILLIAM  A.  DAVIS,   B.  Sc.,  A.  C.  G.  I. 

THE  term  Analysis,  though  originally  meaning  the  separation  or 
splitting  up  of  a  substance  into  its  constituent  parts,  has  now  become 
greatly  extended  in  its  application,  so  that  a  process  of  chemical 
analysis  may  mean  either 

A  true  analysis,  or  separation  of  a  substance  into  its  constituent 
parts; 

A  qualitative  identification  or  recognition  of  a  substance  sought 
for;  or 

A  quantitative  estimation  made  with  more  or  less  accuracy  of  the 
composition  of  a  substance. 

When  the  quantitative  analysis  is  limited  to  one  or  two  important 
substances  which  constitute  the  valuable  or  active  constituents  of 
a  more  complex  material,  the  analytical  process  is  frequently  called 
an  assay.  It  is  in  this  sense  the  term  assay  is  employed  throughout 
this  work. 

Very  frequently  the  chemical  examination  of  a  substance  includes 
the  search  for,  or  estimation  of,  impurities  and  foreign  constituents 
accidentally  present  or  purposely  added.  The  nature  of  the  foreign 
ingredients  will,  of  course,  largely  depend  upon  that  of  the  substance, 
and  cannot  be  generally  described.  They  may,  however,  be  con- 
veniently classified  under  the  following  heads : 

Foreign  substances  naturally  associated  with  the  main  substance, 
and  not  readily  removed  during  the  process  of  preparation.  Examples: 
acetone  in  wood  spirit;  hydrogen  cyanide  in  bitter-almond  oil,  and 
cresylic  acid  in  carbolic  acid. 

Foreign  substances  introduced  during  the  process  of  manufacture, 
and  not  subsequently  (perfectly)  eliminated.  Examples:  potassium 
cyanate  and  carbonate  in  commercial  cyanide;  sulphuric  acid  and 
lead  salts  in  organic  acids;  alcohol  in  ether. 

Foreign  substances  legitimately  added  in  small  quantity,  to  confer 
some  special  property  on  the  main  substance.  Examples:  mineral 
acids  in  hydrocyanic  acid;  alcohol  in  chloroform. 

I 


2  INTRODUCTION. 

Foreign  substances  produced  by  the  spontaneous  change  of  the 
main  substance.  Examples:  benzoic  acid  in  bitter-almond  oil;  metalde- 
hyde  in  aldehyde;  ethyl  acetate  in  tincture  of  iron  acetate. 

Adulterants  purposely  added  to  increase  the  weight  or  bulk,  to 
confer  some  special  property,  or  to  conceal  weakness  or  inferiority  of 
the  main  substance.  Examples:  water  in  spirituous  and  vinous 
liquids;  tartaric  acid  in  citric  acid;  nitrobenzene  in  bitter-almond  oil. 
In  the  physical  and  chemical  examination  of  organic  materials 
many  methods  are  employed,  the  details  of  which  will  be  given  under 
the  proper  heads,  but  the  following  general  principles  are  frequently 
employed  for  the  recognition  and  quantitative  examination  of  such 
substances. 

A  preliminary  examination  of  the  leading  characters  of  the  sub- 
stance, such  as  its  colour,  taste,  odour,  microscopic  appearance  and 
crystalline  form. 

A  determination  of  the  relative  density  of  the  substance,  some- 
times in  the  solid  form,  more  frequently  in  the  liquid  condition,  and 
occasionally  in  the  state  of  vapour.  The  density  of  the  solution  of  a 
substance  is  often  a  character  of  value. 

Observations  and  operations  connected  with  a  change  in  the  physical 
state  of  the  substance,  such  as  determinations  of  its  melting  and  boiling 
points,  and  its  behaviour  on  distillation. 

A  study  of  the  optical  properties  of  the  substance,  including  its  re- 
fractive and  dispersive  powers,  absorption-spectrum,  fluorescence, 
and  action  on  a  ray  of  polarised  light. 

A  determination  of  the  ultimate  or  elementary  composition  of  the  body. 
The  behaviour  of  the  substance  with  ordinary  solvents. 
The  behaviour  of  the  substance  with  other  reagents. 
An  examination  of  the  substance  for  inorganic  impurities. 
The  foregoing  methods  of  examination  are  chiefly  applicable  to  the 
recognition   of   comparatively   pure   compounds,    but   the   principles 
involved  are  continually  applied  in  the  practical  proximate  analysis 
and   chemical   examination   of   organic    materials.     Thus,   from   the 
behaviour  of  the  associated  substances,  when  examined  by  one  or  more 
of  the  above  methods,  a  practical  recognition,  determination,  or  sepa- 
ration of  the  constituents  of  the  sample  is  effected. 

It  is  not  proposed  to  describe  the  whole  of  the  above  methods  of 
examination  in  detail,  as  many  of  them  are  processes  with  the  general 
nature  of  which  the  user  of  this  book  is  presumably  acquainted.  In 


PRELIMINARY    EXAMINATION.  3 

most  cases  the  outline  of  the  method  of  examination  is  alone  indi- 
cated, but  exceptions  are  made  in  cases  in.  which  the  same  methods 
are  not  in  general  use  in  the  analysis  of  inorganic  substances.  Suffi- 
cient working  details  for  the  use  of  any  one  versed  in  simple  chemical 
manipulation  are  given  under  the  special  articles  devoted  to  the  ex- 
amination of  the  various  organic  preparations  employed  in  commerce. 

PRELIMINARY  EXAMINATION. 

When  the  organic  subsance  to  be  examined  is  of  wholly  unknown 
nature  a  judicious  preliminary  examination  will  often  throw  much  light 
on  its  composition.  The  following  points  should  not  be  lost  sight  of: 

Colour. — The  colours  of  organic  bodies  are  not,  as  a  rule,  very  char- 
acteristic, but  there  are  some  very  remarkable  exceptions.  As  a  rule, 
blue  vegetable  colouring  matters  are  rendered  red  by  acids,  and  the 
blue  colour  is  restored  or  changed  to  green  by  ammonia.  Indigo  is  not 
affected.  Vegetable  yellows  are  generally  turned  brown  by  alkalies, 
and  the  colours  restored  by  acids.  The  examination  of  the  absorption- 
spectra  of  coloured  organic  substances  often  furnishes  most  valuable 
information  (see  page  33). 

Taste. — This  character  must  be  observed  with  extreme  caution,  as 
many  organic  compounds  are  intensely  poisonous.  The  safest  way  is 
to  make  a  weak  aqueous  or  alcoholic  solution  of  the  substance  and 
taste  a  drop  of  the  liquid  cautiously.  Acids  are,  as  a  rule,  sour  or 
astringent  in  taste.  Alkaloids  are  usually  bitter.  The  sugars  and 
glycerin  are  sweet. 

Odour. — The  odour  of  organic  compounds  is  often  highly  character- 
istic, and  notably  so  in  the  case  of  the  neutral  alcoholic  derivatives. 

Microscopic  Appearance. — In  the  case  of  solid  bodies  an  examina- 
tion under  the  microscope  is  often  extremely  useful.  As  a  rule,  the 
use  of  a  high  power  is  neither  necessary  nor  desirable.  The  micro- 
polariscope  affords  a  valuable  means  of  identifying  starches. 

Crystalline  Form. — This  character  is  often  of  great  service  for 
the  recognition  of  organic  substances  and  especially  as  a  test  for  purity. 
In  the  great  majority  of  cases  the  crystals  are  too  small  or  indistinct 
to  admit  of  any  goniometric  determination,  but  the  appearance  of  a 
substance  under  the  microscope  and  especially  its  behaviour  towards 
polarised  light  afford  valuable  evidence.  Instances  of  the  value  of  crys- 
talline form  as  means  of  identification  are  to  be  found  in  the  cases  of 


4  INTRODUCTION. 

cholesterol,  salicylic  acid,  tartaric  acid,  and  some  of  the  alkaloids  and 
their  salts. 

Effect  of  Heat. — The  behaviour  of  organic  substances  on  heating 
is  often  highly  characteristic.  Solids  should  be  heated  in  a  small,  dry 
test-tube.  It  is  well  to  make  an  experiment  first  on  a  piece  9f  platinum 
foil,  as  a  few  substances  explode  violently  when  heated.  On  ignition 
in  the  air  all  organic  substances  other  than  those  conta  ning  metals  are 
completely  consumed.  Sometimes  volatilisation  occurs  without  dark- 
ening; in  other  cases,  a  more  or  less  voluminous  residue  of  carbon  is  left, 
which  is  sometimes  burned  away  only  with  great  difficulty.  Salts 
of  organic  acids  containing  metals  of  the  alkalies  or  alkaline  earths 
usually  leave  these  metals  as  carbonates  on  being  ignited  in  the  air. 
Hence  the  presence  of  carbonate  in  the  ash  indicates  the  previous 
presence  of  an  organic  acid.  Volatile  heavy  metals,  such  as  arsenic 
or  mercury,  are  wholly  driven  off  on  igniting  substances  containing 
them,  but  most  heavy  metals  remain  on  ignition  either  as  oxides  or  in 
the  metallic  state. 

The  specific  gravity,  boiling  and  melting  points,  and  other  physical 
properties  of  the  substance  may  be  roughly  noted  as  part  of  the  prelim- 
inary examination,  but  these  characters  are  referred  to  at  greater 
length  in  the  following  sections. 

SPECIFIC  GRAVITY  OR  RELATIVE  DENSITY 

The  specific  gravity  of  an  organic  solid  or  liquid  is  often  a  most 
valuable  criterion  of  its  identity  or  purity.  Unlike  the  determination 
of  the  density  of  a  vapour,  it  is  frequently  applicable  to  the  accurate 
estimation  of  a  substance  in  solution  or  in  admixture  with  another 
body,  and  in  other  cases  it  miy  be  used  to  discriminate  between  sub- 
stances of  the  same  percentage  composition. 

The  relative  density  of  a  solid  or  liquid  is  generally  referred  to  water 
taken  either  as  unity  or  as  1000.  Both  plans  have  their  advantages, 
and,  as  no  confusion  can  arise  from  such  a  course,  the  sp.  gr.  given  in 
this  work  will  be  stated  in  e  ther  manner,  according  to  convenience  of 
expression  or  comparison. 

The  specific  gravity  bottle  is  the  most  generally  serviceable  means 
of  taking  the  sp.  gr.  of  solids  and  liquids.  It  should  not  be  trusted  to 
contain  the  amount  of  water  marked  on  it,  but  should  be  filled  with 
distilled  water  at  the  temperature  at  which  the  sample  of  liquid  is  to 


SPECIFIC    GRAVITY.  .  5 

be  compared,  and  the  weight  of  contained  water  ascertained.  The 
sp.  gr.  of  the  sample  is  found  by  dividing  the  weight  of  it  which  the 
bottle  contains  by  the  weight  of  water  contained  at  tire  same  tempera- 
ture. When  the  liquid  is  miscible  with  water,  the  wet  bottle  may  be 
rinsed  out  once  or  twice  with  a  few  drops  of  the  sample;  when  the  liquid 
is  immiscible  or  nearly  so  with  water,  the  bottle  should  be  rinsed  once 
or  twice  with  alcohol  and  then  with  ether,  the  last  traces  of  the  latter 
being  got  rid  of  by  a  current  of  dry  air  from  a  bellows,  or  by  sucking  the 
ether-vapour  from  the  warmed  bottle  by  means  of  a  glass  tube. 

The  selection  of  the  temperature  of  15.5°  (60°  F.)  sometimes  in- 
volves consid  rable  practical  inconvenience  especially  in  the  summer 
months.  Squibb  has  introduced  a  urinometer  for  25°  (77° F.)  which, 
in  the  ordinary  use  of  this  instrument,  is  a  much  more  convenient 
temperature.  The  current  United  States  Pharmacopoeia  has  adopted 
this  temperature.  Squibb  has  devised  a  bottle  which  eliminates  the 
inconvenience  of  operating  at  a  special  temperature.  The  annexed 
description  is  from  Ephemeris,  January,  1897. 

The  bottle  (Fig.  i)  should  hold  100  grm.  of  recently-boiled  distilled 
water  at  20°  at  about  58  on  a  scale  of  o  to  100.  In  weighing  the  water 
into  the  bottle,  the  fine  adjustment  to  o.ooi  grm.  is  made 
by  use  of  narrow  strips  of  blotting-paper  that  will  pass 
easily  down  the  bore  of  the  graduated  stem.  When  the 
100  grms.  are  in  the  bottle,  and  the  column  stands  between 
50  and  65  divisions  of  the  scale,  the  stopper  is  put  in,  a 
leaden  ring  is  placed  on  the  neck,  and  the  whole  immersed 
in  a  bath  of  broken  ice  and  water  until  the  column  of 
water  comes  to  rest.  It  should  then  read  at  zero  of  the 
scale,  or  not  much  above  it,  and  the  reading  should  be 
noted.  If  it  reads  below  zero,  the  bottle  is  too  large, 
and  the  stopper  part  of  the  stem  must  be  ground  farther 
into  the  bottle  neck,  until  the  reading,  on  new  trial,  brings 
the  column  a  little  above  zero.  The  bottle  is  then  put 
into  a  bath  at  25°  and  kept  there,  the  bath  being  stirred, — until  the 
column  comes  to  rest,  when  it  should  read  about  90  to  100  of  the 
scale.  Should  it  read  above  100,  while  the  lower  limit  is  as  far 
above  the  zero,  the  bottle  is  too  small,  and  the  end  of  the  stopper  must 
be  ground  off  until  the  reading  of  the  column  is  within  the  gradua- 
tions at  both  ends  of  the  scale. 

With  this  bottle  the  sp.  gr.  can  be  taken  at  any  of  the  temperatures 


INTRODUCTION. 


of  the  standard  unit  volume  to  the  sixth  decimal  place,  but  the  only 
way  to  avoid  confusion  is  to  state  clearly  the  temperature  at  which  the 
mass  of  the  liquid  and  of  water,  respectively,  were  determined.  Thus, 
for  example,  the  sp.  gr.  of  a  substance  expressed  as  1.045  at  2O°/4°, 
means  that  the  value  represents  the  ratio  of  the  density  of  the  substance 
at  20°  to  that  of  water  at  4°.  Compare  on  this  point,  Brown,  Morris  and 
Millar  (Trans.  1897,  71,  77,  note).  For  the  construction  of  a  simple 
thermostat  enabling  the  temperature  to  be  kept  within  a  few  thou- 
sandths of  a  degree  for  long  periods,  see  Lowry,  Trans.,  1905,  87, 
1030,  and  Trans.  Faraday  Soc.,  1907,  part  iii.  A  description  is 
given  on  p.  55. 

SprengePs  Tube. — A  useful  method  of  taking  the  sp.  gr.  of  liquids, 
especially  when  but  small  quantities  are  at  disposal,  is  that  of  Sprengel 


FIG.  2. 


(Jour.  Chem.  Soc.,  1875,  26,  577),  in  which  a  small  U-shaped  apparatus 
terminating  in  horizontal  capillary  tubes  is  substituted  for  the  ordinary 
bottle.  It  may  be  easily  filled  and  the  regulation  of  the  quanity  of  con- 
tained liquid  is  also  easily  effected.  The  results  are  of  a  high  degree 
of  accuracy.  Sprengel's  tube  has  the  advantage  that  it  can  be  used 
for  ascertaining  the  sp.  gr.  at  the  b.  p.  of  water.  It  consists  (Fig.  2) 
essentially  of  a  thin  glass  U-tube  terminating  in  two  capillary  ends 
bent  at  right  angles  and  each  provided  with  a  ground  cap.  One  of 


HYDROMETERS.  7 

these  capillary  tubes  must  have  a  smaller  calibre  than  the  other — not 
larger  than  0.25  mm.  The  larger  tube  should  bear  a  mark  at  m.  The 
tube  is  filled  by  immersing  b  in  the  liquid  under  examination,  connect- 
ing the  smaller  end  with  a  large  glass  bulb,  and  applying  suction  to 
the  latter  by  means  of  a  rubber  tube,  as  shown  in  Fig.  3.  If  now 
the  rubber  tube  be  closed,  the  glass  tube  will  fill  automatically.  It  is 
placed  in  water,  the  ends  being  allowed  to  project,  and  the  water 
is  brought  to  the  proper  temperature.  The  Lowry  thermostat  may 
be  used  here  with  advantage.  A  conical  flask  may  also  be  used  to 
contain  the  water,  the  ends  of  the  Sprengel  tube  being  supported  by 
the  neck.  The  mouth  of  the  flask  should  be  loosely  covered.  As  the 
liquid  expands  in  the  Sprengel  tube  it  will  drop  from  the  larger  orifice. 
When  this  ceases,  the  liquid  is  adjusted  to  the  mark  at  m.  If  beyond 
the  point,  a  little  may  be  extracted  by  means  of  a  roll  of  filter-paper. 
The  tube  is  then  taken  out  of  the  bath,  the  caps  adjusted,  the  whole 
thoroughly  dried,  allowed  to  cool,  and  weighed.  The  same  operation 
having  been  performed  with  distilled  water,  the  calculation  of  the  sp. 
gr.  is  made  as  usual. 

For  more  elaborate  directions  as  to  use  of  this  apparatus  see  Ost- 
wald's  Physico-Chemical  Measurements  or  Findlay's  Practical  Physical 
Chemistry.  For  the  rapid  determination  of  the  sp.  gr.  of  liquids,  espe- 
cially saturated  solutions,  the  Meyerhoffer-Saunders  pipette,  modified 
by  Bousfield,  is  convenient.  (See  Lowry,  Trans.,  1906,  89,  1036.) 

Hydrometers  are  instruments  the  use  of  which  is  too  well  known 
to  require  detailed  description.  Care  should  be  taken  in  making 
accurate  observations  to  read  either  from  the  top,  bottom,  or  centre  of 
the  meniscus,  according  to  the  manner  in  which  the  instrument  is  grad- 
uated. Attention  should  also  be  paid  to  the  temperature  of  the  liquid 
during  the  observation. 

The  graduation  of  hydrometers,  even  when  sold  by  well-known 
firms,  is  often  far  from  accurate;  hence  the  indications  of  such  instru- 
ments should  be  carefully  verified. 

The  accuracy  of  hydrometer-densities  has  been  questioned  in  the 
case  of  milk  and  other  liquids  containing  suspended  particles,  but  the 
experiments  of  L.  Siebold  (Analyst,  1879,  4,  189)  show  that  the  indi- 
cations of  the  hydrometer  in  such  cases  agree  with  those  obtained  by 
the  sp.  gr.  bottle. 

TwaddelPs  hydrometer  is  applicable  only  to  liquids  heavier  than 
water.  The  indications  are  translated  into  actual  sp.  gr.  by  mul- 


INTRODUCTION. 

tiplying  the  degrees  Twaddell  by  5  and  adding  1000.  Thus,  a  liquid 
which  marks  68°  Twaddell  has  an  actual  sp.  gr.  of  (5X68)  +  1000  = 
1340,  compared  with  water  as  1000. 

Baume's  hydrometer  is  not  commonly  used  in  England,  except 
for  ascertaining  the  sp.  gr.  of  saccharine  solutions.  As  originally  con- 
structed, the  point  to  which  the  instrument  sank  when  immersed  in  a 
10%  solution  by  weight  of  common  salt  in  water  was  taken  as  10°.  The 
interval  between  this  point  and  that  at  which  the  hydrometer  stood 
when  immersed  in  pure  water  was  divided  into  10  equal  parts,  and  a 
scale  of  similar  equal  parts  extended  as  far  as  was  necessary.  Baudin 
(Chem.  News,  1870,  54)  found  the  sp.  gr.  of  such  a  solution  to  be  n  n 
at  15°. 

Much  confusion  and  irregularity  exist  as  to  the  scales  of  Baume 
hydrometers  commonly  sold.  C.  F.  Chandler  (Proc.  National  Acad. 
Sci.,  1 88 1,  3)  found  36  different  scales  in  use,  many  of  them  incorrect. 
According  to  Lunge  (Technical  Methods  of  Chemical  Analysis,  trans- 
lated by  Keane,  vol.  i,  part  i,  158  et  seq.),  the  following  formulae  are 
applicable  for  the  conversion  of  Baume  degrees  obtained  by  reference 
to  a  10%  salt  solution  (see  below),  into  sp.  gr.,  n  representing  the 
»  observed  degree. 


Liquids  heavier  than         Liquids  lighter  than 


\vat2r 


water 


At  12.  s 


145-88  -  _     145 


Sp.gr.  -  Sp.gr. 


145.88-;;  135.88  +  w 


At  17.5° 


146.78  c  146.78 


In  a  paper  read  before  the  New  York  Section  of  the  Society  of 
Chemical  Industry  (J .  Soc.  Chem.  Ind.,  1905,  24,  781)  the  chemists 
of  the  laboratory  of  the  (American)  General  Chemical  Company 
use  the  following  formula  for  converting  Baume  degrees  to  sp.  gr. 


HYDROMETERS.  9 

For  liquids  heavier  than  water:  Sp.  gr.  =    *4^      at  60°  F. 

I45~n 

For  liquids  lighter  than  water:    Sp.  gr.  =  —  at  60°  F. 

130+7* 

The  so-called  "rational"  hydrometer,  proposed  originally  by  Kolb 
in  France,  but  most  widely  used  in  Germany,  is  based  on  the  following 
principle: 

If  a  hydrometer  sinks  in  water  to  the  mark  o°,  and  in  a  liquid  D 
having  a  sp.  gr.  d  to  n°,  then,  as  in  each  case  the  weight  of  the  hy- 
drometer W  is  equal  to  the  weight  of  the  liquid  displaced,  we  have  — 
YVt.  of  the  volume  of  water  displaced  by  the  hydrometer  =   W 
\Vt.  of  the  same  volume  of  liquid  D  =dW 

Wt.  of  water  displaced  by  n  divisions  of  the  scale  =n 

Wt.  of  same  volume  of  liquid  D  =dn 

For  the  weights  d\\T  and  W  to  differ  by  nd, 


-n 

Kolb  calibrated  his  hydrometer  by  reference  to  "pure  sulphuric  acid 
of  sp.gr.  1.842  at  15°."  The  point  to  which  the  hydrometer  sank  in 
the  acid  was  indicated  as  66°  Be.  ;  with  this  method  of  calibration,  from 
the  above  formula  (i), 


144.3  -w 

Although  Kolb's  system  of  calibration  was  based  on  an  incorrect 
value  for  the  sp.  gr.  of  pure  sulphuric  acid  (see  Lunge,  op.  cit.), 
(the  sp.  gr.  of  iooc/c  H2SO4  at  15°;'  4°  being  1.8357),  this  method  of 
calibration  has  been  generally  adopted  in  Germany,  and  was  used  for 
a  time  in  the  United  States. 

When  the  Baume  hydrometer  is  calibrated  by  reference  to  a  10% 
solution  of  pure  sodium  chloride  (i  grm.  in  9  grm.  water)  the 
following  formula  is  obtained  at  15°. 


146.3  —n 

This  method  of  calibration  is  known  as  that  of  Gerlach. 

The  Manufacturing  Chemists  Association  of  the  United  States  of 
America  in  1898  adopted  (/.  Soc.  Chem.  Ind.,  1898,  17,45)  another 
method  of  calibration;  in  this  scale  "66°  Be."  refers  to  sulphuric  acid  of 


10 


INTRODUCTION. 


sp.  gr.  1.835  at  i5°/4°  not  because  this  is  the  highest  obtainable 
strength,  but  because  this  is  the  sp.  gr.  of  the  acid  sold  and  handled  as 
"66°  oil  of  vitriol"  in  commerce,  which  contains  93.5%  of  H2SO4  by 
weight. 

TABLE  I. 
Comparison  of  Different  Baume  Hydrometers  with  True  Sp.  Gr.     For  Heavy  Liquids. 


I 

Rational 
Scale 

d  = 
144-3 

Gerlach 
Scale 

d  = 
146.3 

American  Scale 

I 

Rational 
Scale 

d  = 
144-3 

Gerlach 
Scale 

rf- 

146.3 

American  Scale 

d  = 
145 

M.  C.  A. 

at 
i5°/4° 

d  = 
145 

M.  C.  A. 

at 
iS°/4° 

144.3—  n° 
at  15° 

146.3—  M° 

at  15° 

145  —  n° 
at  60°  F. 

144-3—  n° 

at  15° 

146.3  —  n°     145  —  n° 
at  15°       at  60°  P. 

I 

1.007 

I.oo68 

1.007 

.005 

34 

1.308 

•3OI5 

1.306 

•3°9 

2 

1.014 

1.0138 

1.014 

.Oil 

35 

1.320 

•  3131        1-318 

•3*7 

3 

.022 

.0208 

.021 

.023 

36 

*-333 

•3250 

•330 

•334 

4 

.029 

.0280 

.028 

.029 

37 

I-  345 

•337°  I 

•343 

•342 

5 

•037 

•°353 

.036 

.036 

38 

J-357 

•  3494 

•355 

•359 

6 

•045 

.0426 

•043 

•043 

39 

I-37° 

•  36l9 

.368 

•368 

7 

.052 

.0501 

•051 

.050 

40 

1-383 

.3746  i 

.381 

•386 

8 

.060 

.0576 

.058 

•057 

4i 

J-397 

.3876 

•394 

•395 

9 

.067 

•0653 

.066 

.064 

42 

1.410 

.4009 

.408 

•4i3 

10 

•075 

•0731 

.074 

.071 

43 

1.424 

•4134 

.422 

.422 

ii 

.083 

.0810 

.082 

.086 

44 

1.438 

.4281 

.436 

.441 

12 

.091 

.0890 

.090 

•093 

45 

1-453 

•  4421 

•  450 

•451 

13 

.IOO 

.0972 

.098 

.IOO 

46 

1.468 

•4564 

.465 

.470 

14 

.108 

.1054 

.107 

.107 

47 

1.483 

.4710 

.480 

.480 

15 

.116 

.1138 

•US 

.114 

48 

1.498 

.4860 

•495 

.500 

16 

•125 

.1224 

.124 

.122 

49 

I.5I4 

.5012 

.510 

.510 

17 

•134 

.1310 

•133 

.136 

50 

1-530 

•5167 

.526 

•531 

18 

.142 

.1398 

.142 

•143 

51 

1.546 

.5325 

•543 

•  541 

19 

•JS2 

.1487 

•^i 

•*5° 

52 

1  •  563 

•5487 

•559 

.561 

20 

.162 

•1578 

.160 

.158 

53 

1.580 

•5652 

•576 

•573 

21 

.171 

.1670 

.169 

.172 

54 

J-597 

.5820 

593 

•594 

22 

.180 

•T763 

.179 

.179 

55 

1.615 

5993 

.611 

.616 

23 

.190 

.1858 

.188 

.186 

56 

1.634 

.6169 

.629 

.627 

24 

.200 

•!955 

.198 

.201 

57 

1.652 

•6349 

.648 

.650 

25 

.210 

•2053 

.208 

.208 

58 

i  .671 

•^533 

.667 

661 

26 

.220 

•2I53 

.218 

.216 

59 

i  .691 

.6721 

.686 

•683 

27 

.231 

•2254 

.229 

.231 

60 

1.711 

.6914 

.706 

•70S 

28 

.241 

•2357 

•  239 

-238 

61 

1-732 

.7111 

.726  ' 

•727 

29 

.252 

.2462 

.250 

254 

62 

J-753 

•73i3 

•747 

•747 

3° 

.263 

.2569 

.261 

.262 

63 

1.774 

.7520 

.768  ; 

.767 

31 

.274 

.2677 

.272 

.269 

64 

1.796 

•7731 

.790  i 

•793 

32 

.285 

.2788 

.283 

.285 

65 

1.819 

.7948 

.812 

.814 

33 

1.297 

.2901 

•295 

•293 

66 

1.842 

.8171 

.835            .835 

American  Scales. 

i.  Sp.  gr. 


145  - 


at  60°  F. 


See  tables  calculated  by  Emery,  /.  Amer.  Chem.  Soc.,  1899,  21,  117. 


HYDROMETERS.  II 

2.  Manufacturing  Chemists  Association  of  the  U.  S.  A.,  /.  Soc.  Chem. 
Ind.,  1898,  17,  45-1 

The  table  on  page  10  gives  a  comparison  of  the  different  scales  with 
true  sp.  gr.  (at  15°)  for  liquids  heavier  than  water.  As  Gockel  has 
pointed  out  (Zeit.  angew.  Chem.,  1003,  562),  Baume  hydrometers 
should  have  inscribed  on  them  not  only  the  temperature  for  which 
they  are  calibrated,  but  also  the  temperature  of  the  water  used  for 
comparison;  it  should  also  be  stated  whether  the  weights  are  re- 
ferred to  normal  pressure  (760  mm.)  or  to  vacuum.  In  Germany, 
the  Imperial  Commission  of  Normal  Standards  (Kais.  Normal 
Eichungs-Kommission,  1904,  Heft  5)  has  recently  thoroughly  inves- 
tigated the  relation  of  degrees  Baume  ("rational"  scale)  to  true  spe- 
cific gravity.  They  give  the  following  table  (Table  II.)  for  the 
transformation  of  sp.  gr.  at  i5°/4°  into  degrees.  Be.  (rational). 

i  The  scale  adopted  by  the  (American)  Manufacturing  Chemists  Associa- 
tion is  a  most  irrational  one  as  the  values  of  sp.  gr.  plotted  against  degrees  Baume 
do  not  give  a  properly  continuous  curve.  The  non-scientific  character  of  this 
scale  is  at  once  visible  on  considering  the  differences  of  sp.  gr.  for  successive 
degrees  Baume;  e.  g.: 


Degrees  1-2  A  in  sp.  gr.  =  0.006 
2-3  A  in  sp.  gr.  =  0.012 
3-4  A  in  sp.  gr.  =  0.006 


Degrees  10-11  A  =  0.015 
11-12  A  =  0.007 
12-13  A  =  0.007 


4-5      A  m  sp.  gr.    =   0.007 

Degrees  19-20  A   =   0.008 

20-21  A    =   0.014 

21-22  A   =   0.007 
and  so  on. 

In  the  upper  part  of  the  scale  the  differences  are  still  more  peculiar;  e.  g.: 

Degrees  45-46  A   =  0.019 

46-47  A    =   o.oio 

47-48  A    =   0.020 

Degrees  54-55  A   =  0.022 

55-56  A    =   o.on 

56-57  A    =   o.ou 

58-59        A     =     O.O22 

It  would  appear  from  the  statement  in  the  J.  Soc.  Chem.  Ind.,  1905,  24,  782  that 
the  M.  C.  A.  has  now  adopted  the  scale  of  the  (American)  General  ChemLal 
Company  (see  page  8). 


12 


INTRODUCTION. 


TABLE  II. 

Transformation  of  Sp.  Gr.  at  i5°/4°  int°  Degrees  Baume  of  the  Rational  Scale. 


S  15/4         -o           .1           .2 

•3 

-4 

-5           -6 

-7 

Q 

•9 

0.99 

| 

-0.018 

I.  00 

o.i  26'  0.270 

0.414 

o-557 

0.700 

0.843    0.986 

1.128    1.270 

i  .412 

01 

i-553:  1-694    1-835 

1.976    2.117 

2.257    2.397 

2.536    2.675 

2.814 

02 

2-953;  3-°9T    3-229 

3-367!  3-505 

3.643    3.780 

3-9I7I  4-053 

4.189 

°3 

4.3251  4.461    4.596 

4.731!  4-866 

5.0011  5.135 

5.269    5.403 

5-537 

04 

5.671    5.804    5.937 

6.070 

6  .  202 

6.334    6.466 

6.598 

6.729 

6.860 

j.Og 

6.991    7.122 

7.252 

7.382    7.512 

7.642 

7.771 

7.900 

8.029 

8.158 

06 

8.287    8.415    8.543 

8.671 

8.798 

8.9251  9.052 

9.179    9.306 

9-432 

07 

9.558    9.684    9.809 

9-934 

10.059 

10.184 

10.309 

10.433  IO-557 

10.681 

08 

10.805110.929  11.052 

"•175 

T  I  .  298 

ii  .421 

11  -543 

11.665  11.787111.909 

09 

12.030112.  151112.272 

J2-393 

12.514 

12.634 

12-754 

12.87412.994 

13.114 

1.  10 

*3  •  233 

13.35213.471 

I3-590 

13.708 

13.826 

T3-944 

14.062  14.179 

14.296 

II 

14.413114.530  14.647 

14.764 

14.880 

14.996 

15.112 

15.228 

15  .343 

I5-45-8 

12 

15.57315.688115.803 

J5-9I7 

16.031 

16.145 

16.259  16.373  16.486  16.599 

13 

16.712  16.825  16.938 

17.050  17  .162 

17.274 

17.386  17.498  17.610 

17.721 

14 

17.832 

17.943  18.054 

18.164 

18.274 

18.384 

18.494 

18.604 

18.713 

18.822 

I.I5 

18.931 

19.040  19.149 

19.258 

19.366 

19-474 

19.582 

19  .690 

19.798 

J9-905 

16 

20.012 

20.119  20.226 

20.333 

20.439 

20-545 

20.651 

20.757  20.863 

20.969 

i7 

21.074 

21.179  21.284 

21-389 

21-494 

21-599 

21-703 

21  .807  21  .911 

22.015 

18 

22.119 

22.222 

22.325 

22.428 

22.531 

22.63422.737 

22.839  22.941 

23-043 

*9 

23-I45 

23.247 

23-349 

23.45° 

23-55I 

23-652 

23-753 

23-854 

23-955 

24-055 

i  .20 

24-155 

24-255 

24-355 

24.455  24.554 

24-653 

24-752 

24.851 

24.95025.049 

21 

25.148 

25.246 

25.34425.442 

25-540 

25-638 

25-736  25.83425.931  26.028 

22 

26.125  26.222 

26.31926.415 

26.511 

26.607 

26  .  703 

26.79926.895 

26.990 

23 

27.085  27  .180 

27-275!27-37o 

27.465 

27.560 

27.74927.843 

27-937 

24 

28.031 

28.125 

28.219 

28.312^8.405 

28.498 

28.591 

28.684 

28.777 

28.869 

1-25 

28.961 

29-053 

29.145  29.237 

29.329 

29.420 

29.512 

29.603  29.694 

29.785 

26 

29.876  29.967 

30.05830.14930.239 

30-329 

30-4I9 

30-509 

30.59930.688 

27 

30.77730.866 

30.955131.044 

31  .133 

131.222 

3I-3" 

31.400 

31.48831.576 

28 

31.66431.752 

31.84031.92832.015 

32.10232.189 

32.276 

32-363 

32.45° 

29 

32.537  32.624 

32.71132.797 

32.883 

32.969:33.055 

33-141 

33-227 

33-312 

I.30 

33-397 

33.482 

33-567 

33-652 

33-737 

33.82233.907 

33-991 

34-075 

34-159 

31 

34.243  34.327 

34.411(34.495 

34.579;  34.66234.745 

34.828 

34-9" 

34-994 

32 

33 

35-89935-98i 

35-243|35-32535-407 
36.06236.14336.224 

35.48935.571 

136.30536.386 

36.467 

35  -735:35  -817 
36.548:36.628 

34 

36-708 

36.788 

36.86836.948 

37.028 

i37-I07 

37  .187 

37.267 

37-346 

37-425 

j 

1.35 

37-504 

37-  583 

37.662137.741 

37.820 

37.89837.977138.05638.134 

38.212 

36 

38.290 

38.368 

38.446138.524 

38.601 

38  .678  38  .  755  38  .832  38  .909  38  .  986 

37 

39.063 

39-*4o 

39.  217139.  294:39-  37° 

39.44639.522 

39  .  =598  39  .674 

39-750 

38 

39.826 

39.902 

39.978(40.05340.128 

;  40.  203 

40.278 

40.353 

40.428 

40.503 

39 

40.578 

40-653 

40.727 

40.801 

40.875 

40  .  949 

41.023 

41.097 

41.171 

41-245 

i  .40 

41.318 

4L392 

41  .466 

41-539 

41  .612 

41.685 

41.75841.831141  .904 

41-977 

41 

42  .  049 

42.122 

42  .  194  42  .  266  42  .338  42  .410 

42  .482  42  .554^2  .626 

42.698 

HYDROMETERS.  13 

Transformation  of  Sp.  Gr.  at  i5°/4°  into  Degrees  Baume  of  the  Rational  Scale. — Con . 


SiS/4        -o          -i           .2          .3           .4 

-5          -6          -7 

.8          .9 

1.42     42.76942.84042.91242.98343.054 

43.125  43.196 

43.26743.33843.409 

43 

43  -479  43-55°  43  -620  43.69043  .  760 

43.83043.900 

43.97044.04044.110 

44 

44.17944.24844.31844.38744.456 

44.52544.594 

44.66344.73244.801 

1-45 

44.86944.93845.007  45.07545.143 

45.21x45.279 

45-347 

45.41545-483 

46 

45  .551  45  .619  45  .687  45  .  754  45  .821 

45-88845-955 

46.022  46.089  46.156 

47 

46.223  46.29046.357  46-423  46.489 

46.555  46.621  46.687 

46.753  46.819 

48     46.885  46.951  47.017  47.083  47.148 

47.213  47.27947.34447.40947-474 

49     47  •  539  47  -604  47  .  669  47  .  734  47  .  799 

47.86347.928 

47.99248.05648  i-o 

i-5° 

48  .  184  48  .  248  48  .312  48  .376  48  -440 

48.50348.56748.631 

48.69448.757 

51     48.820  48.884  48.947  49.010  49.073  49.136  49.199  49.  262 

49.32549.387 

52     49  .449  49  -512  49  -574  49-636  49  -608  49  •  76°  49  -822-49  .884 

49.94650.008 

53     50.06950.131  50.193  50.25450.315 

50.376  50.437  50.498  50.559  50.620 

54 

50.681  50.742  50.803  50.864  50.924 

50.98451.045  51.105 

51.16551.225 

«.'5S 

51  .285  51  .345  51  .405  51  .46551  .525 

51.58451.643 

5i-703 

51.76351.822 

56 

51.881  51.94051.99952.058  52.117 

52.17652.23552.294 

52-353  52-4ii 

57 

52.469:52.528  52.587  52.645  52-  7°3 

52.761  52.81952.877 

52.93552-993 

58 

53.051  53.10953.16753.225  53.282 

53-33953-397 

53-454 

53-Sii  53-568 

59 

53  -625  53  .682  53  .739  53  .  796:53  .853 

53-90953-966 

54-023 

54.079154.135 

i.  60 

54.191  54.24854.30454.36054.416 

54.47254.528 

54.58454.640154.696 

61 

54-751  54-807  54.863  54.91854.973 

55.02855.08355.138 

55-I9355-248 

62     55  -3°3  55-35855-4I3  55-46855.523  55-57755-63255-687 

55.74255.796 

63     55  -850  55  -9°4  55  -958  56.  012  56.066  56.12056.17456.228 

56.282  56.336 

64 

56.38956.443  56.  497  56.  55°  56.  603] 

56.65656.709 

56-763 

56.81656.869 

1.65 

56.922  56.975  57.028  57.081  57.134 

57.18657.239 

57-292 

57-34457-396 

66 

57.448  57-Soi  57-553  57-6o5  57-657  :57-7°9  57-76i  57-8i3 

57.86557.917 

67 

57.968  58.020  58.072  58.124  58.175  58.226  ^8.278  58.329 

58.38058.431 

68 

58.48258.53358.58458-63558.686  58.73758.78858.839 

58.89058.940 

69 

,58.  990  59.041  59.092  59.142  59-!92 

59.242  59.292:59.342 

59.392  59.442 

1.70 

!59-492  59-542  59-592  59-64I  59-69I 

59.741  59-791 

59-840 

59.89059.939 

71 

59.988  60.038  60.087  60.136  60.185 

60.234  60.283  60.332  60.381  60.430 

72 

60.478  60.527  60.576  60.625  60.673  60.721  60.770  60.818  60.866  60.914 

73 

60.962  6  1  .010  61  .058  61  .106  61  .154 

61  .202  61  .250  61  .298  61  .346  61  .394 

74 

61  .441  61  .489  61  .537  61  .585  61  .632 

61.67961.727  61.77461.821  61.868 

i-75 

61.915  61.962  62.00962.05662.103 

62.15062.197  62.244 

62.291  62.337 

76 

62.383  62.430  62.477  62  .523  62.569  62.615  62.662  62.708  62.754  62.800 

77 

62.846  62.892  62.938  62.984  63  .030  63.075  63  .121  63  .167 

63.21363.258 

78 

63  -3°3  63  -349  63  -395  63  .440  63  .485  63  .530  63  .576  63  .621 

63  .666  63  .711 

79 

63-75663.801  63.84663.891  63.936  63.98064.025  64.07064.115  64.159 

i.  80 

64  .  203  64  .  248  64  .  293  64  .337  64  .381  64  .425  64  .469  64  .  514  64  .  558  64  .602 

81 

64.646  64.690  64.734  64.778  64.822  64.866  64.910  64.954 

64.998^65.041 

82 

6$  .084  65  .12865  •  X72  65  -  215  65  .  258  65  .301  65  .345  65  .388:65  .431  65  .474 

83 

65  -5T7  65  .560  65  .603  65  .646  65  .689  65  .731  65  .774  65  .817  65  .860  65  .902 

84 

65.944  65  .987  66.030  66.073  66.  115!  [66.  157  66.200  66.242  66.284  66.326 

66.368 


INTRODUCTION. 


Great  care  must  be  exercised  in  expressing  or  interpreting  results  in 
the  Baume  scale  as,  owing  to  the  many  different  systems  in  use,  con- 
fusion may  easily  arise. 

The  values  of  sp.  gr.  corresponding  with  degrees  Baume  in  the  tables 
given  by  the  United  States  Department  of  Agriculture,  Bulletin  No 
65  (1902),  Table  VI,  and  Bulletin  No.  107  (1907),  are  apparently  de- 
grees of  the  rational  scale, 

144-3 


d  = 


144-3  -n 


TABLE  III. 
Comparison  of  Degrees  of  Baume"  Hydrometer  for  Light  Liquids  with  Sp.  Gr. 


2  "2 

<£  5 

Sp.  gr.  = 
140 

Sp.  gr.  = 
146 

(8^ 

Sp.  gr.  = 
140      . 

Sp.  gr.  = 
146 

II 

Sp.  gr.  = 
140 

Sp.  gr.  = 
146 

II 

130  +n 

at  60°  F. 

136  +  n 
at  12.5° 

II 

13°  +  w 
at  60°  F. 

136  +M 

at  12  .5° 

II 

130  +  M 

at  60°  F. 

136  +  n 
at  12.5° 

10 

I  .  OOOO 

I  .  OOOO 

1  27 

0.8917 

0-8957 

44 

o  .  8046 

0.8111 

ii 

0.9929 

0.9932 

28 

0.8861 

0.8902 

45 

o  .  8000 

0.8066 

12 

0.9859 

0.9865 

29 

0.8805 

0.8848 

46 

0-7955 

0.8022 

13 

0.9790 

0-9799 

30 

0.8750 

0-8795 

47 

0.7910 

0.7978 

14 

0.9722 

0-9733 

31 

0.8696 

0.8742 

48 

0.7865 

o-7935 

15 

0-9655 

0.9669 

32 

0.8642 

0.8690 

49 

0.7821 

0.7892 

16 

0.9589 

0.9605 

33 

0.8589 

0-8639 

50 

0.7778 

0.7849 

17 

0.9524 

0-9542 

34 

0-8537 

0.8588 

51 

0-7735 

0.7807 

18 

0-9459 

o  .  9480 

35 

0.8485 

0.8538 

52 

0.7692 

0.7766 

19 

0.9396 

0.9420 

36 

0.8434 

0.8488 

53 

0.7650 

0.7725 

20 

0-9333 

0-9359 

37 

0-8383 

o  .  8439 

54 

0.7609 

0.7684 

21 

0.9272 

0.9299 

38 

0-8333 

0.8391 

55 

0.7568 

0.7643 

22 

0.9211 

0.9241 

39 

0.8284 

o  .  8343 

56 

0.7527 

0.7604 

23 

0.9150 

0.9183 

40 

0.8235 

0.8295 

57 

0.7487 

0-7565 

24 

0.9091 

0.9125 

0.8187 

0.8249 

58 

0.7447 

0.7526 

25 

0.9032 

0.9068 

42 

0.8140 

0.8202 

59 

0.7407 

0.7487 

26 

0.8974 

0.9012    i 

i 

43 

0.8092 

0.8156 

60 

0.7368 

0.7449 

Baume  hydrometers  for  liquids  lighter  than  water  are  graduated  in 
two  ways: 

i.  The  point  to  which  the  spindle  sinks  in  a  solution  of  i  grm.  of 
common  salt  in  9  grm.  of  water  at  12.5°  is  called  o°  and  the  point 
corresponding  with  pure  water  is  called  10°.  The  degrees  so  ob- 
tained are  repeated  throughout  the  scale.  This  graduation  gives: 

145.88 
bp.  gr.  = — -;  or  approximately 


135. 


SP-Sr-=x36 


146 


HYDROMETERS.  1  5 

2.  In  America  (see  tables  given  by  Emery,  loc.  cit.)  tne  divisions  of 
the  scale  are  obtained  from  the  formula: 


The  table  given  on  page  14  summarises  the  results  of  both  methods 
of  graduation. 

Carrier's  Hydrometer.  —  On  this,  22°  corresponds  with  22°  Baume, 
but  above  and  below  this  point  the  degrees  are  diminished  in  the 
ratio  of  16  to  15. 

Beck's  Hydrometer.  —  The  zero  point  corresponds  to  the  sp.  gr. 
of  water  and  30°  to  sp.  gr.  850,  the  scale  being  divided  into  equal  parts 
above  and  below  the  zero  point,  as  far  as  desirable. 

Other  hydrometers  are  described  in  the  section  on  sugars. 

Unfortunately,  much  confusion  has  crept  into  the  mode  of  stating 
sp.  gr.  Thus,  if  a  liquid  be  stated  to  have  a  sp.  gr.  0.7185  at  17.5°, 
there  is  no  certainty  as  to  what  is  intended.  It  may  be  meant  that  a 
bottle  which  holds  100  grm.  of  water  at  17.5°  holds  only  71.85  grm. 
of  the  liquid,  or  the  bottle  may  hold  100  grm.  of  water  at  15.5°  (60°  F.), 
at  15.0°,  at  4°,  or  at  o°.  In  many  instances  it  is  uncertain  whether  the 
recorded  sp.  gr.  refers  to  a  comparison  with  an  equal  volume  of  water  at 
the  same  temperature  as  that  at  which  the  liquid  was  weighed  or  at  any 
one  of  the  temperatures  just  given.  As  a  rule,  when  the  sp.  gr.  of  a 
substance  is  stated  to  have  a  given  value  at  15.5°  (60°  F.),  it  may  be  re- 
garded as  probable  that  the  unit  of  water  was  weighed  at  the  same 
temperature,  but  in  the  other  cases  it  is  not  certain  what  is  meant. 

The  sp.  gr.  of  organic  solids  is  best  taken  by  introducing  some  frag- 
ments or  powrder  into  a  sp.  gr.  bottle  and  ascertaining  the  weight. 
The  bottle  is  next  rilled  with  water,  petroleum,  or  some  liquid  of  known 
density  having  no  solvent  action  on  the  solid  to  be  examined,  and  the 
weight  is  then  again  observed.  The  increase  gives  the  weight  of  con- 
tained liquid,  which  divided  by  its  known*  sp.  gr.,  gives  its  volume. 
This  subtracted  from  the  known  capacity  of  the  bottle  gives  the  volume 
of  the  solid,  which,  divided  into  its  weight,  gives  the  sp.  gr.  com- 
pared with  water  as  unity.  Care  must  be  taken  to  avoid  the  adherence 
of  air-bubbles  to  the  solid.  Agitation  will  generally  suffice  to  remove 
them. 

In  many  cases  the  Blount  or  Schumann  bottle  used  in  the  examination 
of  cement  may  be  with  advantage  employed  with  a  suitable  solvent. 

Hager  has  described  (Analyst,  1876,  4,  206),  a  method  of  ascertaining 


1 6  INTRODUCTION. 

the  sp.  gr.  of  fats  and  similar  bodies,  by  diluting  alcohol  or  strong  am- 
monia with  water  until  suspended  fragments  of  the  substance  remain 
in  equilibrium  in  any  part  of  the  liquid  at  the  standard  temperature. 
The  sp.  gr.  of  the  liquid  is  then  taken,  being  the  same  as  that  of  the 
solid.  This  is  an  adaptation  of  the  well  known  method  used  in  as- 
certaining the  sp.  gr.  of  minerals. 

Vapour-densities. — The  determination  of  the  vapour-density  of  an 
organic  substance  often  furnishes  confirmation  of  its  formula.  In 
all  cases  in  which  decomposition  of  the  substance  does  not  occur, 
the  density  of  the  vapour,  compared  with  that  of  hydrogen  at  the  same 
temperature  and  pressure,  is  one-half  the  molecular  weight. 

The  vapour-density  of  a  volatile  liquid  is  most  rapidly  ascertained 
by  means  of  the  method  devised  by  Victor  Meyer.  The  molecular 
weight  of  a  non-volatile  substance  can  be  ascertained  by  measuring 
the  rise  of  b.  p.  or  depression  of  the  freezing  point  of  a  suitable  solvent 
in  which  a  known  amount  of  the  substance  is  dissolved.  For  details 
of  these  methods  see  any  treatise  on  practical  physical  chemistry;  for 
example,  Ostwald  and  Luther's  Physico-chemical  Measurements  or 
Findlay's  Practical  Physical  Chemistry. 

OBSERVATIONS  OF  CHANGES  OF  PHYSICAL  STATE. 

The  melting  point  of  an  organic  substance  is  best  ascertained 
by  heating  a  little  of  the  substance  in  a  capillary  tube  sealed  at  one  end 
and  about  three  inches  long  and  o.oi  to  0.02  in  diameter;  such  tubes 
are  readily  made  by  drawing  out  a  test-tube  in  a  blow-pipe  flame.  The 
tube  containing  the  substance  is  placed  at  the  side  of  the  bulb  of  a 
thermometer,  so  as  to  adhere  to  it,  and  heated  in  a  small  beaker  of  strong 
sulphuric  acid,  the  temperature  of  which  is  gradually  raised  by  means  of 
a  small  burner  placed  beneath.  In  order  to  make  the  reading  of  the 
m.  p.  as  sharp  as  possible  the  temperature  is  raised  only  very  slowly 
just  before  the  substance  melts.  After  melting,  the  substance  should 
be  allowed  to  solidify  and  the  m.  p.  again  taken.  It  must  be  borne  in 
mind  that  although  a  pure  substance  generally  melts  quite  sharply  at 
a  definite  temperature  (within  0.5°)  the  m.  p.  is  much  lowered  and 
rendered  indefinite  by  the  presence  of  a  small  quantity  of  impurity. 
The  m.  p.  is  only  of  value,  therefore,  in  characterising  a  substance  which 
has  been  carefully  purified. 

The  subliming  point  of  an  organic  body  is  sometimes  an  important 


BOILING    POINT.  17 

characteristic,  but  its  value  depends  much  on  the  manner  of  making  the 
observation.  A.  Wynter  Blyth  recommends  the  following  method: 
A  porcelain  crucible  about  3  ins.  in  diameter  is  nearly  filled  with  mer- 
cury (or,  for  high  temperatures,  fusible  metal).  A  minute  quantity  of 
the  substance  to  be  examined  is  placed  on  a  thin  disc  of  microscopic 
covering  glass,  which  is  floated  on  the  mercury,  and  covered  with  a 
glass  ring  (cut  from  tubing),  on  which  is  placed  a  second  disc  so  as  to 
form  a  closed  shallow  cell.  The  porcelain  crucible  is  placed  on  a  brass 
plate  and  covered  with  a  flask  from  which  the  bottom  has  been  removed. 
This  serves  to  keep  away  currents  of  air  and  supports  the  thermometer, 
which  passes  through  a  cork  in  the  neck,  so  that  the  bulb  is  immersed 
in  the  mercury.  In  the  first  examination  of  a  substance  the  tempera- 
ture is  raised  somewhat  rapidly,  the  upper  disc  being  removed  by 
forceps  and  exchanged  for  a  fresh  disc  at  every  rise  of  20°,  until  the  sub- 
stance is  destroyed.  A  second  determination  is  conducted  more  slowly 
and  the  discs  more  frequently  changed,  while  in  conducting  the  third 
determination  the  heat  is  raised  very  cautiously,  and  the  discs  changed 
every  half  degree  when  the  previously  ascertained  subliming  point  is 
nearly  reached.  Blyth  defines  the  subliming  point  as  the  lowest  tem- 
perature, which,  if  maintained  for  60  seconds,  allows  of  the  formation 
of  the  most  minute  dots,  films,  or  crystals  which  can  be  observed  by  a 
microscopic  power  of  1/4  in. 

The  great  majority  of  subliming  points  given  in  this  work  have  not 
been  determined  in  the  above  exact  manner. 

Boiling  Point. — In  making  this  determination  care  must  be  taken 
that  the  thermometer  bulb  is  slightly  above  the  surface  of  the  liquid, 
which  should  be  caused  to  boil  rapidly.  The  liquid  may  be  contained 
in  a  simple  test-tube  fitted  with  a  cork  carrying  the  thermometer  and  a 
short  open  tube  for  the  escape  of  the  vapour.  A  smalltubulated  flask 
or  retort  may  be  substituted  for  the  test-tube.  When  the  quantity  of 
the  liquid  at  disposal  is  only  small,  the  test-tube  should  be  thin  and 
immersed  in  a  flask  half  filled  with  glycerol,  paraffin,  sulphuric  acid, 
or  other  suitable  liquid.  On  heating  the  contents  of  the  flask,  the 
thermometer  fitted  to  the  test-tube  continues  to  rise  till  the  b.  p.  of  the 
liquid  is  attained,  when  it  remains  stationary  till  the  latter  has  evapo- 
rated. A  very  small  quantity  of  liquid  suffices  for  the  determination 
of  the  b.  p.  in  this  manner. 

For  general  purposes  the  apparatus  of  Berthelot  is  convenient. 
Fig.  4,  from  Traube's  Physico-chemical  Methods,  shows  its  con- 
Vol.  I.— 2 


i8 


INTRODUCTION. 


struction.  The  thermometer  is  enclosed  in  an  outer  tube,  so  that  the 
portion  of  the  scale  to  which  the  mercury  rises  is  immersed  in  the  vapour. 
If  this  be  not  done,  a  correction  must  be  applied  for  the  error  produced 
by  the  cooling  of  the  thermometer  tube.  The  bulb  of  the  thermometer 
does  not  reach  into  the  liquid.  A  few  fragments  of 
pumice-stone  or  broken  clay  pipestem  will  prevent 
bumping.  The  exit-tube  at  the  lower  end  of  the  wide 
tube  connects  with  a  condenser.  The  barometric 
pressure  must  always  be  noted  and  correction  made  for 
the  departure  from  the  standard  pressure,  760  mm.,  by 
the  following  formula: 

B=BZ  +  0.0375  (760—?);  in  which 
B  is  the  b.  p.  at  normal  pressure, 
B1  the  observed  b.  p., 
P  the  observed  pressure  in  mm. 

Distillation  does  not  need  detailed  description.  For 
cooling  the  vapour  some  form  of  Liebig's  condenser  is 
commonly  employed.  A  useful  modification,  by  which 
distillation  can  be  made  at  once  to  succeed  digestion, 
without  rearrangement  of  the  apparatus,  has  been  de- 
scribed by  W.  A.  Shenstone,  (Trans.,  1888,  53,  123). 
Recently  several  types  of  double  surface  condensers 
have  been  devised  with  the  object  of  rendering  the  condensing 
action  more  efficient,  so  that  shorter  condensers  may  be  employed 
than  is  possible  with  the  old  Liebig  type.  The  Cribb  condenser 
is  an  instance  of  such  a  form.  Probably  the  most  convenient  for 
all-round  work  is  Davies'  condenser,  made  by  Messrs.  Gallenkamp, 
of  London. 

Fractional  distillation  is  an  analytical  process  closely  related  to 
the  determination  of  the  boiling  and  subliming  points  of  organic  sub- 
stances; by  repeating  the  process  of  distillation  and  collecting  apart 
the  fractions  which  distil  at  every  small  increase  of  temperature,  very 
perfect  separation  may  sometimes  be  effected. 

When  only  a  small  quantity  of  a  complex  liquid  is  submitted  to 
fractional  distillation,  it  is  better  to  keep  the  bulb  of  the  thermometer 
wholly  immersed  in  the  liquid,  as  the  error  liable  to  be  caused  by  this 
arrangement  is  far  less  than  ensues,  especially  towards  the  end  of  the 
distillation,  from  the  temperature  of  the  residual  liquid  rising  more 


FRACTIONAL    DISTILLATION.  1 9 

rapidly  than  the  thermometer  can  acquire  the  temperature  of  the 
vapour. 

In  conducting  a  fractional  distillation,  it  is  desirable  to  operate  on 
a  known  weight  or  volume  of  the  substance,  and  to  note  the  propor- 
tion of  the  whole  which  passes  over  at  every  few  degress  of  rise  in  the 
temperature  of  the  distilling  liquid.  Details  of  the  precautions  which 
should  be  taken  to  ensure  constant  results  will  be  found  in  the  section 
treating  of  the  assay  of  commercial  benzols. 

Fractional  distillation  is  a  process  of  the  utmost  value  for  effecting 
the  proximate  analysis  of  a  mixture  of  organic  substances  of  different 
b.  p.  Speaking  generally,  the  first  portions  which  distil  will  contain  the 
greater  part  of  the  more  volatile  constituents  of  a  complex  fluid, 
but  the  composition  of  the  distillate  at  various  stages  of  the  process 
depends  on  many  circumstances  besides  the  b.  p.  and  relative  propor- 
tions of  the  constituents  of  the  mixture  operated  upon. 

Wanklyn  showed  that  the  proportion  in  which  the  constituents 
of  a  mixture  pass  over  depends  not  only  on  their  relative  abundance 
in  the  mixture  undergoing  distillation,  and  on  their  respective  vapour- 
tensions  at  the  temperature  of  ebullition,  but  also  on  their  mutual  ad- 
hesion and  on  the  densities  of  their  vapours.  He  found  that,  when 
a  mixture  of  equal  weights  of  two  liquids  of  different  b.  p.  was  distilled, 
the  quantity  of  each  constituent  in  the  distillate  was  proportional 
to  the  product  of  its  vapour-density  and  vapour-tension  at  the  tempera- 
ture of  ebullition  of  the  fraction.  Hence,  in  certain  cases,  the  less 
volatile  of  two  substances  may  pass  over  most  rapidly — that  is,  be 
found  in  largest  quantity  in  the  first  fraction  of  the  distillate.  This  is 
true  of  a  mixture  of  methyl  alcohol  (boiling  at  65.2°)  and  ethyl  iodide 
(boiling  at  72°).  If  the  vapour-tensions  and  vapour-densities,  of  the 
two  liquids  are  inversely  proportional,  the  mixture  will  distil  unchanged. 

M.  C.  Lea  found  that,  on  distilling  a  mixture  of  ethylamine,  diethyl- 
amine,  and  triethylamine  hydrochlorides  with  sodium  hydroxide,  the 
whole  of  the  last  amine,  which  is  the  least  volatile  of  the  three,  was  con- 
tained in  the  first  portions  of  the  distillate,  provided  that  its  propor- 
tion was  not  excessive.  A  similar  anomaly  is  observed  on  distilling 
solutions  of  acetic  acid  and  its  homologues. 

Sometimes  anomalous  results  ensue,  owing  to  the  fact  that  the 
tension  of  the  mixed  vapours  is  never  equal  to  the  sum  of  the  tensions  of 
the  individual  vapours.  Berthelot  found  that  when  a  mixture  of  90.9 
parts  of  carbon  disulphide  (boiling  at  46.6°),  with  9.1  of  alcohol  (boiling 


20  INTRODUCTION. 

at  98.4°),  was  distilled,  it  behaved  as  a  homogeneous  liquid.  If 
either  of  the  constituents  was  present  in  excess  of  the  above  proportion, 
it  remained  in  the  retort  in  an  unmixed  condition  after  the  definite 
mixture  had  distilled  over.  Thorpe,  again,  found  that  a  mixture  of 
equal  volumes  of  methyl  alcohol  and  carbon  tetrachloride  distilled  at  a 
temperature  nearly  10°  lower  than  that  of  the  b.  p.  of  the  most  volatile 
constituent,  and  the  carbon  tetrachloride,  which  has  the  higher  b.  p., 
occurred  most  largely  in  the  first  fractions  of  the  distillate. 

In  cases  where  two  immiscible  liquids  are  distilled  together,  the  b.  p. 
is  the  temperature  at  which  the  sum  of  the  vapour-tensions  is  equal  to 
the  atmospheric  pressure.  Thus  benzene  and  water  distil  together  at 
69.1°,  at  which  temperature  benzene  vapour  has  a  tension  of  533.7 
mm.,  and  .steam  224.2  mm.,  the  sum  of  the  two  being  577.9  mm. 

During  the  past  few  years  the  subject  of  distillation  has  been  ex- 
haustively studied  by  Prof.  Sydney  Young  (see  especially  Trans., 
1895,  679;  1902,  707,  768;  1903,  68,  77;  Young  and  Fortey, 
Trans.,  1902,  717,  739  and  752;  1903,  45).  See  his  treatise  on 
Fractional  Distillation  (Macmillan  &  Co.,  Ltd.,  1903). 

From  a  consideration  of  the  foregoing  facts  it  will  be  evident  that  a 
complete  separation  of  a  complex  liquid  into  its  constituents  is  never 
possible  by  a  single  fractional  distillation,  and  that  in  certain  cases  it 
is  impossible  even  on  repeating  the  operation  a  very  great  number  of 
times. 

A  great  improvement  in  the  practice  of  fractional  distillation  was 
made  by  Warren,  who,  in  his  researches  on  American  petroleum, 
employed  a  Liebig's  condenser  inclined  towards  the  distilling  flask,  and 
kept  at  such  a  temperature  as  to  cause  condensation  of  the  less  volatile 
constituents  of  the  mixed  vapour,  while  those  of  lower  b.  p.  passed  on  to 
a  condenser  kept  cool  in  the  usual  way,  and  inclined  in  a  direction 
opposite  to  the  first. 

Many  arrangements  have  been  devised  by  which  the  vapour  of  the 
distilling  liquid  is  partially  condensed  and  succeeding  portions  are 
caused  to  be  washed  with  the  liquid  produced,  which  periodically  runs 
back  into  the  distilling  flask.  A  very  useful  arrangement  of  this  kind  is 
that  of  Le  Bel  and  Henninger  (Fig.  5)  which  consists  of  a  number  of 
bulbs,  ranging  from  2  to  6,  blown  upon  a  tube,  which  is  fitted  by 
means  of  a  cork  into  the  mouth  of  the  flask  containing  the  liquid  to  be 
distilled.  The  upper  end  of  the  tube  is  furnished  with  an  inclined 
side-tube,  which  can  be  fitted  by  a  cork  to  a  condenser,  and  with  an 


FRACTIONAL    DISTILLATION. 


21 


orifice  through  which  a  thermometer  can  be  passed,  so  as  to  observe 

the  temperature  of  the  vapour  which  passes  over.     Each  of  the  bulbs 

is  connected  with  the  one  below  by  means  of  a 

small  side-tube.      In  the  constriction  of  each 

bulb   is  placed  a  small  cup    of  platinum   or 

copper  gauze,  of  the  size  and  shape  of  a  small 

thimble.     These  cups  are  made  by  folding  the 

gauze  over  the  end  of  a  stout  glass  rod.     The 

ascending  vapour  condenses  in  the  cups,  and 

thus    serves  to  wash  the  vapour  subsequently 

formed,   as  it  bubbles    through.      When    the 

liquid  rises  to  a  certain  height  in  each  bulb  it 

runs  off  by  the  side-tube,  and  ultimately  finds 

its  way  back  to  the  distilling  flask,  the  flame     FlG-  5-  FlG-  6- 

under  which  is  so  regulated  as  to  keep 
all  the  cups  full,  and  cause  the  distillate 
to  fall  from  the  end  of  the  tube  in 
separate  drops.  In  ah  improved  form 
of  dephlegmator,  devised  by  Glynsky 
(Fig.  6),  the  wire  gauze  is  replaced  by 
hollow  balls  of  glass,  introduced  into 
the  bulbs  during  manufacture. 

Hempel  (Zeit.  Anal,  Chem.,  1881,  20, 
502)  substituted  for  the  more  complex 
arrangement  a  long  wide  glass  tube, 
•  arranged  vertically  and  filled  with  solid 
glass  beads.  By  this  contrivance  he 
obtained  alcohol  of  95%  by  slowly  dis- 
tilling spirit  of  18%. 

For  a  comparative  study  of  the  effi- 
ciency of  different  types  of  still-head  see 
a  paper  by  S.  Young  (Trans.,  1899,  75, 
679),  in  which  new  forms  are  also  de- 
scribed. The  types  of  still-head  (made 
by  J.  J.  Griffin  &  Sons,  London)  shown 
in  Fig.  7,  are  very  efficient.  When  a 
substance  decomposes  on  boiling  under 

ordinary  pressure,  it  can  often  be  purified  by  distillation  under  reduced 

pressure.     For  methods  see  Gattermann's  Practical  Methods  of  Organic 


FIG.  7. 


22 


INTRODUCTION. 


Chemistry,   and,  in  greater  detail,  Lassar-Cohn's  Arbeitsmethoden  f. 
organisch-chemische  Laboratorien,  1903. 

OPTICAL  PROPERTIES. 

Refraction  and  Dispersion. — The  refractive  index  of  a  liquid 
is  often  a  valuable  means  of  identification.  The  most  convenient 
instrument  for  accurately  measuring  refractive  indices  is  Pulfrich's 
refractometer  made  by  the  Zeiss  company.  For  detailed  description  and 
instructions  for  use  see  Findlay's  Practical  Physical  Chemistry.  Spe- 
cial types  of  instrument  for  measuring  the  refractive  index  of  butter 
fat,  milk  fat,  or  beer  are  manufactured  by  the  firm  of  Zeiss. 

REFRACTOMETERS. 

As  the  refractometer  is  most  widely  used  in  analysis  in  dealing  with 
fats  and  oils,  the  description  of  the  different  types  of  this  instrument 


FIG.  8. 

will  be' included  in  Volume  II.     A  few  of  the  principal  types  of  refrac 
tometer  are  shown  below. 


REFRACTOMETERS.  23 

Fig.  8  shows  the  Pulfrich  instrument,  made  by  the  Zeiss  company, 
and  used  for  measurements  of  the  refractive  index  of  liquids  and 
solutions.  It  is  fully  described  in  a  pamphlet  issued  by  the  makers  and 
in  most  works  on  elementary  physico-chemical  measurements,  e.  g., 
Findlay's  "Practical  Physical  Chemistry"  (Longmans).  Fig.  9 shows 


FIG.  9. 


the  Abbe  refractometer  which  is  used  for  liquids  having  a  refractive 
index  between  =   1.3  and  1.7. 

In  this  instrument  the  liquid  to  be  tested  is  placed  between  two  simi- 
lar prisms  which  must  be  of  greater  refractive  index  than  the  sample. 
When  light  meets  the  surface  separating  the  lower  prism  from  the  liquid, 
it  is  totally  reflected  if  the  angle  of  incidence  is  greater  than  the  critical 
angle.  Hence,  if  the  double  prism  be  viewed  through  a  telescope  the 


24  INTRODUCTION. 

field  will  be  partly  dark  and  partly  bright.  The  telescope  is  attached 
to  a  sector  bearing  a  scale,  while  the  double  prism  is  connected  with 
an  arm  which  carries  an  index  moving  over  the  divided  scale.  By 
rotating  the  prisms  the  critical  line  dividing  the  field  of  view  can  be 
brought  to  coincidence  with  the  centre  of  the  cross-webs  in  the  eye- 
piece. The  reading  on  the  scale  then  gives  the  index  of  refraction  with- 
out any  calculation. 


FIG.  io. 

-  If  the  light  used  is  not  monochromatic  the  position  of  the  critical  line 
in  the  field  will  vary  for  each  component  colour.  There  will  thus  be  a 
coloured  fringe  dividing  the  two  portions.  In  order  to  annul  this  colour 
disturbance  a  compensator  is  introduced  which  consists  of  two  direct- 
vision  prisms  of  equal  dispersion,  and  can  be  rotated  by  means  of  a 
screw  in  opposite  directions  round  an  axis  parallel  to  the  line  of  vision. 
The  reading  on  the  divided  head  of  the  compensator  when  the  colour 
fringe  is  neutralised  gives  the  dispersion  of  the  liquid  for  the  particular 
light  used. 

Fig.  9  shows  the  form  of  instrument  used  when  it  is  required  to 
maintain  the  test  liquid  at  a  certain  temperature.  The  prisms  are 
mounted  in  metal  boxes,  through  which  a  stream  of  water  at  the 
requisite  temperature  is  passed  from  a  convenient  source.  The  Abbe 


REFRACTOMETERS.  25 

refractometer  with  non-heating  prisms  (Fig.  10)  is  used  in  measuring 
refractive  indices  of  solid  bodies  (e.  g.,  crystals)  and  of  viscous  plastic 
substances.  The  measurements  are  made  by  means  of  either  re- 
flected or  grazing  incident  light.  The  Zeiss  company  supplies  on 
application  a  pamphlet  describing  in  detail  the  construction  and  use  of 
the  Abbe  ref ractometers ;  a  special  pamphlet  giving  a  complete 


•Oc 


FIG.  ii. 

bibliography  of  the  technical  application  of  refractometers  is  also  issued 
by  the  same  firm. 

As  the  Immersion  Refractometer  of  Zeiss  is  now  very  widely  used  in 
commercial  organic  analysis  (for  example,  in  the  estimation  of  alcohol 
in  beers  by  Ackermann's  method;  in  the  examination  of  products 
containing  grape  or  cane  sugar;  in  the  analysis  of  blood  and  exuda- 
tions), a  short  account  may  be  given  of  this  instrument,  which  is 


26 


INTRODUCTION. 


FIG.  12. 


illustrated  in  Fig.  n.  The  method  of  measurement  is  founded  on  the 
observation  of  the  border  line  of  total  reflection  in  a  telescope  as  in  the 
refractometers  mentioned  above,  but  the  manipulation  is  much  more 
simple  than  with  these  instruments.  The  prism 
(Fig.  12)  at  the  lower  end  of  the  refractometer  held 
vertically  is  simply  immersed  in  the  solution  con- 
tained in  a  well-filled  beaker. 

The  prism  body  is  cylindrical  in  shape  (so  that 
awkward  corners  and  indentations  difficult  to  keep 
clean  do  not  exist)  and  only  glass  parts  are  immersed, 
so  that  the  instrument  can  be  used  for  acid  solu- 
tions (for  example,  acetic  acid).  In  using  the  instru- 
ment care  must  be  taken  that  day-  or  lamp-light 
passes  into  the  fluid  parallel  to  the  oblique  prism 
surface,  as  indicated  in  Fig.  13,  which  shows  in 
section  an  old  type  of  the  instrument  now  super- 
seded by  that  of  Fig.  n.  In  the  new  type  of  dip- 
ping instrument,  light  is  reflected  from  the  mirror  below  the  trough. 

The  lower  end  of  the  refractometer  is  immersed  in  the  middlemost  of  the  5 
beakers  of  the  front  row.  The  rectangular  mirror  fitted  under  the  trough  reflects 
the  light  of  the  bright  sky  through  a  glass  plate  upwards  into  the  beaker  and 
through  the  fluid  into  the  refractometer.  The  latter  hangs  by  its  hook  H  upon  the 
wire  frame  T.  Observations  are  made  from  above  by  means  of  the  ocular  Oc. 
The  border  line  of  total  reflection  is  achromatised  by  turning  the  milled  ring  R. 
The  micrometer  screw  Z  gives  one-tenth  scale  divisions. 

Conforming  to  the  new  process  of  observation,  the  instrument 
consists  essentially  of  the  following  parts : 

A  Prism  P  of  hard  glass,  with  a  refracting  angle  of  about  63°. 

A  Telescope,  rigidly  connected  with  the  prism,  formed  by  the  object- 
ive O  and  eye-piece  Oc,  with  the  Scale  Sc  and  Micrometer  Screw  Z  in 

Fig.    12. 

A  Compensator  A,  placed  between  prism  P  and  objective  O,  which 
can  be  rotated  about  the  axis  of  the  telescope  by  means  of  the  milled 
Ring  R. 

The  Border  Line,  which  separates  the  bright  part  of  the  field  from  the 
dark,  is,  on  account  of  the  difference  in  dispersion  between  glass  and 
fluids,  generally  fringed  with  colour  and  quite  unsuitable  for  an  exact 
reading.  On  rotating  the  compensator  by  means  of  the  milled  ring  R 
the  colour  disappears  and  the  separating  line  between  dark  and  light 
becomes  quite  sharp  and  colourless.  The  position  of  this  sharp  line 


REFRACTOMETERS. 


27 


relative  to  the  scale  is  the  measure  of  the  refractive  index  of  the  fluid. 
Table  IV  gives  the  value  of  the  refractive  index  corresponding  with 
each  scale  division.  The  scale  divisions  are  read  directly  and  inter- 
mediate positions  calculated  in  decimals  of  a  division  by  means  of  the 
micrometer  screw  Z,  the  scale  being  slid  across  the  border  line  until 


FIG.  13. 

the  scale  division  previously  noted  stands  contiguous  with  it.  The 
division  on  the  micrometer  drum  then  shows  the  decimal  of  the  scale 
index  on  the  added. 

The  immersion  refractometer  has  a  range  of  measurement  between  a 
refractive  index  nD=  1.325  (sea-water  in  the  tropics)  and  nD  =  1.366 
(alcohol).  Within  this  range  fall  the  refractive  indices  of  aqueous  solu- 
tions of  salts,  acids,  sugars,  and  of  liquids,  such  as  beer  and  wine.  In 


28 


INTRODUCTION. 


spite  of  its  simplicity,  this  refractometer  excels  in  the  accuracy  of  its 
readings  all  other  kinds  of  refractometer,  with  the  exception  of  inter- 
ference refractometers.  It  is  of  course  necessary  that  observations 
should  be  made  at  a  known  temperature,  17.5°  being  the  temperature 
corresponding  with  the  values  in  the  table. 

TABLE  IV. 

Table  for  the  Calculation  of  the  Scale  Divisions  of  the  Immersion  Refractometer  in 
Refractive  Indices  n  u  and  vice  versa. 


Scale 
Divisions 

WD     =     T«3 

Scale 
Divisions 

»D   -  x-3 

—5 
—4 
—3 

.  2 

—  i 

25  39 
25  78 
26.18 
26.57 
26  96 

50 
51 
52 

53 
54 

46.50 

46-87 
47.24 
47.61 
47  98 

Q 

2*7    ^6 

4° 

e< 

Aft    «6 

37 

I 

2 

3 
4 

27  75 
28.14 

28  54 
28  93 

i 

2 

3 

4,0 
8,0 

12,0 

16  o 

56 

11 

59 

4°-ou 
48.73 
49.10 

49  47 
49  84 

i 

2 

3 

3,7 
7-4 
n,  i 
id.  8 

! 

9 

29.32 
29.71 
30.10 
30  49 
30.87 

6 

8 
9 

20,0 
24,0 
28,0 
32,° 
36>° 

60 
61 
62 

63 
64 

50.21 
50.58 
50-95 
5i  32 
51.69 

6 

8 
9 

18,5 

22,2 

25,9 
29,6 

33,3 

10 

n 

12 
13 
14 

31.26 
3i  65 
32.04 
32.42 
32  81 

65 
66 

67 
68 
69 

52.05 
52.42 
52.79 
53.i6 
53  52 

15 

16 
18 

33  20 
33  58 
33  97 

39 

70 

7i 
72 

53  88 
54-25 
54-6i 

36 

19 

34  35 
34  74 

i 

3,9 

73 
74 

54  97 
55  33 

T 

3,6 

20 
21 
22 

23 
24 

35  13 
35  5i 
35  90 
36.28 
36.67 

2 

3 
4 

6 

7,8 
JI»7 
iS,6 
i9,5 

23,4 

3 

77 
78 
79 

55  69 
56.06 
56.42 
56.78 
57  14 

i 

i 

W 

10,8 

14,4 
18,0 

21,6 

25 
20 

27 
28 
29 

37  05 
37  43 
37.8i 
38.20 

38.58 

8 
9 

27,3 
31,2 

35,i 

80 
81 
82 

11 

57  5o 
57-86 
58.22 
58.58 
58  94 

i 

25,2 
28,8 
32,4 

30 

31 
32 

33 

34 

38-96 
39  34 
39  72 
40.  10 
4048 

li 

87 
88 

89 

59  30 
59  66 
60.02 
60.38 
60.74 

REFRACTOMETERS. 


29 


TABLE  IV.— Continued. 


Scale     i               _ 
Divisions  !           D          J  *  •> 

Scale 
Divisions 

»D  -  *-3 

35              40  86 

38 

90 

61.09 

35 

36             41  .24 
37              4i  62 
38              41  99 
39              42  37 

i 

2 

•i 

3,8 
7.6 

114. 

91 
92 

93 
94 

oi  45 
61.81 
62.17 
62  52 

i 

2 
•J 

3,5 
7,o 

IO  ^ 

40              42.75 
4i              43  13 
42              43  50 
43              43  88 
44              44  26 

4 

| 

8 

15,2 
19,0 

22,8 
26,6 
30,4 

9 
3 

99 

62.87 
63  23 
63  59 
63  94 
64  29 

4 
6 
8 

14,0 
17,5 

21,0 

24,5 
28,0 

45              44  63 
46              45  oo 
47              45  37 
48              45  75 
49              46  12 

9 

34,2 

100 

101 
102 
103 
I04 

64.64 
65.00 

65  35 
65.70 
66.05 

9 

31,5 

50              46  50 

105 

66.40 

Example:  Scale  division  3.1  corresponds  to  the  Refractive  Index  «D  =1.32854  + 

0.000039  =  1.32858. 

A  convenient  type  of  water  heater  and  water-pressure  regulator  by 
means  of  which  the  trough  A  is  maintained  at  this  temperature,  is 
shown  in  Fig.  14,  and  is  described  in  detail  in  pamphlets  issued  by 
the  Zeiss  company.  The  arrangement  devised  by  Lowry  for  sup- 
plying water  to  polarimeter  tubes  at  a  definite  temperature  can  also  be 
used  (page  54).  The  description  of  the  Zeiss  heater  is  as  follows: 

The  spiral  heater,  about  3.5  metres  in  length,  of  stout  copper,  is 
enclosed  in  the  space  between  two  telescoping  metal  cylinders.  The 
inner  cylinder  is  provided  with  a  copper  bottom,  through  which  the 
heated  air  generated  by  a  bunsen  burner,  petroleum  or  spirit  lamp  is 
evenly  distributed  and  conducted  to  the  copper  pipe. 

The  top  of  the  spiral  heater  is  connected  with  the  tap  C  of  the 
heating  trough  A  by  a  short  length  of  tightly  stretched  tubing,  which 
should  incline  upwards  in  the  direction  of  C.  In  this  way  the  accumu- 
lation of  air  bubbles,  which  would  otherwise  obstruct  the  uniform  flow 
of  water,  is  checked.  By  means  of  the  tube  D  the  water  is  drained  off 
by  a  glass  or  metal  tube  and  led  to  a  sink.  When  desired,  the  heating 
apparatus  can  be  thrown  out  of  action  by  turning  off  the  gas,  turning 
the  cock  at  C  and  drawing  off  the  water. 

It  is  generally  best  not  to  have  a  too  sluggish  flow  of  water,  and  to 
obtain  a  certain  approximate  temperature  first  by  appropriate  manipu- 
lation of  the  source  of  heat;  the  temperature  is  finally  adjusted  to  the 


INTRODUCTION. 


exact  degree  required,  by  varying  the  difference  in  elevation  between 

the  cistern  A  of  the  water-pressure  regulator  and  the  heating  trough  A. 

The  difference  in  elevation  between  the  cistern  A  and  the  heating 


FIG.  14. 

trough  may  be  varied  in  two  ways:  cistern  A  is  either  suspended  from  a 
cord  running  on  a  roller,  the  free  end  of  which  is  made  fast  as  with 
roller  blinds,  or  it  is  hung  on  two  hooks  driven  into  a  board.  The 


REFRACTOMETERS. 


latter  can  be  made  to  slide  up  and  down  in  a  frame  formed  of  a  board 
about  i  metre  in  length  and  fitted  with  two  strips  placed  lengthwise 
at  the  sides,  the  whole  being  fastened  against  a  wall.  Holes  are  bored 
through  this  board  arranged  in  zig-zag  lines  and  each  about  i  cm. 
above  the  next  lower  one,  the  board  with  cistern  A  being  kept  at  the 
desired  height  by  passing  a  peg  through  one  of  the  holes.  It  is  an  easy 
matter  to  find  by  trial  the  number  of  holes  by  which  the  board  requires 
moving  in  order  to  cause  the  temperature  to  vary  by  i°. 

Manipulation  of  the  Immersion  Refractometer. — It  is  first  neces- 
sary to  see  that  the  instrument  is  properly  adjusted.  For  this  purpose 
the  heating  trough  A  (Fig.  u)  is  placed  with  its  long  side  parallel 
to  the  window  and  the  mirror  turned  towards  a  bright  sky.  The 
trough  is  then  half-filled  with  water  and  a  beaker  filled  with  distilled 
water  is  placed  in  one  of  the  five  holes  in  the  front  row  immediately 
above  the  mirror.  Finally  the  refractometer  is  hung  by  the  hook  H 
upon  the  wire  frame  so  that  the  prism  is  completely  submerged  in  the 
water  contained  in  the  beaker. 

The  whole  apparatus  is  now  allowed  to  stand  for  10  minutes  or  so  to 
bring  everything  to  the  same  temperature.  When  the  distilled  water 
has  exactly  taken  the  temperature  of  the  bath,  the  eyepiece  is  focussed 
on  the  divisions  of  the  scale  by  turning  the  milled  head  of  the  eye-piece 
until  the  lines  and  numbers  are  seen  quite  distinctly,  and  the  mirror 
adjusted  so  that  the  light  of  the  bright  sky  is  seen  directed  through 
the  beaker.  The  upper  part  of  the  field,  from  — 5  to  about  15  appears 
bright  and  is  separated  from  the  lower  dark  part  by  a  sharp  line  of 
demarcation,  if  the  index  on  the  ring  of  the  compensator  stands  at  5. 

TABLE  V. 

The  correctly  adjusted  refractometer  should  show,  for  distilled 
water  at 


Temperature    .    . 

io°C. 

II 

12 

X3 

14 

15 

16 

J7 

I7-S 

18 

I9«c. 

the  Scale  Division 

16-3 

16.15 

16.0 

15-85 

iS-7 

15-5 

15-3 

i5-i 

15-0 

14.9 

J4-7 

Temperature    .    . 

20°  C. 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30°  c. 

the  Scale  Division 

14-5 

14.25 

14.0 

13-75 

13-5 

13-25 

13.0 

12.7 

12.4 

12.  1 

ii.  8 

32  INTRODUCTION. 

The  reading  is  taken  as  already  explained  and  the  temperature  of 
the  distilled  water  noted.  Reference  to  Table  V1  will  show  if  the 
Refractometer  be  correctly  adjusted. 

By  means  of  this  table  it  is  possible  to  test  the  adjustment  of  the  re- 
fractometer  without  having  first  to  adjust  the  bath  to  the  normal 
temperature  of  17.5°.  Should  the  average  of  further  careful  readings 
deviate  from  that  contained  in  Table  V,  the  following  should  be 
resorted  to : 

The  eye-piece  end  of  the  refractometer,  hanging  on  the  wire  frame, 
is  grasped  from  behind  with  the  thumb  and  fore-finger  of  the  left  hand, 
the  micrometer  drum  set  to  10  and  the  steel  point  enclosed  in  the  case 
of  the  apparatus,  inserted  into  one  of  the  holes  of  the  nickelled  cross- 
holed  screw,  lying  on  the  inner  side  of  the  micrometer  drum.  The  point 
is  then  turned  anti-clockwise  (as  seen  from  the  rear)  whereupon  the 
nickelled  milled  nut,  which  governs  the  micrometer,  becomes  loosened. 
The  temperature  of  the  distilled  water  in  the  beaker  is  again  read  to 
ensure  that  it  has  remained  constant  and  then  Table  V,  is  consulted  to 
find  the  "adjusting  number"  properly  belonging  to  the  temperature  in- 
dicated. By  turning  the  point  the  border  line  is  brought  exactly  on 
the  integer  scale  division  belonging  to  the  adjusting  number,  and  the 
still  loose  micrometer  drum  is  turned  so  that  the  index  corresponds  with 
the  decimal  portion  of  the  adjusting  number.  The  drum  is  now  held 
firmly  with  the  thumb  and  fore-finger  of  the  left  hand,  while  the  nut 
is  again  screwed  up  tight  by  the  right  hand,  care  being  taken  that  the 
drum  does  not  wander  off  the  index.  Finally  the  new  adjustment  is 
tested  by  repeated  readings.  After  the  instrument  has  been  properly 
adjusted,  measurements  can  be  made  in  the  manner  already  described, 
using  a  beaker  full  of  the  liquid  to  be  examined.  When  only  small 
quantities  of  the  liquid  are  available  (as,  for  example,  in  dealing  with 
blood  serum)  or  the  solution  is  too  deeply  coloured,  as  in  the  case  of 
dark  beer  or  molasses,  an  auxiliary  prism  is  used,  the  face  of  which 
is  laid  on  the  polished  elliptical  face  of  the  refractometer  prism.  The 
liquid  to  be  examined  is  applied  between  the  two  prism  faces,  which  are 
then  locked  into  position  by  a  suitable  cover.  Details  for  the  use  of 
the  auxiliary  prism  are  supplied  by  the  makers  of  the  instrument. 

When  a  volatile  liquid  or  solution  which  would  quickly  evaporate 

J)  "  Uber  quantitative  Bestimmungen  Wcassriger  Losungen  mit  dem  Zeiss' schen 
Eintauch-Refraktometer."  By  Medizinalassessor,  Dr.  B.  Wagner,  Jena,  1903 
(Diss.),  p.  14. 


SPECTROMETERS  AND  SPECTROGRAPHS. 


33 


has  to  be  examined,  a  metal  beaker  M  in  Fig.  13,  supplied  with  the  in- 
strument, is  used;  it  is  clamped  to  the  prism  of  the  refractometer  by 
means  of  the  bayonet-joint,  and,  while  the  refractometer  is  held  with 
the  prism  pointing  upwards,  it  is  filled  with  the  liquid  to  be  examined. 
The  cap  D  is  then  carefully  fitted  and  locked,  and  the  observation  made 
by  hanging  the  refractometer  in  the  wire  frame  of  the  trough  A,  so 
that  the  metal  beaker  is  submerged  in  the  bath.  If  trough  B  is  used 
(older  type  of  instrument)  the  refractometer  is  inclined  as  shown  in 
Fig.  12. 

SPECTROMETERS  AND  SPECTROGRAPHS. 

The  Absorption-spectrum  of  an  organic  substance  occasionally 
furnishes  information  not  to  be  obtained  in  any  other  way,  and  in  the 
examination  of  blood-stains,  dye  materials,  and  other  coloured  sub- 
stances is  often  of  great  utility. 


FIG.  15. 

Spectrometers  and  Spectrographs.— Probably  the  most  conven- 
ient spectrometer  for  use  in  technical  analysis,  especially  in  the  ob- 
servation of  absorption  spectra,  is  the  Hilger  wave-length  spectrometer 
of  the  constant  deviation  type,  made  by  A.  Hilger,  London,  and  shown 
in  Fig.  15. 

The  prism  is  of  a  special  form  (Fig.  16)  and  may  be  considered  as 
built  up  of  two  30°  prisms  and  one  right-angled  prism  from  which  the 
Vol.I.-3  " 


34 


INTRODUCTION. 


light  is  internally  reflected.  Usually  the  prism  is  made  in  one  piece, 
but  with  very  highly  refractive  glass  it  is  built  up  of  the  separate  prisms. 
The  telescope  and  collimator  are  always  at  right  angles,  being  fixed 
in  this  position,  the  different  parts  of  the  spectroscopic  field  being 
brought  across  the  pointer  in  the  eye-piece  of  the  observation  telescope 
(used  instead  of  cross-wires)  by  rotating  the  prism,  this  being  effected 
by  means  of  a  fine  steel  screw,  the  point  of  which  presses  against  a 
projecting  arm  on  the  prism-table.  To  the  screw  is  fixed  a  helical 


PATH  OF  LIGHT. 


FIG.  16. 

drum  (see  Fig.  17)  on  which  the  wave-length  of  the  line  under  observa- 
tion and  coinciding  with  the  cross-wires  in  the  telescope  is  read  off 
directly;  the  wave  length  being  indicated  by  the  index,  which  runs  in  a 
helical  slot. 

With  this  instrument,  which  reads  to  within  2  Angstrom  units  and  in 
which  a  single  high  dispersion  prism  separates  the  two  D  sodium  lines 
by  an  apparent  distance  of  about  1/32  in.,  the  accurate  observation 
of  spectra  is  enormously  simplified.  In  using  the  instrument  the  prism 
is  first  fixed  in  position  by  reference  to  one  or  two  lines  in  the  spectrum. 
For  this  purpose  the  drum  is  first  rotated  until  the  pointer  corresponds 
with  the  wave  length  of  one  of  the  sodium  lines  (D1  or  D2) ;  a  sodium 
flame  is  then  put  before  the  collimator,  the  slit  adjusted  and  the  prism 
rotated  carefully  by  hand,  until  the  sodium  line  chosen  corresponds 
exactly  with  the  bright  pointer  in  the  eye-piece.  To  simplify  the  ad- 
justment, the  bright  pointer  itself  (shown  in  Fig.  18)  can  be  moved 


SPECTROMETERS  AND  SPECTROGRAPHS. 


35 


laterally  by  the  two  milled-head  screws  below;  the  metal  pointer  in  the 
eye-piece  is  ground  exceedingly  fine,  brightly  polished  and  illuminated 
from  above  by  the  small  mirror  (Fig.  18).  When  the  position  of  the 
prism  has  been  found  (an  operation  which  occupies  a  few  minutes  only), 
it  is  clamped  in  position  by  the  top  screw;  its  outline  should,  when  the 
instrument  is  first  used,  be  marked  out  by  pencil  on  the  base  plate. 
On  all  subsequent  occasions  the  prism  is  placed  approximately  in 
position  by  means  of  this  outline  and  can  then  be  accurately  adjusted  in 


FIG.  17 


FIG.  18. 


a  few  moments.  When  the  position  of  the  prism  has  been  fixed  by 
reference  to  the  sodium  line  the  wave-length  scale  gives  the  position  of 
every  other  line  in  the  spectrum.  The  accuracy  of  the  calibration  and 
of  the  adjustment  of  the  prism  can  be  tested  by  reference  to  any  line 
in  the  extreme  blue;  for  instance,  by  means  of  the  blue  caesium  line. 
For  this  purpose  a  trace  of  a  caesium  salt  is  heated  on  a  platinum  wire 
in  a  bunsen  flame. 

To  observe  an  absorption  spectrum,  it  is  only  necessary  to  place  a  lu- 
minous flame — for  example,  a  Welsbach-burner — before  the  collimator 
and  to  interpose  a  trough  (of  a  suitable  thickness)  filled  with  the  liquid 
under  observation.  The  absorption  spectrum  is  then  produced  and 
the  wave  lengths  of  the  absorption  lines  or  bands  can  be  read  off  directly 
on  the  scale  by  turning  the  graduated  drum  until  the  absorption  bands 
correspond  with  the  bright  pointer  in  the  eye-piece.  The  two  shutters 
in  the  eye-piece,  which  can  be  moved  laterally,  are  of  great  service  in 


INTRODUCTION. 


observing  faint  lines,  as  they  can  be  shifted  from  either  side  so  as  to 
cover  any  desired  part  of  the  field  and  thus  prevent  the  eye  from  becom- 
ing fatigued  by  the  glare  in  the  rest  of  the  field. 


FIG.  19. 

A  useful  accessory  to  the  above  spectrometer  is  the  camera  shown  in 
Fig.  19  which  is  used  as  a  spectrograph. 


FIG.  20. 

This  instrument  is  of  service  in  recording  photographs  of  absorption 
spectra. 

When  absorption  occurs  in  the  ultra-violet  region  of  the  spectrum 
it  is  necessary,  in  order  to  obtain  photographs  of  the  absorption  spec- 


SPECTROMETERS  AND  SPECTROGRAPHS. 


37 


trum,  that  the  lenses  and  prism  of  the  spectrograph  be  constructed  of 
special  glass  (ultra-violet  glass)  which  is  transparent  to  the  ultra-violet 
rays;  Fig.  20  shows  a  spectrograph  which  is  suitable  for  use  in  obtain- 
ing photographs,  for  example,  of  the  absorption  bands  of  blood. 


FIG.  21. 

Quartz  lenses  and  prisms  have  to  be  used  when  the  extreme  ultra- 
violet [region — that  is,  the  region  of  smallest  wave  length — has  to  be 
examined.  Fig.  21  shows  a  spectrograph  with  quartz  train  made  by 
Messrs.  Hilger. 


FIG.  22. 


A  much  -cheaper  instrument  than  any  of  the  foregoing  is  Hilger's 
wave-length  spectrometer  (Fig.  22)  of  the  photographic  scale  type; 
measurements  can  be  made  with  it  even  more  rapidly  than  with  the 


30  INTRODUCTION. 

drum-reading  spectrometer,  but   it  is  not  quite  so  accurate.     The 
readings  are,  however,  correct  to  within  about  10  Angstrom  units. 

The  photographic  scale  is  mounted  on  a  tube  (with  collimating  lens), 
and  the  light  from  the  scale  is  reflected  from  the  surface  of  the  prism. 
A  reflected  image  of  the  scale  is  thus  seen  in  the  tele- 
scope in  juxtaposition  to  the  spectrum  as  shown  in  Fig. 
23   which   shows  a  portion  of  the  complex  absorption 
spectrum   of   nitric    oxide.      The    dark  bands  are,  of 
course,    not   sharply   defined  in  this  spectrum.      The 
definition  of  the  scale  is  very  much  finer  than  is  shown 
in  the  print.      The  print  is  the  exact  size  of  the  real 
image  formed  by  the  telescope  object  glass.     To  get  an  idea  of  the 
size  of  field  in  the  instrument,  therefore,  the  print  should  be  looked  at 
with  an  eye-piece. 


FIG.  24. 

The  collimator,  prism  and  photographic  scale  mount  are  fixed  to  a 
rigid  cast-iron  base,  the  telescope  alone  rotating  to  pass  through  the 
spectrum.  To  this  instrument  a  camera  can  also  be  attached  so  as  to 
produce  photographic  records  of  the  spectra  under  examination. 

The  Hiifner  spectrophotometer  (Fig.  24)  made  by  Hilger  is  de- 
signed for  the  accurate  measurement  of  absorption  of  liquids  for  light 
of  any  desired  wave  length.  It  has  found  a  useful  application  in  the 


SPECTROMETERS  AND  SPECTROGRAPHS.          39 

determination  of  the  densities  of  photographic  plates  and,  more  re- 
cently, in  the  quantitative  estimation  of  minute  quantities  of  nitrogen 
peroxide,  such  as  are  produced  by  the  decomposition  of  nitro-explosives 
(see  Robertson  and  Napper,  Trans.  Chem.  Soc.,  1907,  91,  761  and 
764).  It  may  here  be  mentioned  that  the  wave-length  spectrometers 
already  described  are  particularly  convenient  in  carrying  out  the  test 
for  mercury  in  nitro-explosives,  such  as  cordite.  (Compare  the  article 
on  "  Explosives,"  in  Vol.  II.) 

The  Hiifner  spectrophotometer  consists  of  the  following  essentials: 
It  is  desired  to  compare  the  intensities  of  two  beams  of  light,  one  of 
which  has  undergone  absorption  (by  passage,  for  instance,  through  a 
known  thickness  of  a  liquid  under  observation).  In  the  path  of  the 
beam  which  has  not  undergone  absorption  is  interposed  a  Nicol  prism, 
which  polarises  the  light  perpendicularly.  The  two  beams  of  light  are 
then  thrown  on  the  slit  of  the  spectroscopic  portion  of  the  apparatus,  be- 
ing brought  into  close  juxtaposition  with  a  sharp  dividing  line  by  a  prism 
of  special  design.  The  light  after  passing  through  the  slit  undergoes 
collimation,  and  is  spread  into  a  spectrum  by  a  prism,  and  after  passing 
through  a  second  Nicol  prism  is  brought  to  a  focus,  and  observed  by  an 
eye-piece.  Two  spectra  are  then  seen  one  above  the  other  with  a  very 
sharp  dividing  line  between;  the  one  being  an  absorption  spectrum  of 
the  liquid  substance  under  observation,  the  other  spectrum  being  reduci- 
ble by  rotation  of  the  second  Nicol  prism  to  any  desired  intensity.  The 
intensity  of  this  latter  spectrum  can  be  simply  deduced  from  the  rota- 
tion of  the  second  Nicol,  and  thus,  by  exact  matching  of  any  desired 
part  of  the  two  spectra,  an  exceedingly  accurate  measurement  of  the 
amount  of  absorption  of  the  observed  material  can  be  obtained.  One 
can  pass  through  the  spectrum  by  a  screw  motion,  with  a  large 
drum-head  on  which  the  part  of  the  spectrum  under  observation 
is  marked  in  wave  lengths.  Owing  to  the  special  form  of  prism 
used,  the  telescope  is  rigidily  fixed  as  in  the  constant  deviation 
spectrometer. 

The  rotation  of  the  second  Nicol  is  read  off  by  a  vernier.  The 
eye-piece  has  two  shutters  which  can  be  pushed  in  from  right  and  left, 
by  means  of  which  any  part  of  the  spectrum  can  be  isolated.  (See 
page  35,  Fig.  18.) 

The  following  works  deal  with  the  observation  of  absorption 
spectra;  Formanek,  Die  qualitative  Spec tralanalyse  (R.  Muckenberger, 
Berlin);  E.  C.  C.  Ra\y,Spectroscopy  (Longmans).  The  most  exhaus- 


40  INTRODUCTION. 

tive  treatment  of  the  subject  is  contained  in  Kayser's  comprehensive 
"Handbuch  der  Spectroscopie." 

Microspectroscope. —  For  observing  the  absorption-spectra  of 
organic  substances  a  pocket  spectroscope  will  often  suffice,  but  it 
is  far  better  to  employ  a  microspectroscope,  furnished  with  a  proper 
comparison  stage  and  reflecting  prism,  so  as  to  allow  of  the  spectrum 
of  the  colouring  matter  under  examination  being  viewed  in  juxtaposi- 
tion with  the  spectra  of  standard  specimens  of  known  origin. 

Fluorescence  of  organic  bodies  is  a  qualitative  character  often 
of  much  value.  It  is  absolutely  necessary  that  the  liquid  to  be 
observed  should  be  perfectly  clear,  as  the  presence  of  minute  suspended 
particles  may  lead  to  fallacious  conclusions. 

As  a  rule,  the  phenomenon  of  fluorescence  may  be  observed  by 
filling  a  small  test-tube  with  the  fluorescent  liquid,  holding  it  in  a 
vertical  position  before  a  window,  and  observing  the  liquid  from  above 
against  a  dark  background.  Another  plan  is  to  make  a  thick  streak  of 
the  liquid  on  a  piece  of  polished  jet  or  black  marble,  or  on  a  glass  plate 
smoked  at  the  back,  and  to  place  the  streaked  surface  in  front  of,  and 
at  right  angles  to,  a  well-lighted  window.  Either  of  these  methods  is 
superior  to  the  polished  tin  plate  sometimes  recommended.  The 
background  should  be  black,  not  white. 

In  some  cases,  the  following  method  of  observing  fluorescence  may 
be  advantageously  employed.  A  cell  is  made  by  cementing  a  piece  of 
barometer-tube  about  3/4  in.  in  length,  and  having  an  internal  diam- 
eter of  1/6  in.,  to  a  glass  microscope-slide,  by  means  of  black  sealing- 
wax.  The  open  end  of  the  cell  must  be  well  polished.  On  introduc- 
ing a  clear  solution  of  any  fluorescent  substance,  covering  the  cell  with 
a  piece  of  thin  glass,  placing  the  slide  on  the  stage  of  a  microscope, 
illuminating  the  tube  at  the  side  by  means  of  strong  daylight,  and 
looking  down  and  observing  the  axis  of  the  cell  by  a  low  microscopic 
power,  the  liquid  will  appear  more  or  less  turbid  and  of  a  colour 
dependent  on  the  nature  of  the  fluorescent  substance  in  solution.  If 
no  fluorescent  substance  be  present,  the  field  will  appear  perfectly 
black,  as  no  light  is  reflected  either  from  the  apparatus  or  the  liquid. 
For  a  sensitive  method  of  detecting  fluorescence  see  Francesconi 
and  Bargellini,  Atti  dei  Lincei  1906,  [5]  15,  No.  3.  When  desired, 
the  spectrum  of  the  fluorescent  light  can  be  observed  by  the  micro- 
spectroscope.  In  some  instances  the  spectrum  thus  obtained  shows 
remarkable  and  characteristic  bands. 


POLARIMETERS.  4! 

Double  refraction,  as  observed  under  the  microscope  by  means  of 
polarised  light,  is  often  of  value  for  the  recognition  of  organic  bodies. 
In  addition  to  the  well-known  phenomena  dependent  on  crystalline 
form,  many  organic  substances  not  actually  crystalline  exhibit  a  cross 
and  series  of  rings  when  viewed  by  polarised  light.  This  is  notably 
the  case  with  many  of  the  starches,  and  furnishes  a  valuable  means  for 
their  discrimination.  The  optical  properties  of  crystals  often  serve 
as  a  means  of  identification.  For  the  use  of  the  polarising  miscroscope 
in  this  connection  see  Weinschenk,  Anleitung  zum  Gebrauch  des 
Polarisatiom-Mikroskops,  Freiburg,  1906. 

POLARIMETERS. 

Rotation  of  the  Polarised  Ray. — Organic  substances  containing 
a  so-called  asymmetric  carbon  atom  possess  the  power  of  rotating  the 
plane  of  polarisation  of  a  luminous  ray;  as  this  property  is  exerted 
even  by  the  solutions  of  optically  active  substances,  the  angle  through 
which  the  rotation  occurs  often  serves  for  the  accurate  estimation 
of  certain  compounds  The  method  is  much  employed  in  the  examina- 
tion of  saccharine  substances. 

Construction  of  Polarimeters. — In  all  forms  of  apparatus  for 
measuring  the  rotation  of  the  plane  of  polarisation  of  a  luminous  ray, 
the  polariser,  or  optical  means  of  obtaining  a  beam  of  polarised  light, 
consists  of  a  double-refracting  prism  of  calcite.  In  some  cases  a  double- 
image  prism  is  used,  but  in  others  the  extraordinary  ray  only  is  employed. 
The  analyser  is  composed  of  a  Nicol  prism,  with  a  suitable  eye-piece. 
On  rotating  the  analyser  through  90°  the  field  becomes  perfectly  dark, 
but  on  introducing  between  the  analyser  and  polariser  a  tube  filled  with 
sugar  solution  or  other  optically  active  liquid  the  light  again  passes. 
With  white  light  the  transmitted  tint  differs  with  the  strength  of  the 
solution  of  sugar  and  the  length  of  the  tube,  and  rotation  of  the 
analyser  merely  causes  an  alteration  in  the  colour  of  the  trans- 
mitted light,  a  phenomenon  due  to  the  fact  that  rays  of  differing 
refrangibility  are  rotated  unequally  (rotatory  dispersion).  If  mono- 
chromatic light  be  employed,  a  certain  angular  rotation  of  the 
analyser  will  suffice  wholly  to  extinguish  the  light  from  the  field  of 
view,  and  hence,  by  measuring  the  angle  through  which  the  analyser 
must  be  rotated  to  restore  darkness,  an  estimate  of  the  strength 
of  the  interposed  liquid  in  sugar  or  other  active  constituent  may 


42  INTRODUCTION. 

be  obtained.  Quartz  possesses  powerful  rotatory  action,  a  plate 
3.75  mm.  in  thickness  (-=0.148  in.)  rotating  the  plane  of  polar 
isation  of  the  mean  yellow  ray  through  90  degrees.  Some  specimens 
of  quartz  are  dextrorotatory,  others  are  laevorotatory.  Hence,  a  double 
plate  composed  of  equal  thicknesses  of  the  two  varieties  possesses  no 
rotatory  power.  If  a  plate  composed  of  semicircles  of  right-  and  left- 
handed  quartz,  each  3.75  mm.  in  thickness,  is  placed  between  Nicol's 
prisms,  while  the  principal  sections  of  the  latter  are  parallel,  the  field 
assumes  a  peculiar  purple,  known  as  the  transition  tint.  The  least 
rotation  of  the  analyser  causes  one  half  of  the  circle  to  incline  to  red 
and  the  other  half  to  violet,  and  the  interposition  of  a  solution  of  an 
optically  active  substance  produces  a  similar  effect,  while  to  restore  uni- 
formity of  tint  necessitates  a  rotation  of  the  analyser  through  an  angle 
dependent  on  the  strength  and  thickness  of  the  polarising  liquid  used. 

Laurent's  polarimeter  is  one  of  the  simplest.  One-half  of  the  field  of 
vision  is  covered  by  a  very  thin  plate  of  quartz  which  causes  an  altera- 
tion in  phase  of  half  a  wave  length  and  allows  light  to  pass,  even 
when  the  analyser  and  polariser  (both  of  which  are  Nicol's  prisms) 
are  crossed.  If  the  analyser  be  rotated  so  as  to  cause  the  quartz  plate 
to  become  dark,  light  passes  through  the  uncovered  half  of  the  field. 
In  a  position  intermediate  between  these  two  the  two  halves  of  the 
field  appear  equally  dark,  and  this  is  the  zero  point  of  the  instrument. 
The  slightest  deviation  from  this  neutral  position  causes  one  half  of  the 
field  to  appear  darker  and  the  other  half  lighter  than  before.  Hence 
the  change  is  a  double  one  and  the  instrument  is  thus  made  very  sen- 
sitive. Monochromatic  light  must  be  used. 

The  Lippich  polarimeter,  now  widely  used,  is  also  a  half-shadow 
instrument  differing  from  the  Laurent  polarimeter  in  the  method 
adopted  for  producing  the  half  shadow,  a  small  Nicol  prism  replacing 
the  quartz  plate.  Triple-field  instruments  have  also  been  devised. 
In  these  the  field  is  divided  vertically  into  three  zones,  the  central 
one  being  a  broad  band.  The  optical  construction  is  such  that  the 
lateral  zones  always  agree  in  tint,  thus  making  the  contrast  with  the 
central  portion  more  marked.  In  one  form  of  instrument  the  por- 
tions of  the  field  are  concentric.  It  is  claimed  that  this  method  gives 
a  high  degree  of  delicacy  (see  below). 

The  use  of  monochromatic  light,  desirable  in  saccharimetry,  is  essen- 
tial in  estimating  many  substances.  This  is  due  to  the  fact  that 
Biot's  law,  that  the  angles  of  rotation  for  the  different  simple  colours 


POLARIMETERS.  43 

are  proportional  to  the  squares  of  the  indices  of  refraction  and  in- 
versely as  the  squares  of  the  wave-lengths,  is  true  of  quartz  and  sac- 
charine liquids,  but  does  not  hold  good  generally.  In  all  cases,  to 
insure  accuracy,  not  only  should  monochromatic  light  be  employed 
but  the  liquid  under  observation  be  kept  at  a  known  temperature. 

For  monochromatic  light,  the  lamp  usually  employed  is  a  bunsen 
burner  with  a  ledge  at  the  top  for  holding  some  solid  sodium  compound 
A  fused  mixture  of  sodium  chloride  and  phosphate  is  better  than 
sodium  chloride  alone.  The  following  is  an  excellent  method  for  ob- 
taining a  steady,  strong  yellow  light:  Strips  of  common  filter-paper 
5  cm.  wide  and  about  50  cm.  long  are  soaked  in  a  strong  solution  of 
sodium  chloride  and  thiosulphate,  dried,  and  rolled  into  a  hollow 
cylinder  of  such  size  as  to  fit  firmly  on. the  top  of  the  burner.  The 
cylinder  is  kept  from  unrolling  by  a  few  turns  of  fine  iron  wire.  The 
flame  burns  at  the  top  of  the  cylinder,  giving  for  the  first  few  minutes 
a  luminous  cone,  but  soon  becoming  pure  yellow.  The  cylinder  be- 
comes a  friable  charred  mass,  but  if  not  disturbed  may  be  used  for 
some  time  continuously  or  at  intervals. 

An  effective  method  for  producing  a  sodium  flame  is  that  devised  by 
Caldwell  and  Whymper  (Proc.  Roy.  Soc.,  1908,  A  81,  112-117).  A 
Meeker  burner  is  taken  off  the  ordinary  base,  screwed  to  a  piece  of 
brass  tubing  and  fixed  in  an  ordinary  glass  bottle  by  means  of  a 
rubber  stopper.  The  gas  supply  is  led  into  the  bottle  by  a  glass  tube 
and  passes  through  a  powder  consisting  of  an  intimate  mixture  of 
finely  ground  dry  sodium  carbonate  and  clean  sand.  The  sand  is 
necessary  to  prevent  the  particles  of  sodium  carbonate  from  caking. 
So  much  sodium  carbonate  is  blown  up  that  the  whole  flame  (6  by 
ij  inches)  is  uniformly  coloured  an  intense  yellow.  It  has  about  60 
candle  power. 

H.  W.  Wiley  has  pointed  out  the  usefulness  of  acetylene  as  a  source 
of  light  for  polarimetric  work.  By  the  use  of  this  light  he  was  able  to 
make  readings  through  liquids  which  were  too  dark  to  permit  light 
from  ordinary  sources  to  pass.  Since  acetylene  can  be  readily  and 
safely  prepared  by  self-regulating  apparatus,  it  will  doubtless  find 
application  in  this  and  in  other  departments  of  laboratory  work. 
Landolt  recommends  an  Aron's  mercury  vapour  lamp  as  a  convenient 
means  of  obtaining  monochromatic  light  in  polarimetry.  Lowry  has 
employed  (Proc.  Roy.  Soc.,  Nov.  19,  1908),  the  Bastian  mercury 
lamp  with  great  advantage  in  measuring  rotatory  dispersion. 


44  INTRODUCTION. 

Before  using  the  polarimeter  the  observing  tube  should  be  filled 
with  distilled  water  and  placed  in  position  between  the  polarising  and 
analysing  prisms,  which  are  then  to  be  adjusted,  so  that  the  latter 
shall  be  at  the  zero  point  of  the  scale  when  there  is  no  optical  dis- 
turbance of  the  field.  The  tube  is  then  filled  with  the  solution  to  be 
tested  and  replaced  between  the  polariser  and  analyser,  when,  if  it 
contain  an  active  substance,  an  optical  disturbance  will  be  observed, 
the  extent  and  direction  of  which  will  depend  on  the  amount  and 
nature  of  the  rotating  substance  under  examination.  The  polari- 
meter is  then  adjusted,  so  that  the  neutral  point  is  reached,  or,  in 
other  words,  so  that  the  optical  disturbance  produced  by  the  intro- 
duction of  the  rotating  liquid  is  compensated;  the  rotation  required 
to  produce  this  effect  is  then  read  and  recorded.  From  the  circular 
rotation  observed,  the  specific  rotatory  power  of  the  substance  may 
be  calculated  in  the  manner  described  in  the  next  paragraph. 

Full  directions  for  the  preparation  of  the  solution  and  the  practical 
management  of  the  polarimeter  will  be  found  in  the  section  on  the 
"Sugars.'' 

Specific  Rotatory  Power.  —  The  specific  rotatory  power  of  an  op- 
tically active  substance  is  the  angular  rotation  exerted  by  it  on  a  ray  of 
polarised  light  traversing  a  thickness  of  i  decimetre  (  =  3.937  ins.)  of 
the  substance. 

The  absolute  specific  rotatory  power  of  a  solid  can  only  be  observed 
by  using  thick  slices  of  considerable  transparency.  It  is  usual  to 
operate  on  a  solution  of  known  concentration,  and  from  the  sensible  or 
apparent  specific  rotatory  power  observed,  to  calculate  the  absolute 
rotatory  power  of  the  solid  substance. 

The  apparent  specific  rotatory  power  of  a  substance  in  solution  [a] 
is  obtained  from  the  following  measurements: 

a  =  The  observed  angle  of  rotation  in  degrees. 

c  =  The  concentration  of  the  solution  is  grm.  per  100  c.c. 

L  =  The  length  of  the  column  of  solution  in  mm. 


The  apparent  specific  rotatory  power  of  a  substance  varies  greatly 
with  the  wave  length  of  the  light  employed  (rotatory  dispersion)  ;  it  is 
therefore  necessary  to  make  the  measurements  with  monochromatic 
light  of  one  particular  wave  length  and  to  state  the  position  in  the 


POLARIMETERS.  45 

spectrum  of  the  particular  ray  employed.  In  practice  the  rotation  of 
a  substance  is  expressed  in  two  ways.  Either  it  is  referred  to  the  D  line 
of  the  solar  spectrum,  the  rotation  being  then  expressed  by  [a]D;  or  it 
is  referred  to  the  "medium  yellow  ray"  (janne  moyeri)  which  is  com- 
plementary to  Biot's  transition  tint;  the  rotation  being  then  denoted 
by  My.  In  the  former  case  [a]D  is  measured  by  a  Wild,  Mitscherlich, 
Jellet-Cornu  or  Laurent  instrument  and  the  direct  rotation  is  found 
in  degrees  of  arc.  In  the  latter  case,  My  is  measured  by  means  of  a 
neutral-tint  or  half-shadow  polarimeter,  such  as  the  Ventzke-Scheibler. 
The  scale  divisions  in  such  instruments  are  arbitrary  and  have  to  be  con- 
verted into  angular  degrees  before  the  specific  rotatory  power  can  be 
calculated.  The  readings  obtained  being  based  on  the  rotation  of  a 
quartz  plate  are  obtained  in  terms  of  the  rotation  of  a  quartz  plate  of 
definite  thickness.  Whilst  the  rotatory  dispersion  of  quartz  and  cane- 
sugar  solutions  are  nearly  identical,  most  other  substances  have  a  very 
different  rotatory  dispersion  from  that  of  quartz.  Thus,  a  quartz  com- 
pensating instrument  can  only  be  used  in  the  comparison  of  rotatory 
powers  of  different  substances,  when  the  rotatory  dispersion  of  the 
substance  under  examination  is  known  relatively  to  that  of  quartz. 

The  wave  length  of  the  "mean  yellow"  ray  being  less  than  that  of 
the  D  line,  the  numerical  value  of  My  is  greater  than  that  of  [a]D. 
With  a  quartz  plate  i  mm.  thick,  Broch  found 


My=24-5 

Whence:  [a],-  =  1.1306  [a]D  or  approximately  9/8  [a]D. 
[a]D  =  0.8845  My  or  approximately  8/g'[a]r 

The  proportion  between  My  and  MD  varies  in  different  substances 
owing  to  their  having  a  different  rotatory  dispersion. 

For  sugar  solutions  My  :  MD  =  I-I29- 

(Very  nearly  the  same  as  for  quartz.) 

For  camphor  solutions  in  alcohol  the  ratio  is  1.198  and  for  oil  of  tur- 
pentine 1.243. 

Use  of  the  Polarimeter.  —  Fig.  25  shows  a  Schmidt  &  Haensch 
polarimeter  of  the  Lippich  half-shadow  type  with  divided  circle 
reading  by  magnification  to  0.01°.  It  is  intended  for  use  with  a 
sodium  flame,  a  gas  burner  for  this  purpose  being  supplied  with  the 
instrument.  This  instrument  is  chosen  as  being  a  typical  half-shadow 


46 


INTRODUCTION. 


instrument  and  is  now  in  general  use.  For  a  complete  account  of  the 
construction  of  the  many  types  of  polarimeters,  the  influence  exercised 
by  solvents  and  temperature  in  the  specific  rotatory  power,  Landolt's 
treatise,  "Das  optische  Drehungsvermogen"  (F.  Vieweg  und  Sohn, 
Braunschweig,  should  be  consulted.  An  English  translation  has  been 
made  by  J.  H.  Long.1 


FIG.  25. 


In  the  above  illustration  F  indicates  the  telescope,  /  /  the  magnifying 
glasses,  n  n  the  two  verniers,  K  the  graduated  dial,  A  the  analysing 
Nicol  prism,  which  is  fixed  to  the  revolving  graduated  dial  and  to  the 
telescope,  and  P  the  movable  polariser,  with  the  graduated  segment  h  of 
a  circle  fixed  to  it,  and  S  a  small  tube  for  dichromate  solution. 
The  sodium  lamp  is  placed  at  a  distance  of  36  cm.  from  the  appa- 
ratus. It  consists  of  a  Bunsen  burner  (or  a  Barthel's  spirit  burner) 
supplied  with  a  platinum  ring  on  which  some  pulverised  sodium  chlo- 
ride is  placed  and  made  intensely  incandescent  by  means  of  the  non- 

1For  a  useful,  concise  description  of  many  types  of  polarimeter  and  details  of  manipula- 
tion, Messrs.  Baird  &  Tatlock's  catalogue  may  be  consulted  with  advantage. 


POLARIMETERS. 


47 


luminous  ilame  from  the  burner;  the  apparatus  is  pointed  towards 
the  brightest  part  of  the  yellow  flame,  which  can  easily  be  accomplished 
by  means  of  the  adjuster  provided  with  the  lamp. 

The  graduated  dial,  which  is  made  to  revolve  by  means  of  a  knob  T, 
is  as  a  rule  graduated  all  the  way  round.  In  addition  to  whole  degrees, 
half  and  quarter  degrees  are  indicated  on  the  dial;  24  such  quarter 
degrees  are  divided  on  the  2  verniers  into  25  divisions,  therefore  a 
scale  mark  on  the  vernier  coinciding  with 
any  one  scale  mark  on  the  dial  indicates  0.01°. 
Fig.  26  shows  the  inner  revolving  dial  and  the 
exterior  vernier;  the  zero  line  of  the  vernier  is 
shown  between  the  13.50  and  the  13.75°  ^ne 
of  the  dial;  the  0.16  of  the  vernier,  coincides 
with  a  line  on  the  dial,  therefore  the  total 
reading  is  13.50  +  0.16  =  13.66°. 

If  desired,  a  second  scale  can  be  provided 
on  the  dial  to  show  directly  percentage  of  some 
other  sugar.  This  is  done  by  dividing  the 
dial  into  whole  percentages;  nine  such  are 
divided  on  the  vernier  into  10  divisions,  so  that 
the  vernier  reads  to  o.i  per  cent.  The  reading 
is  made  in  the  same  manner  as  described 
above;  the  beet-sugar  scale  is  based  on  the  FIG.  26. 

standard  weight  of  26.048  grm.     The  100  line 

100%)  corresponds  with  a  solution  of  26.048  grm.  of  chemically  pure 
sugar  in  a  100  c.c.  flask,  examined  with  the  200  mm.  tube.  The 
so-called  grape-sugar  scale  is  now  rarely  used,  but  if  a  tube  of  a 
certain  length  (according  to  the  most  recent  researches  189.4  mm.)  is 
used  in  connection  with  the  degree  scale,  the  percentages  can  also  be 
found  directly,  one  degree  in  this  case  corresponding  exactly  to  i%  of 
so-called  " grape  sugar." 

The  adjustment. — When  the  above  apparatus  is  well  illuminated  by 
the  sodium  flame,  the  zero  position  (the  starting-point  of  all  experi- 
ments) must  first  be  found;  this  is  indicated  by  the  two  halves  of  the 
field  appearing  equally  illuminated  (equal  half-shadows).  For  this 
purpose  the  telescope  F  is  focussed  on  the  Lippich's  polariser,  so  that 
the  field  presents  a  perfectly  clear,  round  circle  divided  into  two  equal 
parts  by  a  sharply  defined  vertical  line.  If  the  graduated  dial  is  turned 
through  3  or  4  degrees  to  either  the  right  or  the  left  of  the  zero  line, 


48  INTRODUCTION. 

it  will  be  seen  that  one-half  of  the  field  will  become  lighter,  the  other 
half  darker. 

The  zero  position  is  first  adjusted  so  that  the  zero  line  of  the  circle 
coincides  with  the  zero  line  of  the  vernier.  The  half-shadow  can  now 
be  made  lighter  or  darker,  according  as  the  polariser  is  turned  to  right  or 
left  of  the  zero  line  by  means  of  the  pointer  h.  When  the  pointer  //  is  at 
zero  and  the  analyser  A  also  at  zero,  both  halves  of  the  field  appear 
black.  The  nearer  the  pointer  is  to  the  zero  line  the  darker  the  half- 
shadow  and  the  more  sensitive  the  apparatus.  In  cases  when  the  solu- 
tion is  not  quite  transparent,  the  pointer  must  be  moved  slightly  away 
from  the  zero  line  so  that  the  field  is  clear.  The  instrument  is  usually 
so  adjusted  that  the  position  of  the  pointer  is  at  7  J°  when  the  disc  and 
vernier  read  exactly  o°.  When  the  pointer  is  moved  the  zero  of  the 
apparatus  changes  and  no  longer  corresponds  with  the  zero  of  the  dial. 
The  simplest  method  is  then  to  take  into  account  the  difference  in  the 
position  of  the  zero  line  of  the  dial  and  the  zero  line  of  the  apparatus;  or 
the  graduated  dial  is  moved  to  o°  and  the  apparatus  placed  in  the  zero 
position  by  turning  the  analysing  Nicol  by  the  screw  A  to  the  right  or 
left  until  the  half-shadows  are  equal  in  tint. 

The  following  points  must  be  especially  observed  during  a  measure- 
ment: 

1.  When  the  circle  has  been  turned  too  far  and  the  sensitive  range  of 
the  apparatus  has  been  lost  it  is  easy  to  mistake  the  zero  position  owing 
to  the  light  appearing  nearly  of  the  same  intensity  on  both  sides  of  the 
vertical  line.     Even  if  the  circle  is  then  turned  through   10  or  15° 
hardly  any  change  will  be  observed.     It  is,  therefore  important,  especi- 
ally when  the  sample  under  examination  has   been   placed  within 
the  apparatus,  to  make  sure  that  the  transition  from  light  to  shade, 
and  vice  versa,  is  instantaneous  when  the  circle  is  turned  a  few  degrees 
on  either  side  of  the  zero. 

2.  When  the  sample  to   be  tested  is  inserted,  the  telescope  must 
first  of  all  be  adjusted  accurately  so  that  the  field  is  quire  clear  and 
equally  divided  by  the  vertical  line;  the  circle  is  then  turned  until  the 
shades  are  exactly  of  the  same  intensity  in  the  two  portions  of  the  field. 

Precautions  to  be  Observed. — Before  the  polarimeter  tube  is  filled  it 
should  be  thoroughly  dried  by  pushing  a  plug  of  filter-paper  or  cotton 
wool  through  it,  or  it  should  be  rinsed  several  times  with  the  solution 
to  be  used.  The  cover-glasses  must  be  free  from  scratches  and  thor- 
oughly clean  and  dry.  Unnecessary  warming  by  the  heat  of  the  hand 


POLARIMETERS. 


49 


during  filling  should  be  avoided;  the  tube  is  closed  at  one  end  by  the 
screw-cap  and  cover-glass  and  grasped  at  the  other  with  the  thumb 
and  finger.  The  tube  is  filled  with  the  solution  until  the  meniscus 
projects  slightly  above  the  opening,  the  air  bubbles  are  allowed  time 
to  rise  and  the  cover-glass  then  pushed  horizontally  over  the  end  of  the 
tube  in  such  a  way  that  the  excess  of  liquid  is  carried  over  the  side, 
leaving  the  cover-glass  exactly  closing  the  tube  without  air  bubbles 
beneath  it  and  without  any  liquid  on  its  upper  surface.  After  the 
cover-glass  is  in  position  the  tube  is  closed  by  screwing  on  the  cap,  care 
being  taken  that  too  great  a  pressure  is  not  exerted,  for  this  might  pro- 
duce a  rotatory  power  in  the  glass  itself  and 
thus  give  rise  to  erroneous  readings.  The 
rubber  washers  must  therefore  be  placed  in  a 
proper  position  and  the  caps  screwed  in  lightly. 
Before  taking  the  actual  reading,  observa- 
tions are  made  of  the  zero  and  with  a  standard 
quartz  plate  of  known  rotation.  The  mean  of 
several  readings  is  taken  and  corrected  for  any 
deviation  of  the  zero. 

In  the  polarisation  of  the  quartz  plates  and 
colourless  solutions,  difficulty  may  be  experi- 
enced in  obtaining  a  complete  correspondence 


FIG.  27. 


FIG.  28. 


of  both  halves  of  the  field.  This  may  be  overcome  and  the  neutral 
point  found,  but  when  it  cannot,  the  ordinary  eye-piece  of  the  instru- 
ment may  be  replaced  by  another  which  is  supplied  with  the  polari- 
scope,  and  which  carries  a  section  of  a  crystal  of  potassium  dichromate. 
This  removes  the  difficulty  and  renders  it  possible  to  obtain  a  field  of 
exact  neutrality. 

In  the  latest  types  of  polarimeter  the  optical  field  is  divided  into  three 
parts  instead  of  two  as  in  the  half-shadow  instruments.     Such  instru- 
ments are  more  accurate,  the  equality  of  the  field  being  capable  of  a 
more  delicate  adjustment. 
Vol.  I.— 4 


50  INTRODUCTION. 

The  arrangement  is  that  shown  in  Fig.  27.  In  the  zero  position 
i,  2  and  3  are  equally  illuminated  while  in  any  other  position  i  is  dark, 
while  2  and  3  are  illuminated  or  i  is  bright  and  2  and  3  equally  dark. 

Ring-shadow  polarimeters  (Fig.  28)  are  a  modification  of  the  half- 
shadow  instruments. 

They  are  used  in  precisely  the  same  way  as  the  ordinary  half-shadow 
polarimeters,  but  the  field  of  view  is  divided  into  two  concentric  portions 
instead  of  into  two  semicircular  segments.  With  this  arrangement  the 
instrument  is  capable  of  finer  adjustment  and  the  eye  is  much  less 
fatigued  than  when  using  the  half-shadow  polariser. 

Fig.  29  shows  an  improved  form  (German  patent)  of  tube  used 
for  holding  the  solution  to  be  examined  in  the  polarimeter.  Air  bubbles 


FIG.  29. 

enclosed  in  the  tube  disappear  into  the  enlargement  a  at  one  end  of  the 
tube  and  so  cease  to  give  trouble  during  the  observation.  The  caps 
are  of  brass  and  are  screwed  on  as  shown.  This  pattern  of  tube  is 
particularly  useful  in  dealing  with  volatile  liquids,  such  as  chloroform. 

A  specially  cheap  form  of  half-shadow  polarimeter  of  the  Mitscher- 
lich  type  in  shown  in  Fig.  30,  which  reads  to  o.i°and  has  been  de- 
signed for  the  estimation  of  sugar  and  albumin  in  urine. 

Behind  the  analyser  is  a  small  telescope,  and  behind  the  polariser  a 
semicircular  plate  of  quartz.  The  telescope  is  focussed  on  to  this  plate, 
and  the  field  of  vision  appears  as  a  circle  divided  into  two  halves. 
A  pointer  is  attached  to  the  analyser,  which  moves  to  the  right  or  left 
on  a  metal  disc  divided  into  angular  degrees.  A  vernier  upon  which 
10  divisions  correspond  to  9  divisions  of  the  disc  enables  the  observer 
to  read  tenths  of  an  angular  degree  and  estimate  twentieths. 

The  instrument  is  constructed  for  monochromatic  light.  A  sodium 
lamp  must  therefore  be  used  as  the  source  of  illumination.  The  zero 
point,  as  in  other  half-shadow  instruments,  is  found  when  both  halves 
of  the  field  are  of  the  same  tint. 

The  tube  filled  with  the  liquid  to  be  examined  is  placed  in  the  in- 
strument, and  after  having  focussed  the  plate  by  means  of  the  telescope, 
the  pointer  is  turned  to  the  right  or  left  according  to  whether  the  solu- 


POLARIMETERS.  51 

tion  is  dextro-  or  laevorotatory,  until  both  halves  of  the  disc  are  again 
equally  tinted. 

If  the  instrument  is  to  be  used  for  general  work,  a  tube  of  the  length 
of  200  mm.  is  supplied,  and  another  of  100  mm.  for  dark  coloured 
solutions,  but  when  used  exclusively  for  urine  it  is  more  convenient 
to  have  one  of  189.4  mm.  and  another  of  half  that  length.  These 
tubes  give  at  once  the  percentage  by  volume  of  sugar  and  albumin, 


FIG.  30. 

each  degree  being  equal  to  i  grm.  in  TOO  cc.     Albumin  polarises  to  the 
left  to  the  same  extent  as- glucose  does  to  the  right. 

The  estimation  of  sugar  and  albumin  in  urine  is  effected  in  the  fol- 
lowing manner:  The  urine,  if  necessary,  is  filtered.  Should  it  be  too 
dark  coloured  to  be  read  in  the  long  tube,  the  short  one  is  tried,  and  if 
still  too  dark,  some  extracted  animal  charcoal  is  added,  and  the  whole 
well  shaken.  In  the  event  of  this  not  effecting  decolourisation,  100  c.c. 
of  the  urine  is  introduced  into  a  flask  graduated  to  contain  100  and  no 
c.c.,  basic  acetate  of  lead  is  added  to  the  no  c.c.  mark,  the  mixture  is 
then  shaken  and  filtered,  and  the  reading  multiplied  by  o.n  to  correct 
for  dilution.  The  temperature  should  be  15°  to  20°  C.  If  the  urine 
is  free  from  albumin  the  reading  corresponds  to  the  percentage  of 


52  INTRODUCTION. 

sugar.  Should  it  contain  albumin,  a  few  drops  of  acetic  acid  are  added 
to  100  c.c.  and  the  solution  boiled,  cooled,  filtered,  and  made  up  again 
to  volume  at  15°  to  20°  C. 

As  it  is  necessary  to  maintain  a  known  constant  temperature  in  order 
that  accurate  and  comparable  measurements  can  be  made  with  the 
different  types  of  polarimeters,  water  or  steam  jacketed  tubes  are  sup- 
plied by  the  different  makers  in  which  the  solution  to  be  examined  can  be 


FIG.  31. 

heated  at  an  approximately  constant  temperature.  Full  information 
as  to  these  are  generally  given  in  the  catalogues  of  dealers  in  scientific 
apparatus.  The  special  form  of  thermostat  due  to  Lowry,  which  is 
described  in  detail  elsewhere  (page  55),  enables  a  flow  of  water  to  be 
constantly  circulated  through  a  polarimeter  tube  at  a  temperature 
which  can  be  maintained  constant  to  within  a  few  thousandths  of  a 
degree. 

Fig.  31  shows  a  polarimeter  made  by  Hilger,  of  London,  taking 
tubes  200  mm.  in  length.  The  field  of  view  is  of  the  following  form 
(Fig.  32),  in  which  the  illumination  of  the  middle  strip  decreases  in  in- 


THERMOSTATS.  53 

tensity  when  the  outer  increases,  and  vice  versa.  The  brightness  of 
the  illumination  can  be  varied  by  rotation  of  the  polariser;  an  index 
and  clamp  are  provided  for  the  setting  of  this  adjustment. 

The  table  showing  the  apparent  specific  rotatory  powers  of  different 
organic  substances  which  was  included  in  previous  editions  of  this 
work  has  been  omitted  in  the  present  edition,  because  the  value  ofthe 
specific    rotatory    power    of    a    substance 
differs  widely  with   the   solvent  used  and 
with  the  temperature  and  concentration  of 
the  solution;  numbers  expressing  the  rota- 
tory power  are,  therefore,  misleading  unless 
the  exact  conditions  observed  in  measure- 
ment are  specified.     For  details  concerning 
all  questions  of  polarimetry  and  a  discus- 
sion of  the  influence  exerted    by  solvents, 
etc.,  Landolt's  "  Optische  Drehungsvermogen 
should  be  consulted.     All  available  numer- 
ical data  for  the  rotatory  power  of  organic  substances  are  included  in 
that  work. 

Comparison  of  Scales  of  Various  Instruments. — Polarimeters 
are  now  usually  provided  with  a  scale  reading  to  100  when  a  certain 
quantity  of  sucrose,  called  the  normal  weight,  is  dissolved  in  water  and 
made  up  to  100  c.c.  This  scale  is  known  as  "Ventzke,"  "  Schmidt 
and  Haensch,"  and  "sugar"  scale. 

The  following  factors  may  be  employed  for  the  conversion  of  data 
obtained  by  different  instruments: 

i  division  Schmidt  and  Heensch  (Ventzke)  0.3468°  angular  rotation  D. 

i°  angular  rotation  D  2.8835  divisions  Schmidt  and  Haensch. 

i°  angular  rotation  D  O'TSS1  division  Wild. 

i  division  Laurent  0.2167°  angular  rotation  D. 

i°  angular  rotation  D  4-6154  divisions  Laurent. 

ARRANGEMENTS    FOR    MAINTAINING  A  KNOWN 
CONSTANT  TEMPERATURE. 

Several  types  of  thermostat  have  been  devised  for  the  purpose  of 
making  physico-chemical  measurements  in  a  bath  at  a  known  tem- 
perature; these  are  described  in  treatises  on  physical  chemistry  (e.  g., 
Ostwald-Luther,  Physiko-chemische  Messungen;  Findlay,  Practical 
Physical  Chemistry}.  Lowry  (Trans,,  1905,  87,  1030  to  1034)  gives  an 


54 


INTRODUCTION. 


THERMOSTATS. 


55 


account  of  a  series  of  tests  of  gas  regulators  of  different  patterns  used 
to  control  the  temperature  of  a  bath  containing  30  litres  of  water  and 
well  stirred  by  a  paddle  driven  by  a  water  motor.  Two  forms  of  regu- 
lator are  described,  by  means  of  which  a  known  temperature,  e.  g.,  20°, 
can  be  maintained  in  the  bath  within  a  few  thousandths  of  a  degree 
over  a  long  period.  In  a  later  paper  (Lowry,  Trans.  Faraday  Society, 
1907,  3)  a  thermostat  is  described,  by  means  of  which  a  flow 
of  water  can  be  obtained,  suitable  for 
heating  a  polarimeter  tube  or  refractom- 
eter  prism  at  a  constant  known  temper- 
ature; even  when  the  rate  of  flow  of  the 
water  circulation  is  4  litres  a  minute,  the 
temperature  in  the  bath  does  not  vary  by 
more  than  a  few  thousandths  of  a  degree. 
This  form  of  thermostat  is  particularly 
serviceable  in  the  examination  of  Explo- 
sives. (See  Vol.  II.) 

This  apparatus  (made  by  Messrs. 
Baird  &  Tatlock),  which  the  writer  has 
seen  in  constant  use  during  long  periods 
and  which  needs  practically  no  attention, 
is  constructed  as  follows* 

The  container,  as  shown  in  Fig.  33, 
consists  of  a  large  zinc-lined  box,  20  X  18 
X  1 6  ins.,  with  a  capacity  of  over  70 
litres.  The  liquid  is  stirred  by  a  pro- 
peller driven  by  an  electric  motor.  The 
bulk  of  well-stirred  water  and  the  heat 
insulation  of  the  wooden  box  and  cover  render  the  regulation  of  the 
bath  temperature  exceptionally  easy,  with  the  result  that  when  the  gas 
flame  is  controlled  by  a  4-in.  spiral  (shown  at  3  in  the  figure,  and  in 
detail  in  Fig.  34),  the  variations  are  so  small  that  they  escape  detec- 
tion even  with  a  thermometer  graduated  in  hundredths  of  a  degree. 
The  heating  is  effected  by  means  of  a  small  bat  's-wing  burner  placed 
beneath  a  copper  plate  which  forms  the  bottom  of  the  central  well 
of  the  water-bath;  the  supply  of  gas  to  the  burner  is  controlled  on 
the  one  hand  by  the  by-pass  tap  B,  on  the  other  hand  by  the  spiral  5. 

The  bath  is  provided  with  an  adjustable  overflow  F;  in  cold  weather 
it  is  only  necessary  to  allow  an  occasional  drop  of  water  to  drip  into 


FIG.  34. 


56  INTRODUCTION. 

the  side  tube  of  the  bath  to  maintain  the  level,  but  in  summer  the  flow 
is  diverted  into  the  bath  itself  and  greatly  increased;  ideal  conditions  are 
reached  when  the  air  temperature  is  up  to  20°  and  the  water  tem- 
perature a  few  degrees  below. 

The  water  circulation  is  maintained  by  means  of  a  rotary  pump 
P  ("Albany"  pump)  which  sucks  the  water  out  of  the  bath  from 
a  point  near  to  the  centre  of  the  regulator,  draws  it  through  the 
various  jackets  and  returns  it  to  the  bath.  In  the  figure  there  are 
shown  (i)  an  ordinary  Schmidt  &  Haensch  jacketed  polarimeter  tube 
/;  (2)  a  copper  water  jacket  K  with  a  removable  lid  Z,,  both  supplied 
with  circulating  water,  designed  to  take  either  of  the  stock  patterns  of 
unjacketed  polarimeter  tubes;  when  not  under  observation  these  can  be 
stored  in  the  bath  itself  in  the  vertical  tubes  V  or,  better,  in  the  hori- 
zontal tubes  H;  the  pump  may  then  be  stopped,  but  a  slight  tempera- 
ture gradient  (0.1°  to  0.2°)  will  appear  in  the  bath  if  the  stirring  is 
also  discontinued.  The  temperature  of  the  return  flow  can  be  read  by 
means  of  a  standard  thermometer  T,  graduated  in  hundredths,  which 
dips  into  a  tube  of  mercury  round  which  the  circulating  water  rapidly 
passes  on  its  way  back  to  the  pump.  The  rubber  bulb  R  serves  to  take 
up  a  part  of  the  thrust  of  the  pump;  it  usually  becomes  flattened,  but 
continues  to  pulsate,  when  the  flow  exceeds  i  litre  per  minute. 

The  pump  is  driven  from  an  electric  motor  M  through  the  gearing  G 
which  carries  the  propeller  and  is  provided  with  several  adjustments. 
The  speed  of  the  motor  is  controlled  by  a  lamp-resistance  not  shown 
in  the  figure.  When  this  resistance  is  short-circuited  the  pump  gives 
a  maximum  flow  of  4  litres  per  minute.  Under  normal  conditions  a 
1 80- volt,  i6-candle-lamp  resistance  on  a  200- volt  circuit  gives  a  flow 
of  about  i  litre  per  minute.  The  temperature  gradient  when  the 
bath  is  at  20°  and  the  room  at  15°  is  about  0.01°  per  jacket. 

When  the  apparatus  described  above  is  used  for  heating  polarime- 
ter tubes  or  refractometer  prisms,  the  temperature  gradient  in  the 
leads  and  jackets  is  reduced  to  a  minimum  by  the  rapid  flow  of 
water  which  can  be  increased  to  any  desired  extent  by  speeding  up 
the  pump  or  increasing  its  size. 

A  simple  form  of  apparatus  made  by  the  Zeiss  comyany  for  keeping 
refractometer  apparatus  at  a  constant  temperature  is  described  under 
Refractometers  (page  29). 

A  simple  thermostat  by  means  of  which  a  sp.  gr.  or  measuring  flask 
can  be  maintained  at  a  definite  temperature,  e.  g.,  15°,  17.5°  or  20°,  is 


ULTIMATE   ANALYSIS. 


57 


constructed  by  taking  a  large  enamelled  iron  cylindrical  saucepan  of 
a  diam.  of  about  15  ins.;  the  water  contained  in  this  is  kept 
at  a  constant  temperature  by  means  of  a  4  in.  diameter  spiral  toluene 
thermo-regulator,  such  as  is  shown  in  Fig  34.  The  water  in  the 
thermostat  is  kept  stirred  by  a  small  paddle,  run  by  a  small  water 
or  electric  motor. 


ULTIMATE  ANALYSIS. 

When  organic  substances  are  heated  to  redness  in  the  air  or  in  the 
presence  of  oxygen-yielding  substances,  they  are  generally  completely 
oxidised,  the  carbon  being  burnt  to  carbon  dioxide  and  the  hydrogen 
to  water.  Nitrogen  is  evolved  for  the  most  part  in  the  free  state,  but 
in  some  cases  partly  in  combination  with  oxygen. 

The  following  general  outlines  may  be  of  service  in  enabling  a 
suitable  method  of  analysis  to  be  chosen. 

Carbon  and  hydrogen  are  estimated  by  igniting  the  substance 
with  dry  copper  oxide  with  or  without  the  assistance  of  a  stream  of 
oxygen.  The  resultant  water  is  absorbed  by  calcium  chloride  and  the 
carbon  dioxide  by  potassium  hydroxide  or 
soda-lime.  In  presence  of  sulphur,  chlorine, 
bromine,  iodine  or  light  metals,  lead  chromate 
is  substituted  for  the  copper  oxide.  Mercury 
is  liable  to  distil  over  into  the  water-absorption 
apparatus.  In  presence  of  nitrogen  the  ante- 
rior part  of  the  tube  is  filled  with  metallic 
copper.  Silver  may  be  substituted  for  the 
copper,  and  has  the  advantage  that  it  retains 
halogens,  but  a  high  temperature  should  be 
employed.  The  Wetzel  potash  bulbs  (Ber., 
1903,  36,  161)  are  strongly  recommended  by 
the  writer  for  the  absorption  of  carbon  dioxide 
(see  Fig.  35),  owing  to  their  remarkable  efficiency.  The  Hill  type  of 
calcium  chloride  tube  (Proc.  Chem.  Soc.,  1906,  22,  87)  is  also  very 
convenient. 

Dennstedt  (Anleitung  zur  Vereinfachung  elementar  Analyse  fur 
wissenschaftliche  und  technische  Zivecke,  1903;  see  the  series  of  papers 
in  the  Berichte,  1897,  30,  1590  and  2861;  Zeit.  anal.  Chem.,  1902, 
41,  525;  1903,  42,  417;  Zeit.  angew.Chem.,  1905,  18,  1134)  has  de- 


FIG.  35. 


58  INTRODUCTION. 

vised  a  method  of  combustion  in  which  the  substance  is  volatilised  in 
oxygen  and  the  combustion  effected  by  the  aid  of  platinised  quartz  or, 
in  the  later  types  of  apparatus,  of  special  platinum  combusters.  The 
great  advantage  of  the  apparatus  is  that  comparatively  little  heating  is 
required  to  burn  the  substance  completely  and  the  use  of  a  furnace  with 
a  large  number  of  burners  is  avoided.  The  method  has  been  still 
further  simplified  by  J.  Walker  and  T.  Blackadder  (Proc.  Royal 
Soc.  Edinb.,  1907-8,  28,  708). 

Nitrogen  may  be  detected  by  heating  the  substance  (if  a  liquid,  ab- 
sorbed by  asbestos  or  sand)  with  metallic  sodium  in  a  narrow  test-tube. 
Cyanide  is  formed,  and  may  be  dissolved  out  with  cold  water.  The 
filtered  liquid  should  be  treated  with  a  drop  each  of  ferrous-sulphate 
and  ferric-chloride  solutions,  and  then  acidified  with  hydrochloric 
acid,  when  a  deep  green  colouration  or  Prussian-blue  precipitate  will 
indicate  that  a  cyanide  was  formed. 

Most  organic  compounds  give  off  the  whole  of  their  nitrogen  in  the 
form  of  ammonia  on  ignition  with  soda-lime.  If  rich  in  nitrogen,  an 
addition  of  sugar  should  be  made  to  the  soda-lime,  on  each  side  of  the 
substance  to  be  analysed,  so  as  to  expel  the  air  as  completely  as 
possible. 

Some  nitrogenised  bodies,  such  as  indigo,  yield  volatile  organic  bases, 
instead  of  ammonia,  on  ignition  with  soda-lime.  These  all  resemble 
ammonia  in  the  fact  that  their  hydrochlorides  form  double  salts  with 
platinum  chloride,  which  on  ignition  leave  194.8  parts  of  platinum 
for  28  of  nitrogen. 

Nitro-substitution  compounds,  such  as  picric  acid,  do  not  evolve 
the  whole  of  their  contained  nitrogen  in  the  form  of  ammonia  when 
ignited  with  soda-lime.  Addition  of  sugar  improves  the  result. 

Cyanogen  compounds  may  be  analysed  by  ignition  with  soda-lime 
if  a  high  temperature  be  ultimately  employed.  The  use  of  sugar  is 
desirable. 

A  general  process  for  the  determination  of  nitrogen  in  organic 
bodies  consists  in  combustion  with  oxide  of  copper,  passing  the  gaseous 
products  over  red-hot  metallic  copper  or  silver,  absorption  of  the  carbon 
dioxide  and  water  by  solution  of  alkali,  and  measurement  of  the  re- 
sidual gaseous  nitrogen,  For  details,  see  (for  example)  Gattermann's 
Praxis  des  Organischen  Chemikers  (7th  Ed.,  Leipzig).  (Practical 
Methods  oj  Organic  Chemistry,  Macmillan.)  V.  Meyer  found  that 
in  the  case  of  nitrogenous  bodies  containing  much  sulphur  it  is  neces- 


ULTIMATE    ANALYSIS.  59 

sary  to  replace  the  oxide  of  copper  by  a  thick  layer  of  lead  chromate, 
and  to  conduct  the  combustion  very  slowly.  The  nitrogen  obtained 
should  be  tested  for  carbon  monoxide.  In  the  case  of  compounds 
containing  methoxyl  and  ethoxyl  groups  the  nitrogen  evolved  may 
contain  large  quantities  of  methane  (see  Haas,  Proc.  Chem.  Soc.,  1906, 
22,  81;  Trans.,  1906,  89,  570). 

Kjeldahl  Method. — For  routine  work  in  organic  analysis,  the 
Kjeldahl  method  is  now  generally  used.  The  original  method  em- 
ployed special  oxidising  agents,  but  in  most  cases  Gunning's  modifi- 
cation is  used.  The  reagents  and  procedure  in  the  standard 
Kjeldahl-Gunning  method  are  as  follows* 

Potassium  Sulphate. — A  coarsely  powdered  form  free  from  ni- 
trates and  chlorides  should  be  selected. 

Sulphuric  Acid. — This  should  have  a  sp.  gr.  1.84  and  be  free  from 
nitrogen  compounds. 

Standard  Acid. — N/2  sulphuric  or  hydrochloric  acid,  the  strength 
of  which  has  been  accurately  determined. 

Standard  Alkali. — N/io  ammonium  hydroxide,  sodium  hydroxide, 
or  barium  hydroxide,  the  strength  of  which  in  relation  to  the  standard 
acid  must  be  accurately  determined. 

Strong  Sodium  Hydroxide  Solution. — Five  hundred  grm.  should 
be  added  to  500  c.c.  of  water,  the  mixture  allowed  to  stand  until  the 
undissolved  matter  settles,  the  clear  liquor  decanted  and  kept  in  a 
stoppered  bottle.  It  will  be  an  advantage  to  determine  approxi- 
mately the  quantity  of  this  solution  required  to  neutralise  20  c.c.  of  the 
strong  sulphuric  acid. 

Indicator. — Cochineal  solution  is  recommended  by  the  A.  O.  A.  C., 
but  methyl-orange,  azolitmin,  and  sodium  alizarinmonosulphonate 
are  satisfactory.  Phenolphthalein  is  not  well  adapted  to  titration 
of  ammonium  compounds. 

Combined  Digestion  and  Distillation  Flasks. — Jena-glass  round- 
bottomed  flasks  with  a  bulb  12.5  cm.  long  and  9  cm.  in  diameter,  the 
neck  cylindrical,  15  cm.  long  and  3  cm.  in  diameter,  flared  slightly  at 
the  mouth. 

Process. — From  0.7  to  3.5  grm.,  according  to  the  proportion  of 
nitrogen,  are  placed  in  a  digestion  flask.  Then  10  grm.  of  powdered 
potassium  sulphate  and  15  to  25  c.c.  (ordinarily  about  20  c.c.)  of  the 
strong  sulphuric  acid  are  added  and  the  digestion  conducted  as  fol- 
lows: The  flask  is  placed  in  an  inclined  position  and  heated  below  the 


<5o 


INTRODUCTION. 


b.  p.  of  the  acid  during  from  5  to  15  minutes,  or  until  frothing  has 
ceased.  Excessive  frothing  may  be  prevented  by  the  addition  of  a 
small  piece  of  paraffin.  The  heat  is  raised  until  the  acid  boils  briskly. 
A  small,  short-stemmed  funnel  may  be  placed  in  the  mouth  of  the 
flask  to  restrict  the  circulation  of  air.  No  further  attention  is  required 
until  the  liquid  has  become  clear  and  colourless  or  not  deeper  than  a 
pale  straw-colour. 

When  Kjeldahl  operations  are  carried  out  in  limited  number,  the 
arrangement  shown  in  Fig.  36  is  satisfactory."  A  double- Y,  terra- 
cotta drain-pipe,  about  20  cm.  internal  diameter,  is  connected  by  an 


FIG.  36. 


FIG.  37. 


-elbow  directly  with  the  chimney-stack.  The  digestion  flasks  are  sup- 
ported as  shown  in  a  rough  sketch  (not  drawn  exactly  to  scale).  Two 
flasks  can  be  operated  at  once.  The  central  opening  is  convenient 
ior  other  operations  producing  fumes.  Openings  not  in  use  are  closed 
by  circles  of  heavy  asbestos. 

The  apparatus  shown  in  Fig.  37  is  used  when  many  determinations 
are  made.  As  corrosive  vapours  are  given  off,  it  must  be  placed  under 
a  hood.  The  central  opening  in  the  ventilating  pipe  shown  in  Fig. 
36  will  be  satisfactory;  the  mouths  of  the  flasks  should  be  well  inside 
the  margin  of  the  pipe. 

When  the  liquid  has  become  colourless  or  very  light  straw-yellow,  it  is 
allowed  to  cool,  and  diluted  by  the  cautious  addition  of  200  c.c.  of  water. 
•Granulated  zinc,  pumice-stone,  or  0.5  grm.  of  zinc  dust  is  added. 


ULTIMATE   ANALYSIS. 


6l 


50  c.c.  of  the  strong  sodium  hydroxide  solution,  or  sufficient  to  make 
the  reaction  strongly  alkaline,  should  be  slowly  poured  down  the  side 
of  the  flask  so  as  not  to  mix  at  once  with  the  acid  solution.  It  is  con- 
venient to  add  to  the  acid  liquid  a  few  drops  of  the  indicator  solution, 
to  show  when  the  liquid  is  alkaline,  but  it  must  be  noted  that  strong 
alkaline  solutions  destroy  some  indicators.  The  flask  is  shaken  so  as 
to  mix  the  alkaline  and  acid  liquids  and  at  once  attached  to  the  con- 
densing apparatus.  The  receiving  flask  should  have  been  previously 
charged  with  a  carefully  measured  volume  of  the  N/2  acid  (loc.c.  di- 
luted with  water  to  100  c.c.  is  a  convenient  amount).  A  few  drops  of 
the  indicator  solution  should  also  be  added.  The  distillation  is  con- 
ducted until  about  150  c.c.  have  passed  over.  The  acid  is  then, 
titrated  with  standard  alkali,  and  the  amount  neutralised  by  the  dis- 
tilled ammonia  determined  by  subtrac- 
tion. Each  c.c.  of  N/2  acid  neutralised 
is  equivalent  to  0.007  nitrogen. 

The  distillation  in  this  operation  re- 
quires care,  as  the  amount  of  ammonia 
formed  is  determined  by  its  neutralising 
power,  hence  solution  by  the  alkali  of 
the  glass  will  introduce  error.  Common 
glass  is  not  satisfactory.  Block-tin  is 
the  best  material  for  the  Kjeldahl- 
Gunning  form,  but  Moerrs  has  shown 
that  it  is  not  adapted  to  the  methods  in 
which  mercury  oxide  is  employed.  He 
found  that  Jena-glass  tubes  resist  the 
action  of  the  alkali.  The  distillates 
should  be  titrated  promptly;  on  standing 
for  some  hours  some  alkali  may  be 
taken  up  from  the  flask. 

The  most  satisfactory  condensing  arrangement  for  general  laboratory 
use  is  a  copper  tank  of  good  size,  through  which  several  condensing 
tubes  pass.  Such  an  arrangement  as  applied  to  Kjeldahl  distil- 
lations is  shown  in  Fig.  38,  which  is  a  rough  sketch,  not  drawn  to- 
scale.  The  flask  is  the  standard  Jena-glass  distilling  flask,  about  12 
cm.  diameter,  the  tank  .should  be  high  enough  to  allow  of  a  condensing 
tube  60  cm.  long.  The  connection  of  this  with  the  receiving  flask  is 
made  by  means  of  a  bulb  tube  to  allow  for  occasional  drawing  back 


FIG.  38. 


62 


INTRODUCTION. 


of  the  liquid.  The  cork  through  which  this  tube  passes  into  the  flask 
must  not  fit  closely,  as  opportunity  must  be  given  for  expansion  of  the 
air.  The  safety-tube  connecting  the  distilling  flask  with  the  condenser 
should  terminate  a  little  below  the  water  level  in  the  tank.  The  appa- 
ratus may  be  satisfactorily  heated  by  a  low-temperature  burner.  To 
avoid  spurting  of  the  boiling  liquid,  it  is  usual  to  interpose  a  safety 
tube  between  the  distilling  flask  and  the  condenser.  Many  forms  have 
been  suggested.  That  shown  in  Fig.  39  is  most  in  use. 

In  some  analyses  (as  in  the  case  of  pepper) 
the  Kjeldahl-Gunning  method  must  be  replaced 
by  Arnold's  modification:  One  grm.  of  the 
sample  is  mixed  with  i  grm.  of  crystallised 
copper  sulphate  and  i  grm.  of  mercuric  oxide. 
The  potassium  sulphate-sulphuric  acid  mixture 
as  given  above  is  added  and  the  mass  heated 
cautiously  until  frothing  ceases,  when  the  temper- 
ature is  raised  and  the  digestion  completed.  The 
liquid  is  diluted  for  distillation,  50  c.c.  of  a  solu- 
tion of  commercial  potassium  sulphide  (40  grm. 
to  1000  c.c.)  are  added,  and  sufficient  sodium 
hydroxide  as  usual.  The  liquid  is  liable  to  bump. 
Modification  for  Nitrates. — If  nitrates  are 
present  in  the  material,  the  weighed  sample  is 
well  mixed  w^th  35  c.c.  of  sulphuric  acid  contain- 
ing 2%,  by  weight,  of  salicylic  acid,  and  the  mass  shaken  frequently 
during  10  minutes;  5  grm.  of  sodium  thiosulphate  are  added  and  10 
grms.  of  potassium  sulphate.  The  mixture  is  heated  very  gently  until 
frothing  ceases  and  then  according  to  the  usual  method.  The  nitro- 
gen in  the  distillate  will  include  that  derived  from  the  nitrogen  of  the 
nitrates. 

Chlorine,  bromine  and  iodine  are  detected  in  an  organic  substance 
by  heating  it  with  metallic  sodium  in  a  small  glass  tube,  dropping  the 
tube,  while  hot,  into  distilled  water,  filtering  the  so  ution  so  obtained 
from  the  fragments  of  glass  and  testing  with  silver  nitrate  after  acidi- 
fying with  pure  nitric  acid.  If  nitrogen  is  present  in  the  compound 
silver  cyanide  is  formed  in  the  above  process;  in  such  cases  it  is  best  to 
heat  a  little  of  the  substance  with  pure  lime  in  place  of  the  sodium  in 
the  above  test  and,  after  dissolving  the  product  in  pure  dilute  nitric 
acid,  to  test  for  the  halogen  in  the  solution.  The  halogens  are  best  es- 


FIG.  39. 


ULTIMATE    ANALYSIS.  63 

timated  by  Carius'  method  which  consists  in  completely  oxidising  the 
substance  by  heating  it  with  fuming  nitric  acid  (of  sp.  gr.  1.5)  in  a  sealed 
tube  containing  about  1.5  times  the  theoretical  quantity  of  silver 
nitrate.  The  method  is  described  in  most  text-books  of  practical  or- 
ganic chemistry  (e.  g.,  Gattermann's  Practical  Methods  of  Organic 
Chemistry)  and  is  very  accurate.  In  most  cases  the  decomposition 
of  the  compound  is  complete  after  heating  6  hours  at  200-205°  C.; 
but  it  is  safest  to  heat  the  tube,  after  releasing  the  pressure, 
during  another  6  hours  at  250-300°,  so  as  to  insure  complete 
decomposition. 

Plimpton  and  Groves  determine  the  halogens  in  volatile  organic 
bodies  by  burning  the  substance  gradually  in  a  bunsen  flame,  placed 
under  a  trumpet-shaped  tube,  and  absorbing  the  products  of  com- 
bustion in  solution  of  sodium  hydroxide  which  is  subsequently 
acidified  with  nitric  acid  and  precipitated  by  silver  nitrate.  The  test 
analyses  by  this  method  are  highly  satisfactory,  and  the  process  is  rapid 
and  simple. 

Sulphur,  Phosphorus  and  Arsenic  may  be  detected  by  igniting 
the  substance  with  pure  soda-lime  mixed  with  an  exidising  agent, 
such  as  potassium  chlorate,  mercuric  oxide,  or  sodium  peroxide.  The 
residue  is  tested  for  sulphates,  phosphates  and  arsenates.  The  process 
may  be  made  quantitative.  Another  method  is  to  heat  the  substance 
in  a  sealed  tube  with  nitric  acid  of  1.5  sp.  gr.  The  sulphur,  phos- 
phorus and  arsenic  are  converted,  respectively,  into  sulphuric,  phos- 
phoric and  arsenic  acids.  Sulphur  is  also  easily  recognised  in  the 
solution  obtained  by  heating  the  substance  with  sodium  in  testing  for  a 
halogen;  it  is  only  necessary  to  put  a  drop  of  the  solution  on  a  silver 
coin  when,  if  sulphur  is  present,  the  coin  is  blackened  owing  to  the 
formation  of  silver  sulphide. 

Sulphur,  phosphorus  and  arsenic  are  readily  estimated  by  oxidis- 
ing the  substance  with  nitric  acid,  as  in  Carius'  method,  this  treat- 
ment giving  rise  to  sulphuric  acid,  phosphoric  acid  and  arsenic  acid, 
respectively.  (See  page  146.) 

Metals  usually  remain  in  the  residue  obtained  on  igniting  the  organic 
substance  in  the  air.  Metals  of  the  alkalies  and  alkaline  earths  are 
usually  left  as  carbonates,  but  when  sulphonic  groups  are  present 
sulphates  are  formed;  phosphates  or  haloids  may  be  formed  when 
phosphorus  or  halogens  are  present.  Heavy  metals  are  usually  left  as 
oxides,  except  silver,  gold  and  platinum,  which  will  remain  in  the  free 


64  INTRODUCTION. 

state.  Arsenic,  antimony  and  other  metals,  when  existing  in  volatile 
compounds,  may  be  completely  volatilised.  (See  page  74.) 

Mercury  will  usually  be  wholly  volatilised.  It  may  be  estimated 
'in  all  instances  by  igniting  the  substance  with  soda-lime,  and  collecting 
and  weighing  the  mercury  which  distils  over. 

Oxygen  may  be  detected  by  ignition  of  the  substance  in  a  stream  of 
hydrogen,  when  water  will  be  formed.  By  igniting  the  substance 
in  a  stream  of  chlorine,  or  in  admixture  with  potassium  chloroplatinate, 
carbon  dioxide  will  be  formed  if  oxygen  be  present.  Hydrochloric  acid 
and  chlorine  may  be  respectively  absorbed  by  solutions  of  lead  nitrate 
and  stannous  chloride,  and  the  carbon  dioxide  passed  into  baryta 
water  or  potassium-hydroxide  solution.  In  the  great  majority  of  cases 
the  oxygen  of  organic  bodies  is  determined  "by  difference." 

MOISTURE,  CRUDE  FIBRE  AND  ASH. 

These  are  data  of  proximate  analysis,  frequently  required  in  con- 
nection with  commercial  organic  analysis. 

Moisture  may  be  either  hygroscopic  or  molecular.  The  former  is 
always  influenced  by  atmospheric  conditions,  the  latter  not  usually. 
In  most  cases  in  commercial  organic  analysis,  the  hygroscopic  moisture 
is  alone  important.  In  ordinary  cases  the  operation  is  conducted  in  a 
water-  or  air-oven  at  atmospheric  pressure,  but  vacuum  drying  ovens 
are  now  much  used,  and  for  some  analyses  an  atmosphere  of 
hydrogen  is  necessary.  Soxhlet's  oven,  in  which  a  solution  of  common 
salt  in  water  is  used,  permits  of  the  employment  of  a  temperature 
slightly  higher  than  100°. 

Moisture  is  usually  estimated  with  sufficient  accuracy,  provided 
other  volatile  bodies  are  not  present,  by  heating  the  material  (solids 
should  be  finely  divided)  in  a  flat  dish  on  the  water-bath  or  in  the  water- 
oven  until  it  ceases  to  lose  weight.  Flat  platinum  dishes  from  4  to  8  cm. 
in  diameter  and  0.5  cm.  high  are  well  adapted  to  this  work  They 
should  rest  on  porcelain  or  asbestos  rings.  Nickel  dishes  are  often  ap- 
plicable, especially  the  broad  shallow  crucible  covers  made  in  dish  form. 
Dishes  of  glass — especially  the  shallow  (petri)  dishes  used  for  microbe 
culture — and  porcelain  are  suitable;  aluminum  and  tin  less  so.  The 
drying  of  a  liquid  will  be  facilitated  by  using  an  absorbent  material,  such 
as  pure  quartz  sand,  powdered  asbestos  or  pumice-stone.  These  mate- 
rials should  be  extracted  with  dilute  hydrochloric  acid,  well  washed  and 


MOISTURE.  65 

well  dried  before  use.  The  quantity  used  should  be  rapidly  weighed, 
preferably  in  the  dish  in  which  the  operation  is  to  be  carried  out.  It 
is  advisable  to  cover  the  dish  with  a  nearly  flat,  thin  watch-glass  in  all 
the  weighings.  By  a  few  trials  a  glass  can  be  selected  which  fits  fairly 
close  to  the  rim  of  the  dish  and  restricts  evaporation  or  absorption  of 
water.  It  is  often  convenient  to  wreigh  a  small  stirring-rod  with  the 
dish  and  absorbent. 


FIG.  40. 

In  many  cases  a  liquid  can  be  measured  directly  into  the  dish,  the 
residue  being  recorded  in  grm.  per  100  c.c.  or  other  suitable  ratio. 

Syrupy  and  gelatinous  liquids  or  those  containing  much  solid  matter, 
especially  if  this  be  somewhat  difficult  to  dry,  may  often  be  more 
satisfactorily  treated  by  diluting  a  weighed  portion  with  several  times 
its  weight  of  water,  evaporating  a  measured  or  weighed  amount  of 
the  dilute  liquid,  and  calculating  the  amount  of  residue  in  the  original 
substance. 

Vol.  I.— 5 


66  INTRODUCTION. 

The  ordinary  water-bath  and  water-oven  need  no  description.  The 
temperature  of  materials  heated  on  the  former  is  usually  much  less  than 
100°;  in  the  latter,  slightly  below  100°. 

The  following  are  some  convenient  special  forms  of  drying  oven: 

Fig.  40  shows  a  drying  oven  for.  use  with  a  current  of  hydrogen.  The 
apparatus  was  designed  by  Caldwell  for  estimatning  moisture,  ether- 
extract,  and  crude  fibre  as  prescribed  by  the  A.  O.  A.  C.,  the  three  data 
being  determined  on  the  same  sample. 

The  bath  is  made  of  copper  and  is  24  cm.  long,  15  high,  and  8.5 
broad.  It  stands  in  a  piece  of  sheet-copper  bent  at  right  angles  along 
the  sides,  as  shown  in  the  end  view;  on  one  side  this  vertical  part  need 
not  be  over  i  cm.  high,  just  enough  to  project  a  little  up  the  side  of  the 
bath,  which  rests  snugly  against  it;  along  the  other  side  it  projects  up- 
wards, at  a  little  distance  from  the  side  of  the  bath,  about  15  mm.,  and 
to  about  the  height  of  4  cm. ;  opposite  each  of  the  tubes  of  the  bath  a 
slot  is  cut  in  this  vertical  part,  which  serves  then  as  a  shoulder  against 
which  the  glass  tube  rests  when  in  place,  to  keep  it  from  slipping  down 
and  out  of  position. 

The  tube  for  containing  the  substance  has  at  the  zone  a  three  small 
projections  on  the  inner  surface,  which  support  a  perforated  platinum 
disc  of  rather  heavy  platinum  foil  carrying  the  asbestos  filter.  This 
tube  is  13  cm.  long  and  23  mm.  inner  diameter,  and  weighs,  with  its 
closed  stoppers,  about  30  grm. 

The  filter  is  readily  made  in  the  same  manner  as  the  gooch  filter, 
the  tube  being  first  fitted  to  a  suction  flask  by  an  enlargement  of  one  of 
the  holes  of  the  rubber  cork  or,  better  still,  by  slipping  a  short  piece  of 
rubber  tube  over  it,  of  such  thickness  that  it  will  fit  tightly  in  the  mouth 
of  a  suction  flask  provided  with  a  lateral  tube  for  connection  with  the 
suction.  A  thin  layer  of  asbestos  is  sufficient;  if  it  is  too  thick,  the  gas 
and  ether  will  not  flow  through  readily. 

About  2  grm.  of  the  substance  are  put  in  this  tube,  previously 
weighed  with  the  stoppers  b  and  c,  and  the  weight  of  the  substance  accu- 
rately determined  by  weighing  tube  and  contents.  The  stoppers  are  re- 
moved, a  band  of  thin  asbestos  paper  is  wound  around  the  end  d  of  the 
tube,  a  little  behind  the  slight  shoulder  at  the  rim,  as  many  times  as  may 
be  necessary  to  make  a  snug  fit,  when  this  tube  is  slid  down  into  the 
copper  tube  in  the  bath,  thus  preventing  circulation  of  air  between  the 
glass  and  the  copper  tubes  that  would  retard  the  heating  of  the  former; 
the  stopper  e  is  put  in  the  lower  end  of  the  tube  for  connection  with  the 


MOISTURE.  67 

hydrogen  supply,  and  the  stopper/ in  the  upper  end;  this  latter  stopper 
is  connected  by  rubber  tube  with  a  glass  tube  slipping  easily  through 
one  of  the  holes  of  a  rubber  cork  closing  a  small  flask,  containing  a 
little  sulphuric  acid,  into  which  this  tube  just  dips;  when  as  many  tubes 
as  are  to  be  charged  are  thus  arranged  in  place  and  the  hydrogen  is 
turned  on,  the  even  flow  of  the  current  through  the  whole  number  is 
secured  by  raising  or  lowering  a  very  little  the  several  tubes  through 
which  the  outflow  passes,  so  as  to  get  a  little  more  back  pressure  for  one, 
or  a  little  less  for  another,  as  may  be  found  necessary.  When  the  dry- 
ing is  supposed  to  be  completed,  the  tubes  are  weighed  again  with  their 
closed  stoppers,  and  so  on. 

For  ether-extraction  the  unstoppered  tube  with  contents  is  put 
directly  into  the  extractor. 

Carr  and  Osborne  have  made  an  extended  series  of  investigations  as 
to  the  estimation  of  water,  and  find  that  more  accurate  results 
may  be  obtained  if  the  operation  be  conducted  under  a  diminished 
pressure  at  a  temperature  not  exceeding  70°.  Under  these  conditions 
it  was  found  possible  to  dehydrate  laevulose  completely  without  de- 
composition. The  oven  is  made  of  a  section  of  metal  tubing,  from  15 
to  20  cm.  in  diameter  and  30  to  40  cm.  long.  One  end  is  closed  air- 
tight by  a  brass  end-piece,  brazed  or  attached  by  a  screw.  The  other 
end  is  detachable  and  is  made  air-tight  by  ground  surfaces  and  a  soft 
washer.  On  the  top  are  apertures  for  the  insertion  of  a  vacuum-gauge 
and  for  attachment  to  a  vacuum-apparatus,  thermostat  and  thermom- 
eter. The  aperture  for  admission  of  air  or  hydrogen  is  best  placed  at 
the  fixed  end.  The  oven  may  be  heated  by  a  single  burner,  but  a  series 
of  small  jets  is  preferable.  The  metal  should  be  protected  by  sheet 
asbestos.  The  temperature  of  the  oven  can  be  kept  uniform  by  a  gas 
regulator  or  by  attention  to  the  lamp  (see  page  69). 

The  method  of  operating  is  as  follows:  Clean  pumice-stone  of 
two  grades  of  fineness  is  used,  one  that  just  passes  through  a  i  mm. 
mesh  and  one  that  passes  through  a  6  mm.  mesh.  These  are  digested 
with  hot  2%  sulphuric  acid,  washed  by  decantation  until  the  wash-water 
is  free  from  acid,  placed,  wet,  in  a  sand  crucible  and  heated  to  redness. 
When  the  water  is  expelled,  the  material  may  either  be  placed  hot  into  a 
desiccator  or  directly  into  the  drying  dishes.  In  loading  the  dishes, 
place  a  thin  layer  of  dust  over  the  bottom  of  the  dish  to  prevent  the 
material  to  be  dried  from  coming  in  contact  with  the  metal;  over  this 
layer  place  the  larger  particles,  nearly  filling  the  dish.  If  the  stone  has 


68  INTRODUCTION. 

been  well  washed,  no  harm  can  result  from  placing  the  dish  and  stone 
over  the  flame  for  a  moment  before  transferring  to  the  desiccator  pre- 
paratory to  weighing. 

If  the  material  to  be  dried  is  a  thick  liquid,  it  is  diluted  until  the 
sp.  gr.  is  in  the  neighbourhood  of  1.08  by  dissolving  a  weighed  quantity 
in  a  weighed  quantity  of  water.  (Alcohol  may  be  substituted  in  the  case 
of  material  not  precipitable  thereby.)  Of  this,  2  to  3  grm.  may  be  dis- 
tributed over  the  stone  in  a  dish  the  area  of  which  is  in  the  neighbour- 
hood of  20  sq.  cm.,  or  i  grm.  for  each  7  sq.  cm.  of  area.  The  material 
is  distributed  uniformly  over  the  pumice  by  means  of  a  pipette 
weighing-bottle  (weighing  direct  upon  pumice  will  not  answer),  ascer- 
taining the  weight  taken  by  difference. 

The  dishes  are  placed  in  the  oven,  which  should  be  maintained  at  a 
pressure  of  not  more  than  125  mm.  of  mercury.  The  temperature  must 
not  exceed  about  70°.  All  weighings  must  be  taken  with  the  dish  cov- 
ered by  a  close-fitting  plate.  The  open  dish  must  not  be  exposed  to  the 
air  longer  than  absolutely  necessary.  Weighings  may  be  made  at 
intervals  of  from  2  to  3  hours. 

In  the  laboratory  of  the  United  States  Geological  Survey  a  sheet- 
iron  or  nickel  basin  about  10  cm.  in  diameter  and  3  cm.  deep  is  set  upon 
an  iron  plate  which  is  heated  directly  by  the  burner.  A  platinum  or 
pipe-clay  triangle  rests  in  the  basin  and  supports  the  dish  containing 
the  liquid  to  be  evaporated.  It  is  stated  that  almost  any  liquid  can  be 
evaporated  in  this  way  without  sputtering.  The  temperature,  however, 
is  liable  to  be  too  high  for  many  organic  bodies. 

Parsons  has  obtained  good  results  in  the  drying  of  sensitive  organic 
substances  by  the  following  method:  A  perfectly  neutral  petroleum 
oil,  free  from  animal  or  vegetable  oils  and  mineral  substances,  sp.  gr. 
0.920,  flash  test  224°,  fire  test  260°,  b.  p.  about  288°,  is  heated  to  about 
120°  for  some  time  and  preserved  in  a  well-stoppered  vessel.  A 
quantity  of  oil  about  6  times  that  of  the  weight  of  the  substance  to  be 
dried  is  heated  in  an  evaporating  dish  in  a  drying  oven  to  a  temperature 
of  115°,  and  then  weighed.  The  weighed  portion  of  the  substance  is 
put  into  the  oil;  if  it  be  very  moist,  it  is  added  in  small  portions.  Slight 
effervescence  will  usually  occur,  and  the  mass  should  be  kept  in  the 
drying  oven  for  a  short  time  after  effervescence  has  ceased.  The 
evaporating  dish  containing  the  oil  and  substance  is  weighed;  the  loss 
is  moisture.  The  whole  operation  may  be  completed  in  less  than  half 
an  hour. 


MOISTURE. 


69 


CONSTANT    TEMPERATURE     OVENS. 

An  approximately  constant  temperature  can  be  maintained  in  an 
ordinary  hot-air  oven  heated  by  gas,  by  controlling  the  supply  of  gas 
by  means  of  a  suitable  thermo-regulator,  e.  g.,  a  Reichert  mercury 
regulator  of  the  type  shown  in  Fig.  41. 

A  vapour  bath  such  as  that  devised  by  Victor 
Meyer  and  shown  in  Fig.  42,  is  often  convenient 
for  drying  a  substance  at  a  known  constant  tem- 
perature; with  such  a  bath 

almost  any  definite  temperature 

can  be  maintained  by  choosing 

a  suitable  liquid  to  be  vapour- 

ised  in  the  outer  jacket.     For 

example,  chloroform,  petroleum, 

benzene,  toluene,  xylene,  aniline, 

naphthalene    give    a    series   of 

definite  temperatures  on  a  rising 

.scale.      The   same  principle   is 

applied  in  the  Abati  drying  oven 

( Vereinigte  Fabriken  f  iir  Labora- 

toriums-bedarf)  shown  in  Fig.  43. 
A    suitable    solvent    is    kept 

vigorously  boiling  in  the   flask 

below  the  oven  by  means  of  the 

bunsen  burner.     With  this  ap- 
FIG.  41.          paratus  it  is  very  easy  to  change  FIG.  42. 

from  one  constant  temperature  to  another  by  simply  changing  the 
flask  and  solvent. 

Several  types  of  ovens  heated  by  electricity  are  also  in  use. 


VACUUM    DRYING    OVENS. 

In  organic  analysis  it  is  often  convenient  to  dry  a  substance  in  a 
vacuum  at  a  lower  temperature  than  the  b.  p.  of  the  solvent  impreg- 
nating the  substance.  A  convenient  form  of  apparatus  for  drying 
in  a  vacuum  (Siderski,  Zeit.  anal.  Chem.,  1890,  280)  is  shown  in 
Fig.  45;  it  is  made  by  the  V.  F.  f.  L.  An  arrangement  made  by 
the  same  firm  for  evaporating  in  a  vacuum  is  shown  in  Fig.  44 


7o 


INTRODUCTION. 


FIG.  43. 


FIG.  44. 


Crude  Fibre. — The  proximate  constituents  included  in  this  term 
are  principally  forms  of  cellulose,  but  the  method  given  herewith, 
which  is  that  of  the  A.  O.  A.  C.  yields  a  residue  containing  notable 
amounts  of  other  substances: 

2  grm.  of  the  substance,  well  extracted  with  ether  (see  under  "Ex- 
traction"), are  mixed  in  a  500  c.c.  flask  with  200  c.c.  of  boiling  water 
containing  1.25%  of  sulphuric  acid;  the  flask  is  connected  with  an 
inverted  condenser,  the  tube  of  which  passes  only  a  short  distance 
below  the  rubber  stopper  of  the  flask.  The  liquid  is  brought  to  the 
b.  p.  as  rapidly  as  possible  and  maintained  there  for  30  minutes. 
A  blast  of  air  conducted  into  the  flask  may  serve  to  reduce  the  froth- 


CRUDE    FIBRE.  71 

ing  of  the  liquid.  The  mass  is  filtered,  washed  thoroughly  with 
boiling  water  until  the  washings  are  no  longer  acid;  the  undissolved 
substance  rinsed  back  into  the  same  flask  with  the  aid  of  200  c.c.  of 
boiling  water  containing  1.25%  of  sodium  hydroxide  nearly  free  from 
sodium  carbonate;  again  brought  to  the  b.  p.  rapidly  and  maintained 
there  for  30  minutes  as  directed  above. 


C(f 


FIG.  45. 

The  liquid  is  filtered  by  means  of  a  gooch  crucible;  washed  with 
boiling  water  until  the  washings  are  neutral  to  phenolphthalein;  dried 
at  110°;  weighed  and  then  incinerated  completely  and  again  weighed. 
The  loss  of  weight  is  crude  fibre. 

The  filters  used  for  the  first  filtration  may  be  linen,  glass,  wool,  asbes- 
tos, or  any  form  that  secures  clear  and  reasonably  rapid  filtration.  Har- 
dened-paper filters  may  serve.  The  sulphuric  acid  and  sodium  hydrox- 


72  INTRODUCTION. 

ide  must  be  made  up  of  the  specified  strength,  determined  by  titration. 
The  material  must  be  ground  very  fine  and  the  preliminary  extraction 
with  ether  must  not  be  omitted.  It  is  probable  that  carbon  tetrachlor- 
ide  could  be  advantageously  substituted  for  ether  in  the  preliminary 
extraction. 

Crude  fibre  should  not  be  called  cellulose. 

Ash. — The  method  of  detecting  and  estimating  the  mineral  constit- 
uents of  an  organic  substance  usually  consists  simply  in  igniting  a 
known  weight  of  the  body  in  free  contact  with  the  air,  and  weighing 
the  residue  or  ash. 

The  most  satisfactory  method  of  estimating  the  ash  of  organic 
substances  is  to  conduct  the  ignition  in  a  platinum  tray,  or  flat  capsule 
placed  in  a  gas-muffle  maintained  at  the  lowest  temperature  compatible 
with  combustion.  The  tray  should  be  supported  on  a  row  of  pieces  of 
tobacco-pipe  stem  or  other  non-conducting  substance,  so  as  to  avoid 
over-heating  from  contact  with  the  bottom  of  the  muffle.  If  a  bunsen 
burner  is  employed  to  effect  combustion,  similar  care  should  be  taken 
to  avoid  over-heating.  If  too  high  a  temperature  is  employed  there 
is  great  danger  of  loss  by  volatilisation  of  chlorides  or  carbonates  and 
additional  trouble  may  arise  from  fusion  of  the  remaining  ash,  with 
consequent  enclosure  of  particles  of  unburnt  carbon.  By  keeping 
the  temperature  as  low  as  possible,  and  avoiding  local  heating, 
nearly  all  organic  substances  can  be  burnt  completely  and  without 
difficulty.  In  obstinate  cases,  the  unconsumed  matter  may  be  mixed 
with  ammonium  nitrate  or  moistened  with  a  strong  solution  of  the 
salt  and  then  reignited.  Addition  of  pure  mercuric  oxide  is  also 
useful  occasionally,  or  the  refractory  matter  may  be  mixed  with  a 
known  weight  of  dry  ferric  oxide  and  again  ignited. 

In  very  many  instances  the  difficulty  of  effecting  complete  com- 
bustion and  the  danger  of  loss  by  volatilisation  may  be  wholly  over- 
come by  moistening  the  substance  to  be  ignited,  or  the  carbonaceous 
residue  therefrom,  with  strong  sulphuric  acid.  This  converts  the  readily 
fusible  and  volatile  chlorides  and  carbonates  into  the  more  fixed  sul- 
phates of  the  alkali  metals,  and  on  ignition  complete  combustion  will 
readily  ensue.  This  method  is  used  in  ascertaining  the  percentage  of 
metal  in  sulphonates  and  some  other  salts.  It  is  necessary  to  moisten 
the  ash  with  a  drop  of  sulphuric  acid  and  reignite,  so  as  to  get  rid  of 
any  sulphides  left  after  the  first  ignition.  For  obtaining  the  ash  of 
animal  matters,  it  is  desirable  to  treat  the  substance  in  a  porcelain 


ASH.  73 

crucible  with  a  mixture  of  strong  nitric  and  sulphuric  acids.  This 
dissolves  and  destroys  the  organic  matters  before  ignition,  and,  on 
evaporating  the  liquid  to  dryness  and  igniting  the  residue,  complete 
combustion  ensues,  and  a  white  "sulphated  ash"  is  readily  obtained. 
The  same  modification  of  the  usual  method  of  determining  the  ash  of 
plants  may  be  pursued  with  advantage  in  many  cases,  the  starch  and 
cellulose  being  first  converted  into  oxalic  acid,  which  the  sulphuric 
acid  decomposes  into  carbon  oxides  and  water,  so  that  after  evapo- 
ration of  the  acid  there  is  but  little  organic  matter  left  to  ignite. 

Sulphuric  acid  is  almost  always  employed  in  determining  the  ash  of 
commercial  sugars,  a  deduction  being  made  from  the  weight  obtained 
for  the  increase  due  to  "sulphation." 

Besides  being  in  excess  of  the  true  ash,  the  "sulphated  ash"  will 
contain  no  chlorides  or  carbonates.  Phosphoric  and  silicic  acids  are 
not  affected  by  the  treatment. 

The  estimation  of  ash  may  be  facilitated  by  igniting  the  charred 
residue  in  a  current  of  oxygen.  The  complete  combustion  of  the  car- 
bon is  frequently  prevented  by  the  formation  of  a  glaze  of  fused  mineral 
matter.  In  many  cases  this  difficulty  may  be  avoided  by  allowing 
the  charred  mass  to  cool,  washing  it  with  distilled  water  and  collecting 
the  washing  through  a  small,  nearly  ashless  filter;  the  washed  residue 
is  then  burned  white,  the  watery  solution  added,  and  evaporated  to 
dryness. 

It  must  be  remembered,  however,  that  carbonate  in  the  ash  is  usually 
the  skeleton  of  the  salts  of  organic  acids  present  in  the  original  sub- 
stance. Many  analysts  deduct  the  carbon  dioxide  in  the  ash  from  the 
total  weight  obtained,  and  report  the  difference  as  "true  ash."  A 
similar  correction  is  often  made  for  the  "sand  and  carbon"  left  on 
treating  the  ash  with  dilute  acid,  the  sand  being  merely  an  accidental  im- 
purity and  not  a  true  constituent  of  the  plant,  and  the  carbon  being 
simply  due  to  incomplete  combustion  of  the  organic  matter. 

The  ordinary  constituents  of  the  ash  of  natural  organic  sub- 
stances are  potassium,  sodium,  calcium,  magnesium,  manganese  and 
iron  which  exist  as  oxides,  carbonates,  sulphates,  phosphates,  silicates 
and  chlorides.  Traces  of  other  elements  exist  normally  in  certain  cases, 
but  the  foregoing  are  those  to  which  attention  is  generally  directed.  In 
algae  notable  traces  of  bromides  and  iodides  occur,  while  some  other 
cryptogams  contain  aluminum.  Common  flowering  plants  and  animal 
tissues  used  for  human  food  do  not  contain  appreciable  amounts  of 


74  INTRODUCTION. 

aluminum,  but  clay  being  a  common  ingredient  of  soils,  aluminum 
compounds  may  be  present  as  adventitious  material.  Copper  is 
widely  distributed,  occurring  in  minute  amount  in  wheat  flour  and 
some  of  the  viscera  (e.  g.,  liver)  of  domestic  animals.  It  is  a  constant 
ingredient  of  the  circulating  fluid  of  the  lobster.  Lately,  barium  has 
been  found  as  a  notable  ingredient  in  the  ash  of  some  plants  from  the 
cattle  feeding  districts  of  the  western  United  States.  It  has  also  been 
found  in  Egyptian  wheat.  Zinc  is  present  in  a  few  rare  cases. 

Analysis  of  Ash. —  Ash  analysis  may  be  effected  by  the  ordi- 
nary methods  of  mineral  analysis,  but  it  should  be  borne  in  mind 
that  the  ash  of  wheat  and  other  cereals  is  apt  to  contain  pyrophosphates 
and  these  must  be  converted  into  orthophosphates  by  fusing  the  ash 
with  alkaline  carbonate  before  the  ordinary  process  for  phosphoric 
acid  can  be  employed.  Titration  of  chlorine  by  silver  nitrate  solution 
(with  potassium  chromate  as  indicator)  cannot  be  effected  with  accu- 
racy, unless  the  phosphates  have  been  previously  removed  by  precipi- 
tating tbe  aqueous  solution  of  the  ash  with  calcium  nitrate. 

In  many  cases  it  is  of  service  to  ascertain  the  proportion  of  the  total 
ash  which  is  soluble  in  water.  This  is  most  conveniently  done  by  ig- 
niting and  weighing  the  insoluble  matter  and  deducting  the  weigh- 
found  from  that  of  the  total  ash  previously  determined.  The  aqueous 
solution  can  then  be  used  for  the  determination  of  the  chlorides,  alka- 
linity and  other  data.  Some  analysts  apply  the  term  " soluble  ash" 
to  the  ash  left  on  igniting  the  residue  obtained  by  evaporating  to  dryness 
the  filtered  aqueous  solution  of  the  substance.  This  is  not  identical 
with  the  soluble  portion  of  the  ash  of  the  whole  substance,  and  should 
be  called  in  preference  the  "ash  of  the  aqueous  extract." 

The  alkalinity,  or  capacity  of  the  ash  for  neutralising  acid,  is  a  useful 
indication.  It  is  commonly  expressed  in  terms  of  K2O,  and  is  estimated 
by  titrating  the  filtered  aqueous  solution  of  the  ash  with  standard  acid. 

Poisonous  metals  are  apt  to  occur  as  impurities  in  certain  commer- 
cial organic  products,  being  accidentally  introduced  during  the  process 
of  preparation.  The  objectionable  metals  most  commonly  occurring 
are  arsenic,  lead,  copper,  zinc  and  tin,  and  in  ordinary  cases  the  search 
may  be  limited  to  these. 

Liquids. — In  some  cases,  as,  for  instance,  vinegar  and  lemonade, 
the  metallic  impurities  may  be  sought  for  in  the  original  liquid,  but  in 
others  it  is  desirable  to  evaporate  the  liquid  carefully  to  dryness,  ignite 
the  residue,  and  test  the  resultant  ash.  The  evaporation  should  be 


ASH. 


75 


conducted  in  porcelain.  One  hundred  c.c.  of  such  liquids  as  beer, 
cider  or  vinegar  will  usually  suffice  for  the  examination,  but  sometimes 
the  use  of  considerably  larger  volumes  is  desirable.  Towards  the  end 
of  the  evaporation,  an  addition  of  strong  nitric  and  sulphuric  acids 
should  be  made,  the  quantity  used  depending  on  the  amount  of  organic 
matter  to  be  destroyed.  The  evaporation  is  then  carefully  completed 
and  the  residue  ignited  at  a  low  red  heat.  After  cooling,  the  ash  is 
moistened  with  nitric  acid  and  i  drop  of  sulphuric  acid,  and  again 
ignited.  It  is  then  again  treated  with  a  few  drops  of  nitric  acid, 
which  is  evaporated  off  cautiously,  the  process  being  stopped  directly 
acid  fumes  cease  to  be  copiously  evolved.  The  residue  is  then  treated 
with  hot  water,  and  the  solution  filtered,  when  the  following  scheme 
of  analysis  should  be  followed. 


Aqueous  Solution  may  contain  copper,  zinc, 
iron.      Add  excess  of  ammonia  and  filter 

Residue  may  contain  lead,  tin.      Wash,  and 
pour  boiling  solution  of  ammonium  acetate 
on  the  filter 

Precipitate 

may  contain 
iron,     phos- 
phates. 

Filtrate,  if  bit 
per.   Divide  ii 

i  .    A  ci  d  i  f  y 
with    acetic 
acid  and  add 
potassium 
ferrocyanide 
Bro  wni  sh 
precipitate 
or  colou  r  a  - 
tion  is  indic- 
ative of  cop- 
per. 

le,  contains  cop- 
vto  two  portions. 

2.  Heat  to  boil-  1 
ing,   and    add  ! 
p  otassiu  m 
ferrocyanide.    : 
White    pre- 
cipitate or 
turbidity    i  n- 
dicates  zinc. 

Solution 

Acidify    with 
acetic  acid,  and 
add     potassium 
chromate.   A 
chrome     yellow 
precipitate    i  n- 
dicates  lead. 

Residue.     Ignite  filter 
paper,  fuse  ash  in  porce- 
lain crucible  with  potas- 
sium cyanide,   dissolve 
product,  in  water,  filter, 
boil  insoluble  residue 
with  strong  hydrochlor- 
ic acid  ;  dilute,  and  treat 
clear  solution  with  mer- 
curic chloride.    A  white 
silky  precipitate  of  mer- 
curous  chloride  is  due 
to  tin. 

Minute  traces  of  copper  are  perhaps  best  detected  by  introducing  a 
knitting  needle  into  the  slightly  acidified  and  tolerably  concentrated 
aqueous  solution  of  the  ash,  removing  it  after  it  some  hours,  cautiously 
rinsing  it  in  water,  and  then  immersing  it  in  dilute  ammonia,  with  free 
contact  of  air.  The  copper  precipitated  on  the  iron  will  pass  into 
solution,  and  may  be  detected  by  acidifying  the  ammoniacal  liquid 
with  acetic  acid  and  adding  potassium  ferrocyanide,  when  a  purple  or 
brownish  colouration  will  be  produced  if  a  trace  of  copper  be  present. 

Solids  may  be  examined  for  traces  of  the  foregoing  poisonous 
metals  in  precisely  the  same  way  as  liquids  which  have  been  concen- 
trated to  a  small  bulk  by  evaporation. 

The  detection  of  zinc  and  copper  in  food  articles  has  become  of  con- 
siderable importance  lately,  in  view  of  the  use  of  colouring  matters  con- 
taining these  substances,  and  the  tendency  to  restrictive  legislation  con- 


76  INTRODUCTION. 

earning  such  use.  Much  attention,  for  example,  has  been  given  to  the 
detection  of  zinc  in  dried  apples,  in  consequence  of  the  efforts  of  the 
German  government  to  prohibit  the  importation  of  American  dried 
apples,  under  the  allegati  on  that  they  were  dangerously  contaminated 
with  zinc  derived  from  the  plates  on  which  the  drying  is  conducted. 
Wiley,  in  a  bulletin  published  by  the  United  States  Department  of 
Agriculture,  has  given  the  results  of  an  investigation  into  this  question; 
in  some  cases  he  obtained  results  differing  materially  from  those 
obtained  upon  the  same  samples  by  the  German  chemists. 

In  most  cases,  especially  in  examining  food  and  household  articles, 
an  amount  of  arsenic  sufficient  to  be  of  sanitary  significance  may  be 
detected  by  Reinsch's  test,  using  a  liberal  allowance  of  hydrochloric 
acid,  since  the  more  highly  oxidised  forms  of  arsenic  (arsenates)  do 
not  give  the  reaction  in  the  presence  of  small  amounts  of  hydrochloric 
acid.  Reinsch's  test  cannot  be  applied  in  the  presence  of  active  oxid- 
ising agents,  such  as  chromates,  chlorates  or  nitrates.  Processes  for 
examination  of  beer,  glucose  and  foods  for  arsenic  will  be  described 
in  the  sections  devoted  to  such  substances. 

The  examination  for  arsenic  and  poisonous  metals  in  cases  of  sus- 
pected poisoning  does  not  come  within  the  scope  of  this  work  and  will 
not  be  described. 

The  detection  of  alum  and  other  mineral  adulterants  of  flour  and 
bread  is  described  under  "cereals." 

BEHAVIOUR  OF  ORGANIC  SUBSTANCES  WITH 
SOLVENTS. 

In  the  proximate  analysis  of  plants  and  other  complex  substances 
of  organic  origin,  a  systematic  treatment  with  solvents  is  a  most  valu- 
able means  of  separating  different  classes  of  compounds  from  each 
other*  The  systematic  use  of  solvents  has  been  worked  out  very 
thoroughly  by  Dragendorff  and  others,  whose  methods  will  be  described 
in  greater  detail  in  future  sections.  In  proximate  organic  analysis 
only  a  limited  use  is  made  of  the  stronger  acids  so  largely  employed 
injmineral  analysis,  while  the  use  of  alcohol,  ether,  chloroform  and 
other  organic  solvents  is  greatly  extended. 

Exhaustion  of  Organised  Tissues  by  Solvents. — In  assay- 
ing commercial  organic  substances  it  is  often  requisite  to  effect  as 
perfect  an  exhaustion  as  possible  of  an  organised  tissue  of  some  active 


ACTION    OF    SOLVENTS. 


77 


principle  or  valuable  constituent  existent  therein.  This  is  the  case  in 
the  assay  of  cinchona  barks  for  alkaloid,  of  seeds  and  oil-cakes  for  oil, 
and  of  sugar-cane  and  beet-root  for  sugar.  In  such  cases  the  cells 
which  contain  the  principles  to  be  extracted  are  only  incompletely 
ruptured  by  the  most  careful  pounding  or  crushing  of  the  sample,  and 
hence  solvents  can  only  act  on  the  contents  through  the  cell  walls,  and 
the  resultant  solution  can  only  pass  through  the  cell  walls  by  diffusion. 
This  often  renders  the  process  of  exhausting  organised  tissues  very 
tedious,  while  the  difficulty  is  enhanced  by  the  fact  that  economy  and 
convenience  of  subsequent  treatment  often  render  it  desirable  or  nec- 
essary to  use  a  very  limited  quantity  of  solvent.  Under  these  cir- 
cumstances, an  apparatus  which  will  act  almost  automatically  and 
allow  of  complete  exhaustion  by  a  small  quantity  of  solvent 
possesses  great  advantages. 

Soxhlet's  Tube. — For  the  automatic  exhaustion  of  a 
substance  by  a  volatile  solvent,  no  better  arrangement  has 
been  described  than  an  ingenious  device  of  Szombathy, 
commonly  called  Soxhlet's  apparatus  (Fig.  46).  The  sub- 
stance to  be  extracted  is  inclosed  in  a  plaited  filter  or 
cylinder  of  filter-paper,  or  if  it  be  coarse  it  is  sufficient 
simply  to  place  it  loose  in  a  large  test-tube,  having  an 
aperture  at  the  bottom  closed  by  a  plug  of  glass-wool. 
Thus  arranged,  the  tube  or  filter  with  its  contents  is  placed 
in  a  Soxhlet  tube,  having  a  little  glass-wool  at  the  bottom, 
and  adapted  by  means  of  a  cork  to  a  flask  containing  the 
solvent.  A  vertical  condenser  is  adapted  to  the  upper  end 
of  the  Soxhlet's  tube,  and  the  solvent  kept  boiling  by  a 
suitable  source  of  heat.  In  the  case  of  petroleum  spirit, 
ether  or  other  volatile  and  inflammable  solvent,  this  should 
be  a  water-bath  kept  hot  by  a  small  flame  or  an  electric 
stove.  As  the  solvent  boils  it  is  condensed  and  falls  on 
the  substance  to  be  extracted,  remaining  in  contact  with 
it  until  both  the  inner  and  outer  tubes  are  filled  to  the  level  of  the 
syphon,  when  the  solution  passes  off  into  the  flask,  to  be  redistilled 
and  recondensed,  and  so  on  until  the  process  is  judged  to  be  complete. 
With  a  proper  arrangement  of  the  source  of  heat,  the  extraction  goes 
on  regularly  and  automatically.  On  changing  the  flask  and  replacing 
the  inner  tube  by  one  containing  a  fresh  sample,  the  apparatus  is 
ready  to  be  used  for  another  extraction. 


FIG.  46. 


78  INTRODUCTION. 

The  paper  thimbles  made  by  Schleicher  and  Schiill  are  convenient 
for  use  with  extraction  apparatus. 

A  very  simple  and  convenient  form  of  exhauster,  adapted  either  for 
extraction  or  repercolation,  has  been  described  by  Dunstan  and  Short 
(Pharm.  Jour.,  1882-3,  [3],  13,  664).  It  consists  of  two  glass  tubes,  the 
wider  of  which  is  drawn  out  at  one  end.  The  narrower  and  somewhat 
shorter  tube  fits  into  the  outer  one  with  much  margin,  and  is  also  drawn 
out  in  such  a  way  as  to  allow  the  end  to  protrude  from  the  drawn-out 
end  of  the  wider  tube  when  the  smaller  is  inserted  therein.  At  the 
point  where  the  outer  tube  commences  to  contract  it  is  indented  on 
opposite  sides,  by  which  means  two  ledges  are  formed  within  the  tube 
which  serve  as  supports  for  the  narrower  tube.1  The  inner  tube  serves 
to  contain  the  substance  to  be  exhausted.  The  lower  drawn-out  end 
of  the  wider  tube  is  fitted  by  a  cork  to  the  flask  containing  the 
volatile  solvent,  while  the  upper  end  is  connected  with  a  condensing 
arrangement. 

J.  West-Knights  has  described  a  form  of  exhauster  which  may  be 
conveniently  used  when  the  quantity  of  material  to  be  extracted  is  some- 
what small  (Analyst,  1883,  8,  65).  A  percolator  is  made  by  cutting 
off  the  bottom  from  a  test-tube  of  suitable  size,  and  blowing  a  hole  in 
the  side  of  the  tube  about  an  inch  from  the  top.  A  disc  of  filter-paper 
or  fine  cambric  is  tied  over  the  lower  end  of  the  tube.  The  substance 
to  be  extracted  is  placed  in  the  tube,  and  kept  in  its  place  by  some  glass- 
wool  and  a  perforated  disc  of  metal,  and  the  tube  with  its  contents 
then  fixed  by  a  cork  to  the  lower  end  of  the  tube  of  a  vertical  condenser. 
This  is  adapted  by  a  larger  cork  to  the  neck  of  an  ordinary  flask  con- 
taining the  volatile  solvent,  on  heating  which  the  vapour  passes  through 
the  hole  in  the  side  of  the  test-tube  up  into  the  tube  of  the  condenser, 
where  it  is  liquefied.  The  condensed  liquid  drops  right  into  the  test- 
tube,  percolates  through  the  substance  to  be  extracted,  and  falls  to  the 
bottom  of  the  flask,  to  be  again  volatilised.  As  the  percolator  is  inside 
the  flask,  its  contents  are  kept  constantly  at  the  b.  p.  of  the  solvent,  and, 
the  action  being  continuous  and  automatic,  very  rapid  exhaustion 
may  be  effected. 

The  "flow"  extractor  devised  by  Burgess  and  shown  in  the  sketches 
in  Figs.  47  to  49  (apparatus  made  by  Miiller,  Orme  and  Co.,  London) 
is  more  effective  than  the  Soxhlet  for  many  purposes,  the  substance 

^he  indentations  are  made  by  gently  pressing  each  side  of  the'tube  when  red-hot  with  a 
pair  of  crucible  tongs. 


ACTION    OF    SOLVENTS. 


79 


being  kept  covered  with  the  solvent  in  use  and  a  flow  of  clean  solvent 
continuously  passing  through  it.     The  joints  are  ground-in  joints. 

Other  forms  of  exhauster  have  been  contrived  by  Church,  Drechsel 
Angell,  Thorns,  Thresh  (Pharm.  Jour.,  1884-5,  [3],  J5,  281)  and  others, 
but  those  described  will  be  found  sufficient  for  most  purposes. 

Employment    of    Immiscible    Solvents.— In    mineral    analysis 
this  method  finds  but  few  applications,  but  in  proximate  organic  anal- 


FIG.  47- 


FIG.  48. 


FIG.  49. 


ysis  one  of  the  most  valuable  means  of  effecting  separations  con- 
sists in  agitating  the  solution  of  a  substance  in  one  solvent,  with  another 
solvent  insoluble  or  only  slightly  soluble  in  the  former  liquid.  Under 
these  circumstances,  the  dissolved  body  is  distributed  between  the  two 
solvents  in  proportions  which  are  dependent  on  the  relative  solubility 
of  the  substance  in  the  two  media,  and  the  relative  quantities  of  the 
two  media  employed.  Thus,  it  may  be  supposed  that,  if  a  substance 
be  99  times  more  soluble  in  chloroform  than  in  water,  and  its  aqueous 
solution  be  shaken  with  an  equal  measure  of  chloroform,  99%  of  the 
whole  substance  will  pass  into  the  chloroform.  On  separating  this 
layer,  and  again  agitating  the  residual  aqueous  liquid  with  an  equal 


8o 


INTRODUCTION. 


quantity  of  chloroform,  QQ%  of  the  remaining  substance  will  be  dis- 
solved, thus  making  the  exhaustion  practically  complete.  The  dis- 
tribution of  a  solid  between  two  non-miscible  solvents  is  dealt  with 
in  works  on  Physical  Chemistry,  for  example,  Nernst's  "Theoretische 
Chemie." 

In  making  a  proximate  analysis  by  means  of  immiscible  solvents, 
much  of  the  success  in  practice  depends  on  the  care  and  skill  with  which 
the  manipulation  is  conducted.  The  most  convenient  apparatus  for 
effecting  the  treatment  consists  of  a  pear-shaped  (Fig. 
50)  or  cylindrical  glass  separator,  furnished  with  a  tap 
below  and  a  stopper  at  the  top.  The  tube  below  the 
tap  should  be  ground  obliquely  so  as  to  prevent  loss  of 
liquid  by  imperfect  delivery.  Supposing  that  it  be 
desired  to  effect  the  separation  of  a  substance  from  an 
aqueous  liquid  by  agitation  with  ether,  the  former  is 
introduced  into  the  separator,  of  which  it  should' not 
occupy  more  than  one-third,  acid  or  alkali  added  as  may 
be  desired,  and  next  a  volume  of  ether  about  equal  to 
that  of  the  aqueous  liquid.  The  stopper  is  then  inserted 
and  the  whole  thoroughly  shaken  together  for  a  minute 
or  two,  and  then  set  aside.  As  a  rule,  the  contents  will 
readily  separate  into  two  well-defined  layers,  the  lower 
of  which  is  aqueous  and  the  upper  ethereal.  Some- 
times separation  into  layers  does  not  occur  readily,  the 
liquid  remaining  apparently  homogeneous,  forming  an  emulsion  or 
assuming  a  gelatinous  consistency.  In  such  cases  separation  may 
sometimes  be  induced  by  thoroughly  cooling  the  contents  of  the  sepa- 
rator. In  the  case  of  ether,  the  separation  may  always  be  effected 
by  adding  an  additional  quantity  of  ether  and  reagitating,  or,  when 
the  employment  of  a  sufficient  excess  of  ether  is  inconvenient  or 
impracticable,  the  addition  of  a  few  drops  of  alcohol,  followed  by  a 
gentle  rotatory  motion  of  the  liquid,  will  almost  invariably  cause 
separation  to  occur  promptly. 

Separation  having  taken  place,  the  aqueous  layer  should  be  run  off 
by  the  tap  into  another  separator,  where  it  can  again  be  agitated  with 
ether  to  insure  the  complete  removal  of  the  substance  to  be  dissolved 
therein.  The  ethereal  liquid  remaining  in  the  first  separator  should 
be  shaken  with  a  fresh  quantity  of  alkaline  or  acidified  water,  which 
is  then  tapped  off  as  before,  and  the  remaining  traces  removed  by 


FIG.  50. 


ACTION    OF    SOLVENTS.  8 1 

treating  the  ether  with  a  little  pure  water.  This  having  in  turn  been 
run  off  to  the  last  drop,  the  ethereal  solution  can  next  be  removed  by 
the  tap,  but  a  preferable  plan  is  to  pour  it  out  of  the  top  of  the  sepa- 
rator, by  which  means  any  contamination  by  the  traces  of  water  ad- 
hering to  the  sides  of  the  glass  will  be  avoided. 

When  amyl  alcohol,  benzene,  or  petroleum  ether  is  employed,  the 
manipulation  is  the  same  as  that  just  described;  but  when  chloroform 
is  used  or  a  mixture  containing  a  considerable  proportion  of  that  sol- 
vent, the  aqueous  liquid  forms  the  upper  stratum,  and  the  chloroform 
solution  can  at  once  be  removed  by  the  tap. 

The  tendency  to  form  an  obstinate  emulsion  is  greater  when  the 
aqueous  liquid  is  alkaline,  and  is  often  very  troublesome  when  chloro- 
form, benzene,  or  petroleum  spirit  is  substituted  for  ether.  In  such 
cases  the  employment  of  a  larger  quantity  of  the  solvent  sometimes 
causes  separation,  but,  when  admissible,  a  better  plan  is  the  addition 
of  ether.  This  answers  very  successfully  for  the  isolation  of  strych- 
nine, which  is  nearly  insoluble  in  unmixed  ether,  but  readily  soluble 
in  a  mixture  of  equal  measures  of  ether  and  chloroform.  This 
solvent  is  heavier  than  water  and  is  capable  of  very  extensive 
application. 

It  is  evident  that  the  treatment  can  be  repeated  any  number  of  times 
requisite  to  ensure  the  complete  extraction  of  substances  having  a 
limited  solubility  in  the  solvents  employed,  and  these  can  themselves 
be  varied  in  a  systematic  manner,  as  is  done  in  Dragendorff's  method 
for  the  separation  of  alkaloids  and  other  active  principles. 

The  separation  of  immiscible  solvents  is  in  many  cases  promoted  by 
rapid  rotation.  The  centrifugal  machines  employed  for  the  rapid  anal- 
ysis of  milk  do  not  usually  give  sufficient  speed  for  this  purpose,  but 
some  of  the  smaller  forms  intended  for  clinical  work  can  be  operated 
at  very  high  velocity,  and  by  their  use  a  small  amount  of  such  mixtures 
can  often  be  separated  rapidly  and  thoroughly. 

Care  must  be  taken  to  ascertain  the  purity  of  the  solvents  used  in 
these  methods,  especially  when  toxicological  investigations  are  being 
conducted.  Vaughan  has  reported  a  case  in  which  a  sample  of  ether 
made  by  a  prominent  house  contained  a  poisonous  substance  in  such 
amount  that  the  residue  left  by  the  evaporation  of  50  c.c.  of  the  ether 
killed  a  guinea-pig  in  a  short  time.  Chloroform  often  contains  cor- 
bonyl  chloride,  in  which  case  it  is  also  acid  owing  to  the  presence  of 
hydrogen  chloride. 
Vol.  I.— 6 


82 


INTRODUCTION. 


Fig.  51  shows  a  special  apparatus  for  use  with  solvents  lighter  than 
water. 

The  cylinder  A  should  hold  about  1000  c.c.  Two  openings  are  not 
necessary,  since  both  tubes  may  pass  through  the  cork,  but  the  arrange- 
ment shown  is  more  convenient.  600  c.c.  of  the  solution  are  placed 
in  the  cylinder,  300  c.c.  of  solvent  added  and  the  mixtures  well 

shaken.  The  rest  of  apparatus  is  then 
attached.  The  flask  B  has  a  capacity  of 
200  to  300  c.c.;  the  solvent  in  it  is  heated  by 
a  water-bath.  The  vapour  passes  by  a  into 
b,  the  condensed  liquid  flows  to  the  bottom 
of  A  and  rises  through  the  solution;  the 
upper  layer  returns  through  c  into  B.  The 
tube  c  should  not  extend  into  the  liquid  in  B. 
A  small  quantity  of  aqueous  liquid  may 
collect  at  intervals  in  B  and  should  be 
removed. 

The  table  on  page  83  shows  the  behaviour 
of  the  principal  organic  substances  on  treat- 
ment with  water,  made  slightly  acid  or 
alkaline,  and  solvents  immiscible  therewith, 
such  as  ether,  chloroform,  amyl  alcohol, 
benzene,  and  petroleum  ether.  It  must  not, 
however,  be  supposed  that  the  immiscible 
solvents  can  be  employed  indifferently,  as 
some  of  the  substances  are  removed  from 
their  aqueous  solutions  by  one  solvent,  but 

are  unaffected  by  others  owing  to  their  limited  solubility  therein. 
This  is  especially  the  case  with  the  alkaloids  and  glucosides,  and  hence 
the  table  must  merely  be  regarded  as  showing  the  general  tendency, 
their  behaviour  when  treated  with  the  individual  solvents  being 
deferred  for  full  description  later. 


ACTION    OF    SOLVENTS. 


83 


i  s 

Z       ^3 
W       u 

S  vS 
S  S  .. 
g  II 

I  H 

I  li 
s  63 
i^ 


S.a 


HH          >    w 

*    1.S 

^    3§ 
%     ~~° 

IS 

£9   ^^ 


i|i 

p<  -at 


o    *^  w 

'^   C 

p^          N 

O    . 

1 11 

S  li 

gll 

H    'i  jf 

O     8  § 
2    I? 

S    ^^ 
2    2« 

S  Jg 

w    M 

K-l  C 

pa    'B 
<    .§ 

H       be 

• 

O 


sis 

s  "-C 


a«2     S"M  'S'C 

0.3  e     «S  8 

^S    |£  £    8-| 
Illlll^t 


ic 
in 


{Ii!if0]|IJ!iiiJL 


> 

**•» 

0(0 


g 
ill 


ALCOHOLS. 

BY  G.  C.  JONES,  F.I.C.     CONSULTING  CHEMIST. 

The  term  "  alcohol "  when  used  without  qualification  and  as  a  proper 
name  is  generally,  and  throughout  this  book  always,  to  be  understood 
as  applying  to  ethyl  alcohol. 

This  section  will  deal  only  with  those  monohydric  aliphatic  alcohols 
which  are  either  themselves  of  commercial  importance  or  which  are 
essential  constituents  or  commonly  occurring  impurities  of  other 
articles  of  commerce. 

A  slight  difficulty  in  the  arrangement  of  the  matter  of  the  section 
exists.  In  that  part  which  deals  with  beer  and  wines  the  difficulty 
does  not  arise;  clearly  that  part  must  deal  with  the  analysis  of  beer 
and  wines  and  the  estimation  in  them  of  alcohol  and  other  chemical 
entities.  Ethyl  and  methyl  alcohols  are  incapable  of  analysis  in  the 
commercial  sense,  and  perhaps  the  analysis  of  commercial  alcohol 
and  wood  spirit  should  have  been  relegated  to  that  part  of  the  section 
which  deals  with  "spirits,"  as  their  analysis  is  largely  a  matter  of  esti- 
mating the  amount  of  their  impurities.  Such  an  arrangement  would 
have  left  under  the  chief  headings  only  methods  for  the  detection  and 
estimation  of  ethyl  and  methyl  alcohols  in  liquids  of  which  they  are 
not  principal  constituents.  In  the  circumstances  it  has  been  decided 
to  retain  the  arrangement  of  the  third  edition  of  this  work  as  far  as 
possible,  owing  to  the  fact  that  many  analysts  are  acquainted  with  that 
arrangement.  For  the  convenience  of  others  the  various  subsections 
and  parts  of  these  will  be  somewhat  more  clearly  indicated  than  in  the 
third  edition  of  this  work. 

METHYL  ALCOHOL. 

Carbinol,  Purified  Wood  Spirit,  CH3.OH. 

The  chief  source  of  methyl  alcohol  is  the  aqueous  portion  of  the 
distillate  which  results  from  the  dry  distillation  of  wood,  but  con- 
siderable quantities  are  now  obtained  from  vinasse,  the  residue 
remaining  after  the  distillation  of  beet  molasses. 

Pure  methyl  alcohol  is  a  colourless,  mobile  liquid  with  only  a  very 

85 


86 


ALCOHOLS. 


faint  pleasant  odour.  Its  b.  p.,  according  to  Fuchs,  ranges  from 
65.06°  at  710  mm.  to  68.00°  at  790  mm.,  and  can  be  calculated  for  any 
intermediate  pressure  from  these  numbers  (Zeits.  angew.  Chem.,  1898, 
38,  871).  The  b.  p.  maybe  used  as  a  test  of  reputed  100%  methyl 
alcohol.  The  low  number  given  by  some  workers,  who  were  at 
great  pains  to  dehydrate  the  spirit,  is  no  doubt  due  to  acetone  which 
depresses  it  notably,  a  minimum  being  reached  when  the  acetone 
amounts  to  10%  (Petitt,  /.  Physical  Chem.,  1899,  3,  349).  The 
melting-point,  according  to  Ladenburg  and  Krugel,  is  — 94.9°  (Ber., 
1899,  32,  1821).  The  sp.  gr.  at  i5°/i5°  is,  according  to  Klason 
and  Norlin,  0.796472  (Arkiv  Kem.  Min.  GeoL,  1906,  2,  No.  24,  6). 
These  authors  have  recalculated  the  met,hyl  alcohol  tables  of 
Dittmar  and  Fawsitt  (Trans.  Roy.  Soc.  Edin.  1889,  33,  ii,  509),  and 
their  results  occupy  26  pages  in  the  Arkiv  Kem.  Min.  GeoL,  1907,  2, 
No.  27.  The  reviser  of  this  section  has  had  frequent  occasion  to  use 
a  methyl  alcohol  table  and  has  found  abundant  proof  that  the  course 
commonly  recommended,  namely  to  break  down  to  one-third  strength 
and  use  the  ethyl  alcohol  tables,  may  lead  to  serious  errors.  At 
46.4%  by  weight  the  numbers  in  the  tables  are  identical,  but  at  25 
per  cent,  strength  the  error  introduced  by  using  the  ethyl  alcohol 
table  for  estimating  methyl  alcohol  is  more  than  9%.  An  abridge- 
ment of  Klason  and  Norlin's  table  follows. 


Specific 
Gravity 
i5°/i5° 

Methyl  Alco-  ! 
hoi,  per  cent, 
by  weight. 

Specific 
Gravity 
i5°A5° 

Methyl  Alco- 
hol, per  cent, 
by  weight. 

Specific 
Gravity 

i$°As° 

Methyl  Alco- 
hol, per  cent, 
by  weight. 

0.7965 

100.00 

0.814 

93-74 

0.832 

87.24 

0.797 

99.82 

Si              -39 

3 

86.88 

8 

•47 

6 

•°3 

4 

•52 

9 

.11 

7 

92.68 

5 

.16 

0.800 

98.75 

8 

•32 

6 

85-79 

i 

•39 

9 

91.96 

7 

•  42 

2 

•°3 

0.820 

.60 

8 

.04 

3 

97.67 

i 

.24 

9 

84.67 

4 

-3i 

2 

90.88 

0.840 

.29 

5 

96.96 

3 

•52 

i 

83.91 

6 

.60 

4 

.16 

2 

•53 

7 

•25 

5 

89.80 

3 

•*5 

8 

95.89 

6 

•43 

4 

82.77 

9 

•54 

7 

.07 

5 

•39 

0.810 

.18 

8 

88.70 

6 

.01 

i 

94.82 

9 

•34  . 

7 

81.63 

2 

.46 

0.830 

87.97 

8 

•25 

3 

.10 

i 

.61 

9 

80.86 

METHYL   ALCOHOL. 


Specific 
Gravity 

Methyl  Alco- 
hol, per  cent, 
by  weight. 

Specific 
Gravity 

Methyl  Alco- 
hol, per  cent, 
by  weight. 

Specific 
Gravity 

Methyl  Alco- 
hol, per  cent, 
by  weight. 

0.850 

80.47 

0.901 

58.90 

0.952 

31.69 

i 

.08 

2 

•43 

3 

.07 

2 

79.69 

3 

57-96 

4 

3°-44 

3 

•3° 

4 

-49 

5 

29.79 

4 

78.91 

5 

.01 

6 

•15 

•51 

6 

56.53 

7- 

28.48 

6 

.11 

/ 

.06 

8 

27.80 

7 

77.71 

8 

55.58 

9 

.12 

8 

•3° 

9 

.11 

0.960 

26.44 

9 

76.90 

0.910 

54-64 

i 

25-73 

0.860 

•5° 

i 

.18 

2 

.02 

i 

.10 

2 

53.72 

3 

24-  31 

2 

3 

75-7° 
•3° 

3 
4     . 

.25 
52.79 

4 

5 

23.59 

22.89 

4 

74.89 

5 

•31 

6 

.19 

5 

.49 

6 

51  .83 

7 

21.49 

6 

.09 

7 

•34 

8 

20.79 

7 

8 

50-85 

9 

.09 

8 

•29 

9 

•35 

0.970 

19.38 

9 

72.89 

0.920 

49.84 

i 

18.68 

0.870 

.48 

i 

•33 

2 

17.98 

i 

.07 

2 

48.81 

3 

.28 

2 

7I-65 

3 

.28 

4 

16.58 

3 

•23 

4 

47-74 

5 

15.85 

4 

70.81 

r 

.20 

6 

.12 

5 

-38 

6 

46.66 

7 

14.40 

6 

69-95 

7 

.12 

8 

13.67 

7 

•53 

8 

45-57 

9 

12.97 

8 

.10 

9 

•03 

0.980 

.27 

9 

68.68 

0.930 

44.49 

i 

0.880 

•25 

i 

43-96 

2 

10-94 

i 

67.83 

2 

•  42 

3 

.26 

2 

.40 

3 

42.88 

4 

9.58 

3 

66.97 

4 

•34 

5 

8-94 

4 

•53 

5 

41.79 

6 

•29 

5 

.09 

6 

'•23 

7 

7.64 

6 

65-65 

7 

40.68 

8 

6-99 

7 

.20 

8 

.12 

9 

.36 

8 

64.75 

9 

39.56 

0.990 

5-72 

9 

•31 

0.940 

.00 

i 

.10 

0.890 

63.86 

i 

38.42 

2 

4-47 

i 

.42 

2 

37-84 

3 

3.89 

2 

62.98 

3 

.24 

4 

•30 

3 

•54 

4 

36.64 

5 

2.72 

4 

5 

.09 

61.65 

1 

•03 

35-42 

6 

.14 
1.62 

6 

.20 

7 

34.81 

8 

.10 

7 

60.75 

8 

.20 

9 

o-55 

8 

•29 

9 

33-58 

T  .OOO 

o.oo 

9 

59-83 

0.950 

32.95 

0.900 

.36 

1 

•32 

88  ALCOHOLS. 

Methyl  alcohol  containing  only  a  small  amount  of  water  and  a 
slight  trace  of  acetone  is  now  largely  sold  in  the  United  States,  usually 
under  proprietary  names,  such  as  "  Columbian  Spirit,"  "  Colonial 
Spirit,"  "  Kahol."  It  has  been  much  used  as  a  substitute  and  adul- 
terant for  ethyl  alcohol,  especially  in  tinctures  and  varnishes. 

Detection  of  Methyl  Alcohol. — Only  those  tests  which  distinguish 
sharply  between  methyl  and  ethyl  alcohols  are  of  practical  importance 
and  only  such  will  be  dealt  with  here.  The  quickest  and  most  satis- 
factory are  those  which  depend  on  the  oxidation  of  the  methyl  alcohol 
to  formaldehyde  by  means  of  a  heated  copper  wire,  and  the  identi- 
fication of  the  formaldehyde  by  a  colour  reaction  with  resorcinol. 
There  are  several  modifications  of  this  test,  some  quicker  and  less 
sensitive,  others  requiring  rather  more  time  but  capable  of  detecting 
smaller  amounts  of  methyl  alcohol. 

Mulliken-Scudder  Test  (Amer.  Chem.  /.,  1899,  21,  266).— A 
copper-wire  spiral  is  heated  to  redness  and  plunged  into  3  c.c.  of  the 
liquid  to  be  tested  or,  if  the  latter  is  a  strong  spirit,  into  3  c.c. 
of  a  solution  diluted  so  as  to  contain  not  more  than  20%  total 
alcohols.  The  treatment  with  hot  oxidised  copper  wire  is  repeated 
three  or  four  times.  One  drop  of  0.5%  aqueous  solution  of  resor- 
cinol is  added,  and  the  mixture  poured  cautiously  down  the  side 
of  a  test-tube  containing  a  little  concentrated  sulphuric  acid.  A  rose- 
red  contact  ring,  and  on  gentle  shaking  red  flocks,  will  appear  if  the 
original  liquid  contained  much  methyl  alcohol.  The  test  can  be 
carried  out  in  five  minutes  and  shows  8  to  10%  of  methyl  alcohol 
in  ethyl  alcohol.  More  sensitive  reagents  for  formaldehyde  exist, 
for  example  gallic  acid,  but  its  use  is  not  permissible  as  ethyl  alcohol 
itself,  when  oxidised  by  a  copper  spiral,  gives  enough  formaldehyde 
to  show  the  gallic  acid  reaction. 

United  States  Pharmacopoeia  Test. — This  is  a  modification  of  the 
last,  occupying  about  fifteen  minutes  and  showing  2%  of  methyl 
alcohol  in  ethyl  alcohol.  The  liquid  is  diluted  so  as  to  contain 
about  10%  total  alcohols,  and  placed  in  a  test-tube  surrounded 
by  cold  water.  It  is  oxidised  by  five  or  six  applications  of  the  hot 
copper  spiral,  after  which  it  is  filtered  and  boiled  till  free  from  any 
odour  of  acetaldehyde.  After  cooling,  addition  of  one  drop  of  0.5  per 
cent,  resorcinol  solution  and  pouring  on  to  sulphuric  acid,  it  is  allowed 
to  stand  three  minutes,  after  the  end  of  which  time  it  is  gently  rotated. 
If  no  rose-red  ring  appears,  less  than  2  per  cent,  of  methyl  alcohol  is 


fi    UNIVER 
V 

^£*tL: 

METHYL   ALCOHOL.  89 

present.  Acetaldehyde  gives  with  resorcinol  a  yellowish-brown  ring 
and  flocks,  hence  the  advantage  of  expelling  it  from  the  solution.  It 
need  scarcely  be  pointed  out  that  the  red  ring  and  flocks  are  given  by 
all  substances  which  yield  formaldehyde  on  oxidation,  but  added 
methyl  alcohol  is  the  only  such  substance  likely  to  be  present  in 
quantity  in  commercial  spirits  or  tinctures. 

Test  for  Quantities  Under  2  Per  Cent. — The  liquid  (50  c.c.)  is 
three  times  fractionated  through  a  rod-and-disc  or  "pear"  still-head, 
and  the  final  first  fraction  diluted  and  submitted  to  the  United  States 
Pharmacopoeia  test.  With  strong  spirit,  successive  first  fractions  of 
35  and  20  c.c.  may  be  collected  and  redistil  ed,  and  the  first  i  c.c.  of 
the  third  distillation  taken  for  the  test.  If  the  liquid  to  be  examined 
is  only  weakly  alcohol'c,  a  vinegar  for  instance,  successive  first  frac- 
tions of  20  and  10  c.c.  may  be  collected  and  the  first  3  c.c.  of  the  third 
distillation  taken  for  the  test.  As  small  an  amount  as  0.1%  of 
methyl  alcohol  may  be  detected  in  this  way. 

The  Sangle"-Ferriere-Cuniasse  Test  (Ann.  Chim.  anal.,  1903,  8, 
82),  which  depends  on  oxidation  by  permanganate  and  the  use  of 
phloroglucinol  as  reagent,  is  slow,  but  a  quicker  modification  by  Scud- 
der  and  Biggs  is  worth  description,  because  when  permanganate  is 
used  as  oxidising  agent  less  acetaldehyde  seems  to  be  formed  than  when 
hot  copper  is  used.  Scudder  and  Biggs  (/.  Amer.  Chem.Soc.,  1906, 
28,  1202)  recommend  that  to  10  c.c.  of  the  solution  to  be  tested,  0.5  c.c. 
of  concentrated  sulphuric  acid  and  5  c.c.  of  a  saturated  solution  of 
potassium  permanganate  be  added.  The  temperature  should  be 
between  20°  and  25°:  below  18°  action  is  slow,  while  above  30°  for- 
maldehyde may  be  lost.  After  two  minutes,  the  solution  is  decolourised 
by  sulphurous  acid  and  boiled  till  it  no  longer  smells  either  of  this  or  of 
acetaldehyde.  It  is  then  tested  with  resorcinol.  It  is  important  not 
to  add  much  more  than  the  stated  quantity  of  sulphuric  acid,  and  a 
control  experiment  with  pure  ethyl  alcohol  is  advisable  to  those  who 
have  no  great  experience  of  the  test. 

Trillat  Test. — As  it  is  claimed  by  more  than  one  worker  that  this 
test  (Compt.  rend.,  1899,  127,  232)  is  capable  of  detecting  0.1% 
of  methyl  alcohol  in  ethyl  alcohol,  it  must  be  referred  to.  The  reviser 
of  this  section  would  not  venture  to  recommend  it  unless  several 
pages  could  be  spared  to  describe  the  difficulties  which  surround  it. 
Moreover,  it  occupies  five  hours,  in  which  time  the  amount  of  methyl 
alcohol  may  be  accurately  estimated  by  the  method  of  Thorpe  and 


90  ALCOHOLS. 

Holmes.  Those  who  have  time  to  acquire  skill  in  this  very  interesting 
but  difficult  test  are  referred  to  a  paper  by  Scudder  (/.  Amer.  Chem. 
Soc.,  1905,  27,  892)  which  reviews  all  the  principal  tests  which  had  been 
proposed  before  that  date  for  the  detection  of  methyl  alcohol. 

Voisenet  (Bull.  Soc.  chim.,  1906  [iii],  35, 748)  has  described  a  test 
which  is  stated  to  be  sufficiently  sensitive  to  detect  one  part  of  methyl 
alcohol  in  20,000  of  ethyl  alcohol.  As  the  method  is  based  on  the 
regulated  oxidation  of  the  sample  by  chromic  acid  mixture,  the  claim 
must  be  received  with  caution  as  ethyl  alcohol  itself  yields  appreciable 
traces  of  formaldehyde  when  oxidised  by  chromic  acid  mixture  even 
in  the  cold. 

Hinkel  (Analyst,  1908,33, 41 7)  has  investigated  severalof  the  methods 
which  depend  on  the  oxidation  of  methyl  alcohol  to  lormaldehyde  and 
the  detection  of  this  substance,  and  he  finds  morphine  hydrochloride  to 
be  the  most  delicate  reagent  (see  under  "  Formaldehyde  ")  for  the  latter 
purpose,  and  as  oxidising  agent  prefers  ammonium  persulphate,  which  is 
said  to  produce  but  little  formaldehyde  from  ethyl  alcohol.  To  i  c.c. 
of  the  spirit  suspected  to  contain  methyl  alcohol,  0.8  grm.  of  ammonium 
persulphate  and  3  c.c  of  dilute  sulphuric  acid  (1:5)  are  added  and  the 
mixture  diluted  with  water  to  20  c.c.  and  distilled.  The  distillate  is 
collected  in  test-tubes  in  five  separate  portions  of  2  c.c.  at  a  time. 
The  first  two  portions,  which  contain  all  the  acetaldehyde,  are  rejected 
and  each  of  the  remaining  portions  tested  as  follows:  To  each  por- 
tion a  few  drops  of  0.5%  solution  of  morphine  hydrochloride  are 
added  and  strong  sulphuric  acid  is  poured  into  each  test-tube  so  as 
to  form  a  layer  at  the  bottom.  In  the  presence  of  formaldehyde,  a 
violet  ring  is  formed  at  the  junction  of  the  liquids.  Acetaldehyde 
gives  an  orange  colour  with  the  reagent,  as  may  be  seen  by  testing 
the  first  portion  of  the  distillate.  The  reagent  is  capable  of  detecting 
one  part  of  formaldehyde  per  million  parts  of  water,  so  that  a  control 
experiment  with  pure  ethyl  alcohol  Is  absolutely  necessary,  since, 
even  when  ammonium  persulphate  is  used  as  oxidising  agent,  ethyl 
alcohol  itself  gives  rise  to  notable  traces  of  formaldehyde.  Hinkel 
does  not  claim  to  be  able  to  detect  with  certainty  less  than  5%  of 
methyl  alcohol  in  ethyl  alcohol. 

For  the  detection  of  methyl  alcohol  in  commercial  formalin,  in  which 
it  commonly  occurs,  it  is  of  course  necessary  to  remove  the  formal- 
dehyde before  applying  the  red-hot  copper  test.  Many  methods  for 
effecting  this  removal  have  been  suggested,  and  perhaps  the  simplest 


METHYL   ALCOHOL.  91 

is  that  of  Leffmann  (Chem.  Zeit.,  1905,  29,  1086),  who  recommends 
simple  distillation  with  a  slight  excess  of  potassium  cyanide.  (See 
p.  93.)  The  distillate  should  be  tested  for  formaldehyde,  and  a 
second  distillation  is  generally  necessary.  Other  methods  will  readily 
suggest  themselves  to  any  chemist. 

Estimation  of  Methyl  Alcohol. — When  nothing  but  methyl  alcohol 
and  water  is  present,  the  proportion  of  the  former  may  be  obtained 
from  the  specific  gravity  by  reference  to  the  tables  which  precede. 

No  general  method  for  the  estimation  of  methyl  alcohol  exists. 
It  is  only  possible  to  describe  methods  which  are  applicable  to  the 
particular  mixtures  in  which  the  analyst  is  most  frequently  called 
upon  to  estimate  it.  For  example,  in  the  assay  of  commercial  wood 
naphtha  it  is  usual  to  convert  the  methyl  alcohol  into  methyl  iodide 
and  to  estimate  this.  As  all  methoxy-  and  ethoxy-compounds  yield 
volatile  iodides  under  the  conditions  of  the  experiment,  it  is  necessary 
to  correct  for  the  methyl  acetate  present  in  wrood  naphtha,  and  the 
method  is  clearly  useless  for  mixtures  of  methyl  and  ethyl  alcohols. 
On  the  other  hand,  the  best  method  yet  described  for  the  estimation  of 
methyl  alcohol  in  admixture  with  ethyl  alcohol  is  quite  inapplicable 
to  wood  naphtha,  since  it  depends  on  the  oxidation  of  the  methyl 
alcohol  to  carbon  dioxide  under  conditions  in  which  acetone  and 
methyl  acetate  are  similarly  oxidised. 

For  the  estimation  of  methyl  alcohol  in  wood  naphtha  the  following 
modification  of  KrelPs  method  is  adopted  in  the  British  Government 
Laboratory : 

"  22  grm.  of  coarsely-powdered  iodine  and  5  c.c.  of  distilled  water 
are  placed  in  a  small  flask  and  cooled  by  immersion  in  ice-cold  water. 
Then  5  c.c.  of  the  wood  spirit  (60.0°  o.p.)  are  added,  the  flask  corked, 
the  contents  gently  shaken,  and  allowed  to  remain  in  the  ice-cold  bath 
for  10  to  15  minutes. 

"When  well  cooled,  2  grm.  of  red  phosphorus  are  added  to  the 
mixture  of  spirit  and  iodine  in  the  flask,  and  the  latter  is  imme- 
diately attached  to  a  reflux  condenser. 

"The  reaction  soon  commences,  and  must  be  moderated  by  dipping 
the  flask  into  a  cold  water-bath.  (Spirit  may  be  lost  if  the  reaction 
is  too  violent.)  After  about  15  to  20  minutes,  when  all  action  appears 
to  have  ceased,  the  water-bath  under  the  flask  is  gradually  heated  to 
a  temperature  of  about  75°  (167°  F.),  and  the  flask  being  occasionally 
shaken  is  allowed  to  remain  at  this  temperature  for  15  to  20  minutes. 


•92  ALCOHOLS. 

The  source  of  heat  is  then  removed  and  the  apparatus  left  for  an 
hour  till  it  has  cooled,  when  the  condenser  is  reversed,  and  the  methyl 
iodide  slowly  distilled  off — first  at  a  low  temperature — the  bath  being 
.allowed  to  boil  towards  the  end  of  the  operation  only.  The  end  of 
the  condenser  dips  into  water  in  a  measuring  tube,  and  the  iodide  is 
collected  under  water  and  measured  at  a  temperature  of  60°  F. 
"The  percentage  by  volume  is  found  from  the  formula: 

•c.c.  methyl  iodide  found  Xo. 647X100 

_  =  percentage  of  methyl  alcohol, 
c.c.  wood  spirit  taken 

"  Or  when  5  c.c.  of  spirit  are  taken: 

c.c.  methyl  iodide X 12. 94  =  percentage  by  volume. 

"  Ester,  and  acetals,  also  yield  methyl  iodide  by  this  process,  and 
from  the  percentage  of  methyl  alcohol  calculated  as  above  an  amount 
equivalent  to  the  percentage  of  these  substances  present  must  be 
deducted.  Practically,  however,  methyl  acetate  is  the  only  com- 
pound usually  found  in  quantity  sufficient  to  materially  affect  the 
result.  The  number  of  grm.  of  methyl  acetate  per  100  c.c.  of  spirit 
multiplied  by  0.5405  gives  the  equivalent  of  methyl  alcohol  to  be  de- 
•ducted  from  the  total  percentage  by  volume  calculated  from  the 
methyl  iodide  found." 

The  accuracy  of  the  method  is  limited  by  the  accuracy  with  which 
the  6  c.c.  or  so  of  methyl  iodide  can  be  measured.  Methyl  iodide 
is  not  quite  insoluble  in  water,  and  it  has  been  suggested  that  a  cor- 
rection for  this  solublity  and  for  the  vapour  which  remains  in  the 
^apparatus  should  be  made  once  for  all  by  distilling  6  c.c.  of  pure 
methyl  iodide  and  noting  the  deficiency  from  6  c.c.  of  the  distillate. 
On  the  other  hand,  some  of  the  acetone  which  distils  over  remains 
dissolved  in  the  methyl  iodide;  the  volume  so  dissolved  is  small  if  the 
distillation  be  conducted  as  above  described,  but  it  does  to  some 
•extent  compensate  for  the  loss  of  methyl  iodide  and  perhaps  renders 
unjustifiable  any  such  refinement  as  the  correction  referred  to. 

Theoretically,  all  the  sources  of  error  enumerated  above  would  be 
avoided  by  having  recourse  to  Zeisel's  method  for  the  estimation  of 
methoxy-groups,  in  which  the  whole  of  the  methyl  iodide  vapour  is 
swept  out  of  the  apparatus  by  a  current  of  carbon  dioxide  and  decom- 
posed by  alcoholic  silver  nitrate  solution  yielding  silver  iodide  which 
can  be  weighed  with  any  degree  of  accuracy  desired.  Stritar  and 
Zeidler  (Zeit.  anal.  Chem.,  1904,  43,  387)  have  advocated  this  pro- 


METHYL   ALCOHOL.  95 

cedure,  and  have  suggested  some  simplification  of  Zeisel's  apparatus. 
Duplicate  analyses,  however,  differ  by  i%  so  that  this  tedious  gravi- 
metric method  has  little  cause  to  be  preferred  on  the  score  of  accuracy 
to  the  simpler  volumetric  one. 

The  Estimation  of  Methyl  Alcohol  in  Formaldehyde  solutions 
is  sometimes  necessary.  It  may  be  present  to  the  extent  of  nearly 
20  per  cent.  Distillation  with  some  reagent  which  forms  non-vola- 
tile compounds  with  aldehydes  and  is  itself  non-volatile,  (see  page 
90),  will  suggest  itself,  but  there  are  practical  difficulties.  A  large 
quantity  of  the  reagent  is  required  and  the  best,  sodium  phenyl- 
hydrazine  sulphonate  (Hewitt's  reagent),  is  costly.  Gnehm  and 
Kaufler  (Zeit.  angew.  Chem.,  1904,  17,  673)  use  sodium  sulphanilate, 
90  grm.  of  which  they  add  gradually  to  25  c.c.  of  water  which  is  kept 
boiling  till  all  is  dissolved.  The  flask  containing  the  mixture  is 
rapidly  cooled,  the  contents  being  all  the  time  stirred  with  a  rod.  To- 
the  crystalline  mass  20  c.c.  of  the  formalin  is  added,  the  flask  corked 
and  left  three  or  four  hours.  The  mixture  is  next  submitted  to  dis- 
tillation and  the  first  35  c.c.  of  the  distillate  collected.  This  is  diluted 
to  50  c.c.  and  its  sp.  gr.  taken. 

The  following  method  (Duyk,  Ann.  Chim.  anal.,  1901,  6,  407)  is  in 
use  in  the  Paris  municipal  laboratory. 

To  100  c.c.  of  the  sample,  diluted  with  50  c.c.  of  iced  water,  ammo- 
nia solution  is  added  drop  by  drop  until  present  in  slight  excess. 
The  liquid  should  be  alkaline  to  phenolphthalein  after  standing 
some  hours;  if  not  alkaline,  more  ammonia  is  added.  After  ad- 
dition of  sodium  carbonate  to  render  the  hexamethylenetetramine 
more  stable,  the  liquid  is  distilled  until  100  c.c.  has  been  collected. 
This  distillate  is  neutralised  with  dilute  sulphuric  acid  and  fractionated 
through  a  "pear"  still-head  and  the  fraction  passing  over  between  65° 
and  100°  collected.  This  is  again  fractionated  so  as  to  obtain  a 
distillate  containing  approximately  75%  of  methyl  alcohol.  In  the 
final  distillate  the  methyl  alcohol  is  estimated  by  converting  it  into- 
methyl  iodide  as  already  described.  The  second  fractionation  might  be 
avoided  and  the  process  greatly  simplified  by  diluting  {he  distillate 
from  sulphuric  acid  to  some  exact  volume  and  determining  the  methyl 
alcohol  present  from  the  specific  gravity. 

A  recent  method,  based  on  a  different  principle,  is  that  of  Blank  and 
Finkenbeiner  (Ber.,  1906,  39,  i327)-  I  grm-  of  the  formalin  is- 
mixed  with  50  c.c.  of  twice  normal  chromic  acid  (66.7  grm.  chromic 


94  ALCOHOLS. 

acid  (H2CrO4)  per  1000  c.c.)  and  20  c.c.  of  pure  concentrated  sul- 
phuric acid  (98%),  and  allowed  to  stand  12  hours,  after  which 
the  mixture  is  diluted  to  1000  c.c.  To  50  c.c.  of  the  diluted  mixture 
a  small  crystal  of  potassium  iodide  is  added,  and  the  solution  titrated 
back  with  N/io  thiosulphate. 

EXAMPLE. — 50  c.c.  of  the  diluted  solution,  to  which  potassium 
iodide  had  been  added,  required  not  50  c.c.,  but  only  15  c.c.  of 
N/io  thiosulphate.  That  is  to  say,  oxygen  equivalent  to  35  c.c. 
of  the  thiosulphate  has  been  used  up  in  oxidising  the  formal- 
dehyde and  methyl  alcohol  contained  in  0.05  grm.  of  the  sample, 
or  (35X1.6  =  )  56  grm.  oxygen  per  100  grm.  of  the  sample.  The 
latter  was  known  to  contain  40  %  of  formaldehyde,  40  grm.  of 

which    require  — *»    42.7     grm.     oxygen.     As    methyl    alcohol 

3° 

requires  for  its  oxidation  one  and  a  half  times  its  weight  of  oxygen,  the 
percentage  of  methyl  alcohol  in  the  sample  is  §  (56.0  —  42.7)  = 
8.9%.  The  whole  process  can  be  completed  in  two  hours  if  the 
oxidation  be  assisted  by  warming  after  the  first  violent  action  is 
over,  but  great  care  is  necessary  and  the  solution  must  not  be  evapo- 
rated below  two-thirds  its  initial  bulk. 

For  the  estimation  of  methyl  alcohol  in  presence  of  ethyl  alcohol, 
the  method  of  Thorpe  and  Holmes  (Trans.  Chem.  Soc.,  1904,  85,  i)  is 
accurate,  occupies  but  little  of  the  analyst's  time,  and  can  be  con- 
ducted in  any  laboratory.  One  other  method  will  be  described,  as  it 
is  more  rapid  and  in  certain  concentrations  quite  as  accurate,  but  it 
depends  on  the  use  of  an  instrument  which  is  not  to  be  found  in 
every  laboratory.  The  method  of  Thorpe  and  Holmes  depends  on 
the  complete  oxidation  of  methyl  alcohol  to  carbon  dioxide  by  means 
of  chromic  acid  mixture.  Ethyl  alcohol  under  the  conditions  of  the 
experiment  yields  carbon  dioxide  equivalent  to  0.5  %  of  its  weight. 
The  process  is  as  follows: 

"The  sample  is  mixed  with  water  in  such  proportions  that  50  c.c.  of 
the  mixture  shall  contain  not  more  than  i  grm.  of  methyl  alcohol,  and 
in  the  presence  of  ethyl  alcohol  not  more  than  4  grm.  of  the  mixed 
alcohols.  50  c.c.  of  this  mixture  are  then  introduced  into  a  300 
c.c.  flask,  which  can  be  closed  by  a  ground-in  stopper  and  which 
is  fitted  with  a  funnel  and  side  tube.  20  grm.  of  potassium  di- 
chromate  and  80  c.c.  of  dilute  sulphuric  acid  (1:4)  are  added,  and 
the  mixture  allowed  to  remain  18  hours.  A  further  quantity  of  10  grm. 


METHYL   ALCOHOL. 


95 


of  potassium  dichromate  and  50  c.c.  of  sulphuric  acid  mixed  with 
an  equal  volume  of  water  are  now  added,  and  the  contents  of  the 
flask  heated  to  the  boiling-point  for  about  10  minutes,  the  evolved 
carbon  dioxide  being  swept  out  of  the  apparatus  by  a  current  of  air  and 
collected  in  soda-lime. 

"When  ethyl  alcohol  is  present,  a  subtractive  correction  must  be 
applied  to  the  weight  of  carbon  dioxide  thus  obtained  in  the  pro- 
portion of  o.oi  grm.  of  carbon  dioxide  for  each  grm.  of  ethyl  alcohol 
present." 

As  in  most  cases  the  liquid  to  be  examined  will  contain  at  least  10 
times  as  much  ethyl  alcohol  as  methyl  alcohol,  the  total  alcoholic 
content  may  be  determined  writh  sufficient  accuracy  from  the  sp.  gr. 
by  reference  to  the  ethyl  alcohol  tables. 

In  the  above-described  oxidation  process  acetone  and  methyl 
acetate  are  converted  into  acetic  acid  and  carbon  dioxide,  while  allyl 
alcohol  is  wholly  oxidised  yielding  carbon  dioxide.  As  the  pro- 
portion of  these  substances  in  wood  naphtha  used  for  methylating  in 
Great  Britain  is  fairly  constant,  and  as  none  of  them  are  normal  con- 
stituents of  commercial  ethyl  alcohol,  the  fact  that  they  take  part  in 
the  reaction  is  of  less  importance  where  the  object  is  to  detect  methyl- 
ated spirit  in  tinctures  or  to  estimate  the  proportion  of  wood  naphtha 
in  a  sample  of  methylated  spirit.  The  bulk  of  the  secondary  constitu- 
ents of  wood  naphtha  may  be  removed  from  the  spirit  by  shaking  with 
light  petroleum  and  saturated  salt  solution;  the  alcohols  are  then 
recovered  from  the  saline  layer  by  distillation  and  submitted  to  the 
oxidation  process.  Even  with  this  treatment  the  methyl  alcohol  will 
commonly  be  overestimated  by  4%  that  is  to  say,  5.2%  will  be  found 
where  only  5  %  is  present. 

For  the  estimation  of  methylated  spirit  in  tinctures,  Thorpe  and 
Holmes  recommend  that  the  spirit  from  25  c.c.  of  the  sample,  or  from 
50  c.c.  if  it  contains  less  than  50  per  cent,  of  alcohol,  be  treated  with 
light  petroleum  to  remove  essential  oils,  etc.,  as  described  in  a  later 
subsection  (Estimation  of  Alcohol  in  Essences)  and  then  distilled  and 
diluted  with  water  to  a  volume  of  250  c.c. ;  50  c.c.  of  this  mixture  is  then 
oxidised  with  chromic  acid  mixture  as  above  described.  If  the  weight 
of  carbon  dioxide  thus  obtained  does  not  exceed  o.oi  grm.  for  each 
gram  of  alcohol  present,  this  amount  being  equivalent  to  0.7  volume  of 
methyl  alcohol  in  100  volumes  of  the  alcohol,  then  it  may  be  concluded 
that  the  sample  contains  only  spirits  of  wine.  Should  the  amount  of 


96  ALCOHOLS. 

carbon  dioxide  exceed  this  amount,  its  equivalent  in  methyl  alcohol 
by  volume  must  be  subjected  to  a  subtractive  correction  of  from  0.7 
to  i%  (depending  on  the  amount  of  methylated  spirit  present),  the 
the  percentage  of  methylated  spirit  being  calculated  on  the  assumption 
that  the  quantity  of  methyl  alcohol  occurring  in  dehydrated  methylated 
spirit  does  not  exceed  8.8%. 

An  entirely  different  method  's  that  of  Leach  and  Lythgoe  (/.  Amer. 
Chem.  Soc.j  1905,  27,  964).  It  is  based  on  the  use  of  the  Zeiss  immer- 
sion refractometer,  and  when  this  instrument  is  available  it  affords  the 
most  rapid  means  of  estimating  methyl  alcohol  in  presence  of  ethyl 
alcohol.  With  the  immersion  refractometer  at  20°,  distilled  water 
gives  a  reading  of  14.5  scale  divisions.  Addition  of  ethyl  alcohol 
increases  the  reading;  until  at  about  75  %  alcohol  a  maximum  of 
10 1  divisions  is  reached  further  addition  of  alcohol  reduces  the 
reading  until  at  100%  alcohol  it  has  fallen  to  91.  Small  addi- 
tions of  methyl  alcohol  to  water  also  increase  the  readings  of  the 
instrument,  but  to  a  lesser  degree,  and  a  maximum  is  reached  at 
50%  alcohol  when  the  reading  is  39.8;  further  addition  of  methyl 
alcohol  reduces  the  reading,  so  that  at  91%  it  is  again  14.9  or 
about  the  same  as  pure  water,  while  at  100%  alcohol  the  reading 
is  only  2  divisions.  Leach  and  Lythgoe  give  two  tables,  of  which  one 
is  here  reproduced,  and  an  example  of  its  use  follows.  The  table 
shows  the  reading  of  the  immersion  refractometer  corresponding  to  each 
percentage  of  alcohol,  both  ethyl  and  methyl,  by  weight,  all  readings 
being  taken  at  exactly  20°.  This  table  will  show  at  a  glance  whether  a 
solution  of  given  strength  of  alcohol,  as  determined  from  the  sp.  gr., 
contains  ethyl  or  methyl  alcohol  or  is  a  mixture  of  the  two. 

For  the  estimation  of  methylated  spirit  in  tinctures  and  essences 
it  is  necessary  to  obtain  the  alcohols  free  from  non-volatile  matters 
and  from  essential  oils  before  subjecting  them  to  refractometric  treat- 
ment. Leach  and  Lythgoe  dilute  50  c.c.  to  200  c.c.,  treat  with  mag- 
nesia, filter,  distil  100  c.c.  of  the  filtrate  and  make  the  volume  of  the 
distillate  up  to  100  c.c.  The  method  of  Thorpe  and  Holmes  (see 
Estimation  of  Alcohol  in  Essences  and  Tinctures),  in  which  the 
tincture  is  mixed  with  salt  solution  and  the  oils,  etc.,  extracted  with 
light  petroleum,  is  preferable,  as  this  treatment  removes  most  of  the 
acetone  as  well.  By  either  of  these  methods  the  estimation  of  methyl 
alcohol  is  combined  with  that  of  ethyl  alcohol  and  only  requires  the 
refractometric  reading  to  be  made  on  the  distillate,  the  sp.  gr. 


METHYL   ALCOHOL. 


97 


SCALE  READINGS  ON  ZEISS  IMMERSION  REFRACTOMETER  AT  20°. 
Corresponding  to  each  %  by  weight  of  Ethyl  and  Methyl  Alcohol. 


Per  Cent, 
alcohol 
by  Weight. 

Scale  Readings. 

Per  Cent. 
Alcohol 
by  Weight. 

Scale  Readings. 

Methyl 
Alcohol. 

Ethyl 
Alcohol. 

Methyl 
Alcohol. 

Ethyl 
Alcohol. 

0 

14-5 

14-5 

5° 

39-8 

90-3 

i 

.8 

16.0 

5i 

•7 

91.! 

2 

15-4 

17.6 

52 

.6 

.8 

3 

16.0 

19.1 

53 

.6 

92.4 

4 

.6 

20.7 

54 

•5 

93  -° 

5 

17.2                  22.3 

55 

•4 

.6 

6 

.8 

,24.1 

56 

.2 

94.1 

7 

18.4 

25-9 

57 

.0 

•7 

8 

19.0 

27.8 

58 

38.6 

95-2 

9 

.6 

29.6 

59 

•3 

•7 

10 

2O.  2 

3J-4 

60 

37-9 

96.2 

ii 

.8 

33-2 

61 

•  5 

•  7 

12 

21.4 

35-° 

62 

.0 

97.1 

13 

22.0 

36.9 

63 

36.5 

•5 

14 

.6 

38.7 

64 

.0 

98.0 

*5 

23-2 

40-5 

65 

35-5 

•3 

16 

•9 

42.5 

66 

.0 

•7 

i? 

24-5 

44-5 

67 

34-5 

99.1 

18 

25.2 

46.5 

68 

.0 

•4 

19 

.8                  48.5 

69 

33-5         !             -7 

20 

26.5 

5°-5 

70 

.0 

IOO.O 

21 

27.1 

52.4 

7i 

32.3 

.2 

22 

.8 

54.3 

72 

3i-7 

•4 

23 

28.4 

56.3 

73 

.1 

.6 

24 

29.1 

58-2 

74 

3°-4 

.8 

25 

29.7 

60.  i 

75 

29.7 

IOI.O 

26 

30-3 

61  .9 

76 

.0 

.0 

27 

•9 

63-7 

77 

28.3 

100.9 

28 

31.6 

65-5 

78 

27.6 

•9 

29 

32-2 

67  .2 

79 

26.8 

.8 

3° 

.8 

69.0 

80 

.0 

•7 

31 

33-5                  7°-4 

81 

25-1 

.6 

32 

34-i                  7i-7 

82 

24.3 

•5 

33 

•7 

73-1 

83 

23.6 

•4 

34 

35-2 

74-4 

84 

22.8 

•3 

35 

.8 

75-8 

85 

21.8 

.1 

36 

36.3 

76.9 

86 

20.8 

99-8. 

37 

.8 

78.0 

87 

19.7 

•5 

38 

37-3 

79.1 

88 

18.6 

.2 

39 

•7 

80.2 

89 

J7-3 

98.9 

40 

38.1 

81.3 

90 

16.1 

.6 

4i 

-4 

82.3 

91 

14.9 

.3 

42 

.8 

83-3 

92 

13-7 

97-8 

43 

39-2 

84.2 

93 

12.4 

.2 

44 

•  3 

85-2 

94 

II  .0 

96.4 

45 

•  4 

86.2 

95 

9.6 

95-7 

46 

•5 

87.0 

96 

8.2 

94-9 

47 

.6 

.8 

97 

6.7 

.0 

48 

•  7 

88.7 

98 

5-1 

93-o 

49 

.8 

89-5 

99 

3-5 

92.0 

100                            2.0 

91.0 

Vol.  I.— 7 


98  ALCOHOLS. 

of  which  has  been  taken  to  ascertain  the  total  alcoholic  strength. 
But  where  it  is  required  to  estimate  small  amounts  of  methylated 
spirit  by  the  refractometer,  it  is  well  to  redistil  the  distillate  obtained 
by  either  of  these  methods  and  collect  only  the  first  50  .c.c.  or  even 
25  c.c.  The  sp.  gr.  may  show  that  a  little  alcohol  has  been  lost,  but  a 
liquid  is  obtained  of  greater  alcoholic  strength  which  enables  a  part  of 
the  table  to  be  used  in  which  the  readings  of  methyl  and  ethyl  alcohols 
differ  more  widely. 

EXAMPLE. — An  orange  extract  was  diluted  four  times  with  water, 
treated  with  magnesia  and  filtered.  A  measured  portion  of  the 
filtrate  was  then  distilled  and  the  distillate  made  up  to  the  measured 
portion  taken.  This  distillate  was  found  to  have  a  sp.  gr.  of  0.9754 
corresponding  to  16.91%  by  weight,  and  to  have  a  refraction  of  42.0 
on  the  Zeiss  immersion  refractometer.  By  interpolation  in  the  table, 
the  readings  of  ethyl  and  methyl  alcohol  corresponding  to  16.91  % 
alcohol  are  44.3  and  24.45,  respectively  the  difference  being  19.85. 
44.3—42.0  =  2.3.  100(2.3  -f-  19.85)=  ii. 6.  Thus  n.6%  of  the 
alcohol  present  was  methyl  alcohol. 

The  following  method,  due  to  Riche  and  Bardy  (Compt.  rend., 
1875,  80,  1076),  though  long  and  slow,  is  still  valued  by  many  ex- 
perienced chemists.  It  depends  on  the  formation  of  methyl  aniline 
violet.  10  c.c.  of  the  sample  of  alcohol, previously  rectified  if  necessary 
over  potassium  carbonate,  placed  in  a  small  flask  with  15  grm.  of 
iodine  and  2  grm.  of  red  phosphorus.  Methyl  and  ethyl  iodides  are 
formed  and  should  be  distilled  off  into  about  30  c.c  of  water.  The 
heavy  oily  liquid  which  settles  in  the  receiver  is  separated  and  trans- 
ferred to  a  flask  containing  5  c.c.  of  aniline.  The  flask  should  be 
placed  in  cold  water,  if  the  action  is  violent;  or,  if  necessary,  the  re- 
action may  be  stimulated  by  gently  warming  the  flask.  After  one 
hour  the  product  is  boiled  with  water  and  solution  of  rodium  hydrox- 
ide added,  when  the  bases  rise  as  an  oily  layer,  which  may  be  drawn 
off  with  a  pipette  after  filling  the  flask  with  water  up  to  the  neck, 
i  c.c.  of  this  oily  liquid  is  oxidised  by  adding  it  to  10  grm.  of  a  mix- 
ture of  100  parts  of  clean  sand,  2  of  common  salt,  and  3  of  copper 
nitrate.  After  being  thoroughly  mixed,  the  mass  is  introduced  into 
a  glass  tube  and  heated  to  90°  for  eight  or  ten  hours.  The  product 
is  exhausted  with  warm  alcohol,  the  liquid  filtered,  and  made  up  with 
alcohol  to  100  c.c.  If  the  sample  of  spirit  was  pure,  the  tint  of  the 
liquid  is  red,  but  in  presence  of  i%  of  methyl  alcohol  it  has  a  distinct 


WOOD    NAPHTHA.  99 

violet  shade;  with  2.5%  the  shade  is  very  distinct,  and  still  more  so 
with  5%.  To  detect  more  minute  quantities  of  methyl  alcohol,  dilute 
5  c.c.  of  the  colored  liquid  to  ico  c.c.  with  water,  and  5  c.c.  of  this 
again  to  400  c.c.  The  liquid  thus  obtained  is  heated  in  porcelain, 
and  a  piece  of  undyed  wool  (8  cm.  square  is  a  convenient  size)  is  im- 
mersed. The  fabric  should  be  cleaned  before  use  with  warm  soap 
suds,  washed  thoroughly,  and  dried.  It  is  stated  that  for  this  test 
the  wool  should  be  free  from  sulphur.  The  wool  should  be  left  in 
the  liquid  to  be  tested  for  about  thirty  minutes,  then  washed  and 
dried.  Pure  alcohol  will  not  produce  a  dye,  but  methylated  alcohol 
will  produce  a  violet,  the  depth  of  tint  giving  approximate  indication 
of  the  proportion  present.  Comparison  slips,  made  with  i,  2,  3  and 
5%  of  methyl  alcohol  should  be  prepared  as  standards. 

WOOD  NAPHTHA.     WOOD  SPIRIT. 

In  addition  to  methyl  alcohol  and  water,  commercial  wood  naphtha 
contains  acetone  and  higher  ketones  (nil  to  14%),  esters,  mainly 
methyl  acetate  (nil  to  4%),  together  with  smaller  proportions  of  allyl 
alcohol,  pyridine  and  other  substances. 

For  use  in  the  colour  industry  a  very  pure  spirit  is  required,  acetone 
being  a  highly  objectionable  impurity,  and  as  a  consequence  an 
acetone-free  grade  of  spirit  is  now  a  regular  article  of  commerce. 
For  dissolving  resins  to  make  varnishes,  the  presence  of  acetone  is  an 
advantage  on  account  of  its  solvent  properties.  As  a  denaturant  of 
ethyl  alcohol,  the  proportion  of  nauseous  constituents — allyl  alcohol, 
pyridine,  etc. — is  most  important. 

ASSAY   OF    WOOD    NAPHTHA. 

The  methods  now  to  be  described  are  applicable  not  only  to  crude  or 
partially  purified  naphtha,  but  to  any  commercial  sample  of  wood 
spirit.  The  impurities  to  be  looked  for  and  estimated  are  the  same  in 
every  grade  of  spirit  up  to  the  so-called  acetone-free  grade;  the  various 
grades  differ  only  in  the  amount  of  the  secondary  constituents,  with 
the  reservation  that  some  crude,  usually  high-coloured,  naphthas 
contain  impurities  of  high  boiling-point  (150-200°  and  over),  hydro- 
carbons, acids  and  bases,  which  are  scarcely  detectable  in  spirit  of 
average  quality. 


100  ALCOHOLS. 

Estimation  of  Methyl  Alcohol.— The  British  Government 
Laboratory  method  has  been  given  in  an  earlier  subsection  (p.  91). 

Estimation  of  Acetone  and  Higher  Ketones. — These  are  best 
estimated  by  Messenger's  method  (Ber.,  1888,  21,3366)  and  calculated 
as  acetone.  The  method  is  rapid  and  with  solutions  of  pure  acetone 
in  water  or  methyl  alcohol  gives  excellent  results.  Applied  to  wood 
naphtha  it  is  less  satisfactory;  the  whole  of  the  acetone  reacts  no  doubt, 
so  that  the  number  obtained  is  not  less  than  the  amount  of  real  acetone 
present.  Certain  higher  ketones,  which  are  present,  also  take  part  in 
the  reaction,  but  reduce  a  smaller  amount  of  iodine  per  unit  of  weight 
than  does  acetone,  so  that  the  number  obtained  is  lower  than  the  true 
amount  of  ketones  present.  The  method  is,  however,  as  good  as 
any  and  the  quickest  yet  described.  That  of  Deniges  (Bull.  Soc. 
chim.,  1899  (v),  19,754),  based  upon  the  formation  of  an  insoluble 
compound  of  acetone  with  mercuric  sulphate,  is  open  to  similar  ob- 
jection and  it  occupies  more  time.  Messenger's  method  is  followed 
with  but  slight  modification  in  the  Br  tish  Government  Laboratory, 
where  the  following  procedure  is  adopted: 

"25  c.c.  of  N/i  sodium  hydroxide  are  placed  in  a  stoppered 
flask  of  about  200  c.c.  capacity.  To  this  is  added  0.5  c.c.  of  the 
naphtha.  The  mixture  is  well  shaken  and  allowed  to  stand  5 
to  10  minutes.  Into  it  from  a  burette  N/5  iodine  solution  is  run 
slowly,  drop  by  drop,  vigorously  shaking  all  the  time,  till  the  upper 
portion  of  the  solution,  on  standing  a  minute,  becomes  quite  clear. 
A  few  c.c.  more  of  N/5  iodine  solution  are  added,  as  to  get  concord- 
ant results  an  excess  of  at  least  25%  of  the  iodine  required  must  be 
added.  After  shaking,  the  mixture  is  allowed  to  stand  for  10  to  15 
minutes,  and  then  25  c.c.  N/i  sulphuric  acid  are  added.  The  ex- 
cess of  iodine  ^is  liberated,  titrated  with  N/  10  sodium  thiosulphate 
solution  and  starch,  and  half  the  number  of  c.c.  of  thiosulphate  solu- 
tion used  are  deducted  from  the  total  number  of  c.c.  of  iodine  so  ution 
used.  The  difference  gives  the  amount  of  acetone  by  weight  in  the 
naphtha  by  the  formula:  c.c.  N/5  iodine  solution  required  X  0.387  = 
grm.  of  acetone  per  100  c.c.  of  wood  naphtha. 

"This  includes  as  acetone  any  aldehydes,  etc.,  capable  of  yielding 
iodoform  by  this  reaction. 

"If  the  quantity  of  'acetone'  is  excessive,  a  less  quantity  of  the 
spirit  is  taken,  or  10  c.c.  are  diluted  with  10  c.c.  of  methyl  alcohol 
free  from  acetone,  and  0.5  c.c.  of  the  mixture  is  used." 


WOOD    NAPHTHA.  IOI 

Messenger  in  his  original  communication  calls  attention  to  the  fact 
that  commercial  sodium  hydroxide  may  contain  nitrite,  which  must  be 
allowed  for.  This  is  easily  done  by  adding  a  crystal  of  potassium 
iodide  to  25  c.c.  of  the  N/i  sodium  hydroxide,  acidifying  and  titrat- 
ing against  the  standard  thiosulphate.  It  is,  however,  not  difficult  to 
obtain  sodium  hydroxide  which  is  practically  free  from  every  impurity 
except  water. 

Estimation  of  Esters. — To  5  c.c.  of  the  naphtha  contained  in  a 
small  Jena  glass  flask,  20  c.c.  of  recently  boiled  distilled  water  are  added, 
and  then  10  c.c.  of  N/i  sodium  hydroxide  and  the  whole  heated  for 
two  hours  under  a  reflux  condenser  on  the  water-bath.  The  liquid 
is  then  cooled,  phenolphthalein  added  and  the  excess  of  sodium 
hydroxide  titrated  with  N/i  acid. 

Let  the  amount  of  acid  required  be  x  c.c.  Then  the  number  of 
grm.  of  esters  (calculated  as  methyl  acetate)  in  100  c.c.  of  the  sample 
is  1.48  (10  —  x).  If  the  proportion  of  esters  is  very  small  and  it  is 
required  to  estimate  them  with  great  accuracy,  a  much  larger  quantity 
of  spirit  may  be  taken,  and  N/io  alkali  and  acid  used,  but  in  this 
case  the  spirit  should  be  first  boiled  under  a  reflux  condenser  to 
expel  carbon  dioxide.  Wood  spirit  is  generally  almost  neutral  to 
phenolphthalein,  but  if  not  it  must  of  course  be  rendered  neutral 
before  proceeding  to  the  estimation  of  esters.  In  the  British  Govern- 
ment Laboratory  the  hydrolysis  of  the  esters  is  conveniently  effected 
in  a  silver  pressure  flask  of  about  150  c.c.  capacity. 

Bromine  Test  for  Unsaturated  Compounds.— No  accurate 
method  for  the  estimation  of  allyl  alcohol  in  wood  naphtha  exists,  but 
the  amount  of  bromine  which  the  naphtha  will  decolourise  is  some 
measure  of  the  unsaturated  compounds,  of  which  allyl  alcohol  is 
known  to  be  one  commonly  present.  For  denaturing  spirits  of  wine 
in  Britain,  wood  naphtha  is  required  to  have  a  certain  minimum 
capacity  for  decolourising  bromine;  not  more  than  30  c.c.  of  the  naphtha 
must  be  necessary  to  decolourise  0.5  grm.  bromine.  The  test  is  con- 
ducted as  follows: 

A  standard  bromine  solution  is  made  by  dissolving  12.406  grm.  of 
potassium  bromide  and  3.481  grm.  of  potassium  bromate  in  a  litre 
of  recently  boiled  distilled  water. 

50  c.c.  of  this  standard  solution  (=0.5  grm.  bromine)  are  placed 
in  a  flask  of  about  200  c.c.  capacity,  having  a  well-ground  stopper. 
To  this  is  added  10  c.c.  of  dilute  sulphuric  acid  (i  in  4)  and  the  whole 


102  ALCOHOLS. 

shaken  gently.  After  standing  for  a  few  minutes  the  wood  naphtha 
is  slowly  run  from  a  burette  into  the  clear  brown  solution  of  bromine 
until  the  latter  is  completely  decolourised. 

Estimation  of  Basic  Substances. — These  (pyridines,  mono-, 
di-,  and  trimethylamine,)  can  be  to  some  extent  measured  by  the 
methyl-orange  alkalinity  of  the  sample,  though  as  it  is  not  known  which 
base  predominates  it  is  not  usual  to  calculate  the  bases,  as  pyridine 
for  instance,  in  the  manner  in  which  the  ketones  are  calculated  as 
acetone  and  the  esters  as  methyl  acetate.  Fawsitt,  to  whom  we  owe 
much  of  our  information  concerning  wood  alcohol,  mentions  the 
methylamines,  but  not  pyridine,  which  is  certainly  present  in  most 
samples.  But  no  doubt  the  bases  in  naphthas  differ  with  the  source 
of  the  naphtha.  For  use  as  a  denaturant  in  Britain,  wood  naphtha 
must  comply  with  the  following  specification  as  to  reaction  with 
indicators: 

"The  naphtha  should  be  faintly  acid  to  phenolphthalein,  slightly 
alkaline  or  neutral,  rarely  acid  to  litmus,  and  always  alkaline  to  methyl 
orange.  25  c.c.  of  the  wood  naphtha  are  placed  in  each  of  two 
beakers,  and  titrated  with  N/io  acid,  using  in  one  case  a  few  drops 
of  litmus  solution,  and  in  the  other  of  a  solution  of  methyl  orange  as 
indicator.  With  litmus  usually  o.i  to  0.2  c.c.  of  N/io  acid  is  re- 
quired to  neutralise.  With  methyl  orange  the  total  alkalinity  should 
be  greater,  at  least  5  or  6  c.c.  of  N/io  acid  being  required  for  neu- 
tralisation. 

''The  total  alkalinity,  less  that  given  with  litmus,  is  the  'methyl 
orange  alkalinity'  and,  for  the  25  c.c.  of  wood  spirit,  should  not  be 
less  than  is  required  to  neutralise  5  c.c.  of  N/io  acid." 

Furfural  may  be  detected  by  adding  10  c.c.  of  the  naphtha  to  i  or 
2  c.c.  of  acetic  acid  in  which  a  few  drops  of  aniline  have  been  dissolved. 
Furfural  if  present  will  develop  an  intense  red,  but  as  acetic  acid 
contains  furfural  quite  as  often  as  wood  spirit  does,  the  acid  and  aniline 
must  be  mixed  first  and  must  remain  colourless  for  five  minutes  before 
the  spirit  is  added. 

Wood  spirit  occasionally  contains  i  %  or  more  of  substances  of  high 
boiling-point  (150°  to  200°  and  over)  which  may  be  separated  simply 
by  slow  distillation  of  a  large  quantity  on  the  water-bath.  As  the 
residue  is  tar,  the  method  to  be  adopted  for  its  further  examination 
must  be  looked  for  in  another  section.  This  tar  has  the  character- 
istic offensive  odor  of  crude  naphtha,  only  in  a  greater  degree.  Sepa- 


WOOD    NAPHTHA.  103 

rated  into  hydrocarbons,  phenolic  bodies  and  bases,  only  the  latter 
are  found  to  be  offensive;  the  hydrocarbons  have  the  odor  of  terpenes 
while  the  predominant  phenolic  body  is  no  doubt  guaiacol,  which 
alone  has  a  grateful  odour,  but  in  combination  with  pyridine  bases  it 
appears  to  make  their  offensive  odour  even  more  offensive. 

The  detection  of  small  admixtures  of  ethyl  alcohol  in  wood  spirit  is 
less  important  than  the  converse.  The  following  tests  have  been  pro- 
posed for  the  purpose: 

Berthelot  suggested  heating  the  sample  with  twice  its  volume  of 
concentrated  sulphuric  acid.  If  i  %  of  ethyl  alcohol  is  present,  ethy- 
lene  is  evolved,  and  may  be  absorbed  by  bromine  and  estimated  as 
ethylene  dibromide.  Acetone  and  the  normal  impurities  of  wood  spirit 
may  yield  carbon  monoxide  and  carbon  dioxide  but  not  ethylene. 

Riche  and  Bardy  (Compt.  rend.,  1876,  82,  768)  use  a  reaction  de- 
pendent on  the  production  of  aldehyde  from  ethyl  alcohol  by  oxidising 
agents,  and  the  action  of  aldehyde,  methylal,  acetal,  etc.,  on  salts  of 
rosaniline,  whereby  a  violet  coloring  matter  is  produced,  which  is  not 
destroyed  by  subsequent  addition  of  sulphurous  acid.  4  c.c.  of  the 
liquid  to  be  examined  are  mixed  with  6  c.c.  of  concentrated  sulphuric 
acid  and  10  c.c.  of  water.  7  or  8  c.c.  are  distilled  into  10  c.c.  of  water, 
and  to  this  liquid  are  added  5  c.c.  of  sulphuric  acid  and  10  c.c.  of  a 
solution  of  potassium  permanganate  of  1.028  sp.  gr.  After  five 
minutes  have  elapsed,  4  c.c.  of  a  solution  of  sodium  thiosulphate,  of 
1.29  sp.  gr.,  and  4  c.c.  of  a  solution  of  magenta,  containing  0.02  gram 
per  1000  c.c.  are  added.  Under  hese  conditions,  wood  spirit  un- 
mixed with  ethyl  alcohol  gives  a  yellowish-white  liquid  but  if  ethyl 
alcohol  is  present  the  solution  assumes  a  violet  color  of  greater  or  less 
intensity.  Acetone,  formic  acid,  and  isopropyl  alcohol  give  no  similar 
reaction. 

For  the  examination  of  a  reputed  high-grade  methyl  alcohol,  the 
above  tests  will  require  little  variation,  except  in  the  case  of  the  esters 
when  the  procedure  is  that  described  when  dealing  with  these.  Pure 
methyl  alcohol  should  of  course  be  neutral  to  both  phenolphthalein  and 
methyl  orange,  it  should  give  no  iodoform  reaction  and  it  should  not 
decolourise  bromine.  If  a  spirit  passes  all  these  tests,  its  content  of 
methyl  alcohol  may  safely  be  deduced  from  its  sp.  gr. 

The  specifications  with  which  wood  naphtha,  intended  for  methyl- 
ating,  has  to  comply  differ  considerably  in  Great  Britain  and  the 
United  States. 


104  ALCOHOLS. 

In  Great  Britain  the  wood  naphtha  must  be  sufficiently  impure  to 
impart  to  the  methylated  spirit  such  an  amount  of  nauseousness  as  will, 
in  the  opinion  of  the  Principal  of  the  Government  Laboratory,  render 
such  mixture  incapable  of  being  used  as  a  beverage  or  of  being  mixed 
with  potable  spirits  of  any  kind  without  rendering  them  unfit  for  human 
consumption.  It  must  conform  to  the  following  tests: 

a.  Not  more  than  jb  c.c.  should  be  required  to  decolourise  a  solution 
containing  0.5  grin,  of  bromine. 

b.  It  should  be  neutral  or  only  slightly  alkaline  to  litmus,  and  25  c.c. 
should  require  at  least  5  c.c.  of  N/io  acid  when  methyl  orange  is 
used  as  indicator. 

It  should  contain: 

a.  At  least  72  %  by  volume  of  methyl  alcohol. 

b.  Not  more  than  12  grm.  per  100  c.c.  of  acetone,  aldehydes  and 
higher  ketones,  estimated  as  "Acetone"  by  Messenger's  method. 

c.  Not  more  than  3  grm.  per  100  c.c.  of  esters,  estimated  as  methyl 
acetate  by  hydrolysis. 

In  the  United  States  the  colour  must  not  exceed  that  of  N/  5000  iodine 
solution,  the  sp.  gr.  must  not  exceed  0.830  at  6o°/6o°  F.,  and  90% 
should  distil  below  75°  at  760  mm.  Diluted  with  a  double  volume  of 
water,  the  naphtha  should  remain  clear  or  develop  only  a  slight  opal- 
escence.  The  "acetone  "  by  Messenger's  method  must  not  be  less  than 
15  nor  more  than  25  grm.  per  100  c.c.,  and  the  esters  must  not  exceed 
5  grm.  per  100  c.c.  Not  less  than  15,  nor  more  than  25  c.c.  should 
be  required  to  decolourise  a  solution  containing  0.5  grm.  of  bromine. 

ACETONE . 

Dimethyl-ketone,  CH3.CO.CH3. 

For  some  reason,  presumably  because  it  is  an  important  constituent 
of  wood  spirit,  acetone  has  found  its  wray  into  this  section  of  this  work, 
and  though  it  is  not  an  alcohol,  this  arrangement  is  continued  rather 
than  make  further  departure  from  the  original  plan. 

Acetone  is  a  colourless,  pleasant-smelling,  neutral  liquid,  miscible  in  all 
proportions  with  water,  methyl  alcohol  and  ethyl  alcohol.  It  is  said  to  be 
thrown  out  of  its  aqueous  or  alcoholic  solution  by  saturating  these 
with  calcium  chloride.  From  its  aqueous  or  dilute  alcoholic  solution 
this  is  more  or  less  true,  and  if  petroleum  spirit  is  added  the  separation 
is  fairly  complete  and  common  salt  may  replace  the  calcium  chloride. 


ACETONE. 

From  strong  methyl  alcohol  the  separation  by  means  of  calcium 
chloride  is  much  more  difficult  than  might  be  expected  from  the 
published  statements.  The  b.  p,  according  to  Fuchs  (Zeitsch.  angew. 
Chem.,  1898,  38,  870),  ranges  from  55.06  at  710°  mm.  to  58.16°  at 
790  mm.  The  m.  p.  according  to  Ladenburgand  Krugel  (Ber.,  1899, 
32,  1821),  is — 94.9°.  The  sp.  gr.  at  i5°/4°,  according  to  MacElroy 
and  Krug  (/.  Anal.  Chem.,  6,  187),  is  0.79726.  These  authors  give  a 
table  showing  sp.  gr.  at  i5°/4°of  aqueous  solutions  of  acetone  and  the 
table  has  been  reprinted  in  the  Chem.  Centr.,  1892,  2,  158,  and  in 
the  /.  Chem.  Soc.,  1893,  ^4,  i»  7- 

Detection  of  Acetone.— For  the  detection  of  acetone,  especially 
in  urine,  a  great  many  tests  have  been  described.  Only  three  will  be 
referred  to  here. 

Lichen's  Iodoform  Test. — Acetone  gives  the  iodoform  reaction 
in  the  cold  and,  in  the  probable  absence  of  other  substances,  such  as 
aldehyde  and  isopropyl  alcohol  which  behave  similarly,  the  formation 
of  iodoform  in  the  cold  is  useful  as  a  test  for  acetone.  To  2  c.c.  of  the 
liquid,  3  to  5  drops  of  10%  sodium  hydroxide  are  added  and  then, 
drop  by  drop,  N/ 2  iodine  solution  until  very  faintly  yellow.  In  the 
presence  of  acetone,  iodoform  separates  at  once. 

Legal's  Nitroprusside  Test.— To  5  c.c.  of  the  liquid  5  drops  of  a 
then  i  c.c.  of  10  %  sodium  hydroxide  solution.  In  presence  of 
freshly-prepared  solution  of  sodium  nitroprusside  are  added,  and 
acetone  the  liquid  assumes  an  orange  tint,  which  fades  to  clear  yellow 
in  15  to  20  minutes.  If  the  experiment  be  repeated  and  the  solution 
made  just  distinctly  acid  with  acetic  acid  immediately  after  the  addition 
of  the  alkali,  a  purplish-red  color  will  develop  in  presence  of  acetone, 
and  this  colour  remains  practically  unchanged  for  15  to  20  minutes. 
The  comparative  persistence  of  this  purple  color  (it  slowly  changes, 
becoming  more  blue)  serves  to  distinguish  acetone  from  higher  homo- 
logues  and  from  certain  other  substances  which  may  occur  in  urine. 

Salicylaldehyde  Test.— This  test  (¥rommer,Berl.klin.Wochensch., 
1905,  42,  1008)  is  said  to  be  the  most  delicate  yet  described.  It  is 
given  third  place  here,  because  salicylaldehyde,  unlike  iodine  and 
nitroprusside,  is  not  always  at  the  analyst's  command.  To  10  c.c. 
of  the  liquid  to  be  examined  i  grm.  of  solid  potassium  hydroxide 
is  added  and  then,  without  waiting  for  this  to  dissolve,  10  drops  of 
salicylaldehyde,  and  the  whole  warmed  to  70°.  In  the  presence  of 
acetone  a  purple-red  contact-ring  develops.  If  the  hydroxide  is  all 


106  ALCOHOLS. 

dissolved  before  the  addition  of  the  salicylaldehyde,  the  liquid  becomes 
yellow,  then  reddish,  and  finally  purple-red. 

Detection  of  Acetone  in  Urine. — R.  L.  Siau,  who  with  F.  W.  Paw 
has  done  perhaps  more  than  any  other  wrorker  in  this  field,  informs 
the  writer  that  the  detection  and  estimation  of  acetone  in  urine  has 
not  the  importance  which  the  voluminous  literature  might  suggest, 
but  since  the  analyst  is  frequently  asked  to  carry  out  such  tests,  the 
subject  must  be  dealt  with,  even  if  very  briefly.  For  an  exhaustive 
review  of  the  many  methods  which  have  been  described,  those  specially 
interested  are  referred  to  a  series  of  papers  by  Bohrisch  (Pharmaceut. 
Centralho,  1907,  48,  181,  206,  220,  and  245).  Bohrisch  recommends 
the  analyst  not  to  rely  on  any  one  test,  but  to  apply  two  or  three. 
The  salicylaldehyde  test  may  be  applied  to  the  urine  direct  and  it 
has  the  advantage  that  aceto-acetic  acid,  which  may  be  present  in 
pathologic  urine,  does  not  give  the  reaction.  If  no  red  or  reddish 
ring  develops,  but  only  a  yellow  colouration,  acetone  is  certainly  absent. 
On  the  other  hand,  the  reaction  is  so  sensitive  that  it  gives  no  idea  of 
the  quantity  present.  If  a  positive  result  is  obtained,  therefore,  a  less 
delicate  test  should  be  applied,  preferably  the  nitroprusside  test,  which 
may  also  be  applied  to  the  urine  direct  without  distillation  or  other 
previous  treatment.  A  positive  result  indicates  a  notable  quantity 
of  either  acetone  or  aceto-acetic  acid.  To  distinguish  between  these, 
many  methods  have  been  described.  Bohrisch  recommends  acidifying 
50  c.c.  of  the  urine  with  sulphuric  acid  and  shaking  with  25  c.c.  of 
ether.  The  ether  is  then  shaken  with  15  to  20  c.c.  of  water,  which 
will  then  contain  a  large  part  of  the  acetone  and  aceto-acetic  acid 
originally  present,  while  other  substances  which  interfere  with  the  tests 
subsequently  to  be  applied  are  got  rid  of.  The  aqueous  layer  is  freed 
from  dissolved  ether  by  warming  to  40°  with  frequent  shaking,  and  a 
portion  is  then  tested  for  aceto-acetic  acid  by  means  of  ferric  chloride. 
If  no  violet  colouration  results,  then  the  positive  reaction  with  nitro- 
prusside must  have  been  due  to  acetone.  But  if  aceto-acetic  acid  is 
shown  to  be  present,  the  remainder  of  the  ether-free  aqueous  extract 
is  tested  for  acetone  by  the  iodoform  test.  This  test  should  not  be 
applied  to  urine  direct,  because  other  substances  which  give  the 
reaction  may  be  present,  and  the  above-described  method  of  shaking 
out,  though  far  from  quantitative,  is  preferable  to  any  distillation 
method,  because  at  the  temperature  of  distillation  aceto-acetic  acid 
and  other  substances  may  be  decomposed,  i2lding  acetone. 


ACETONE.  107 

Estimation  of  Acetone. — Messenger's  volumetric  method  (de- 
scribed under  Assay  of  Wood  Spirit)  maintains  its  position  as  that 
most  frequently  applied.  In  common  with  every  other  method,  it 
gives  less  satisfactory  results  with  complex  mixtures  than  with  pure 
aqueous  or  alcoholic  solutions  of  acetone,  since  the  results  are  influ- 
enced by  the  presence  of  anything  \vhich  can  reduce  iodine  in  the  cold. 
It  is  more  accurate  as  well  as  more  expeditious  than  the  gravimetric 
method  of  Kramer  (Ber.,  1880,  13,  1000)  from  which  it  was  developed, 
though  a  return  to  this  is  periodically  recommended.  Its  critics,  as 
a  rule,  only  recommend  the  substitution  of  some  other  reducing  solu- 
tion for  the  thiosulphate,  whereas  what  is  needed  is  not  a  different 
solution,  but  a  sufficient  excess  of  iodine  and  time  for  the  reaction  to 
take  place.  The  British  Government  Laboratory  directions  for  carry- 
ing out  the  determination  are  reproduced  in  this  edition,  because  in 
those  directions  proper  account  has  been  taken  of  hese  factors. 

Method  of  Jolles. — This  author  (Ber.,  1906,  39,  1306)  has  found 
that  the  reaction,  CH3.CO.CH3  +  NaHSO3  =  CH3.C(OH)(SO3Na).CH3, 
proceeds  quantitatively  with  respect  to  the  acetone,  if  the  sulphite 
is  present  in  large  excess  and  sufficient  time  allowed,  and  on  this 
observation  has  based  the  following  method  for  the  estimation  of 
acetone: 

A  solution  of  sodium  hydrogen  sulphite  is  prepared  of  known  titre 
with  respect  to  iodine,  and  a  large  excess  (three  or  four  times  as  much 
as  is  likely  to  be  required)  added  to  a  measured  or  weighed  portion 
of  the  liquid  to  be  tested.  After  30  hours  the  excess  of  sulphite  is 
titrated  with  standard  iodine  solution.  One  mol.  of  sodium  hydro- 
gen sulphite  or  two  atoms  of  iodine  correspond  to  one  mol.  of  acetone. 

Method  of  Deniges.— (Compt.  rend.,  1898,  127,  963,  and  Bull. 
Soc.  chim.,  1899,  [v],  19,754.)  This  method  depends  on  the  quantita- 
tive formation  of  an  insoluble  compound  of  definite  composition  when 
acetone  is  treated  with  a  large  excess  of  mercuric  sulphate.  The 
reagent  is  prepared  by  dissolving  5  grm.  of  mercuric  oxide  in  100  c.c. 
of  water  to  which  20  c.c.  of  sulphuric  acid  has  been  added.  If  it 
is  desired  to  make  use  of  the  formula  given  by  Deniges  for  simplifying 
the  calculation  in  the  volumetric  modification  of  the  method,  it  is 
necessary  to  make  up  this  solution  so  that  each  100  c.c.  contains 
exactly  5  grm.  of  mercuric  oxide  or  preferably  to  carry  out  a  blank 
experiment.  The  liquid  under  examination  is,  if  necessary,  diluted 
with  water  until  its  content  of  acetone  is  reduced  to  0.2%;  the 


108  ALCOHOLS. 

content  of  methyl  alcohol  also  must  not  exceed  50%  nor  that 
of  ethyl  alcohol  2  %.  To  25  c.c.  of  the  diluted  liquid  25  c.c.  of 
of  the  mercury  reagent  is  added,  and  the  whole  heated  on  the  water- 
batii  for  ten  minutes.  After  cooling,  the  precipitate  is  collected  on  a 
tared  filter,  washed  with  not  more  than  100  c.c.  of  cold  water,  dried 
.at  100°.  and  weighed  as  3Hg5S2O11.4C3H6O).  The  weight  of  the 
precipitate  multiplied  by  0.0609  gives  the  weight  of  acetone  in  the 
25  c.c.  of  liquid  taken  for  the  experiment. 

Volumetric  modification  of  Deniges'  method.  This  depends 
on  the  use  of  a  mercury  solution  of  exactly  known  strength,  and  the 
estimation  of  the  mercury  remaining  in  the  filtrate  from  the  precipitate 
of  the  acetone  compound.  The  procedure  is  the  same  as  in  the 
^gravimetric  method  up  to  the  filtration,  except  that  the  volume  of 
reagent  taken  must  be  exactly  measured.  The  washing  of  the  pre- 
cipitate is  stopped  when  the  filtrate  and  washings  amount  to  nearly 
100  c.c.,  the  volume  made  up  exactly  to  100  c.c.  and  the  contents  of  the 
flask  shaken.  To  20  c.c.  of  this  liquid  mixed  with  15  c.c.  of  ammonia 
and  not  less  than  50  c.c.  of  water,  10  c.c.  of  potassium  cyanide  solution 
(13  grm.  cyanide  per  litre)  are  added.  This  is  rather  more  than 
equivalent  to  the  mercury  which  can  be  present  even  if  none  has  been 
removed  by  acetone.  If  much  mercury  has  been  removed  from  solu- 
and  this  excess  is  now  titrated  with  N/io  silver  nitrate,  using  potas- 
tion  by  acetone,  there  will  be  a  large  excess  of  potassium  cyanide, 
sium  iodide  as  indicator  until  there  is  a  slight  permanent  turbidity. 
If  n  be  the  number  of  c.c.  of  silver  solution  required  and  x  the  per- 
centage of  acetone  in  the  liquid,  of  which  25  c.c.  were  taken  for  the 
test,  then 

x  =  (n— 0.4)  X  0.31. 

In  this  formula  0.4  is  the  volume  of  silver  solution  which  would  be 
required  if  there  were  no  acetone  present  and  if  the  solutions  of 
potassium  cyanide  and  mercuric  sulphate  were  of  the  exact  strength 
stated.  As  these  solutions  will  rarely  be  exact  in  titre,  it  is  better  to 
carry  through  a  blank  experiment  with  the  measured  quantities 
stated,  but  no  acetone,  and  to  substitute  the  volume  of  silver  nitrate 
required  under  these  conditions  for  the  0.4  of  Deniges'  formula. 

Estimation  of  Acetone  in  Urine. — Distillation  and  estimation 
of  the  acetone  in  the  distillate  by  Messenger's  method  is  most 
usual.  Aceto-acetic  acid  if  present  will  be  decomposed  at  the  tern- 


ACETONE.  109 

perature  of  distillation,  yielding  acetone.  For  their  separate  esti- 
mation Folin  has  described  a  method  (/.  Biol.  Chem.,  1907,  3,  177), 
but  the  subject  is  not  sufficiently  important  to  justify  a  description 
detailed  enough  to  obviate  reference  to  the  original. 

Assay  of  Commercial  Acetone.— The  British  War  Office  speci- 
fication requires  acetone  for  cordite  manufacture  to  be  colourless  and 
absolutely  transparent,  and  when  mixed  with  distilled  water  in  any 
when  evaporated  on  a  boiling  water-bath,  and  its  sp.  gr.  at  i5°/i5° 
proportion  it  must  show  no  turbidity.  It  must  leave  no  residue 
must  not  exceed  0.800.  It  must  also  endure  the  "permanganate 
test"  for  30  minutes.  The  permanganate  test  is  conducted  as  follows: 
100  c.c.  of  the  acetone  is  mixed  with  i  c.c.  of  o.i  %  potassium  per- 
manganate solution,  kept  at  a  temperature  of  15°  and  the  time  ob- 
served for  the  colour  of  the  permanganate  to  disappear.  This 
specification  is  said  to  ensure  the  absence  of  any  impurity  other  than 
a  very  small  quantity  of  ethyl  methyl  ketone.  Since  1904  the  fol- 
owing  clause  has  been  added  to  the  specification: 

uThe  acetone  is  not  to  contain  more  than  0.002  %  of  carbon 
dioxide,  and  is  otherwise  to  be  quite  neutral." 

In  titrating  acetone  with  acid  or  alkali  it  is  well  to  dilute  it  with 
an  equal  bulk  of  recently-boiled  distilled  water.  For  the  estimation 
of  basic  bodies  and  strong  acids  ^-nitrophenol  is  usually  employed 
as  indicator,  while  for  weak  acids  phenolphthalein  is  used  after 
boiling  to  expel  carbon  dioxide.  The  latter  is  estimated  by  titration 
of  the  unboiled  sample,  using  phenolphthalein  as  indicator.  (Mar- 
shall, /.  Soc.  Chem.  Ind.,  1904,  23,  646.) 

In  examining  samples  of  acetone,  less  carefully  fractionated,  the 
following  observations  of  Heikel  (Chem.  Zeit.,  1908,  32,  75)  are  useful. 
The  higher  ketones  react  with  iodine  and  with  mercuric  sulphate,  but 
consume  less  of  the  reagent  per  unit  of  weight  than  does  acetone. 
Thus  the  fraction  known  in  the  trade  as  "ketones"  (mainly  ethyl 
methyl  ketone),  sp.  gr.  0.811  to  0.815,  appears  to  contain  90%  of 
acetone  by  Messenger's  method  and  63.5%  by  that  of  Deniges.  The 
"light  acetone  oil"  of  the  trade,  sp.  gr.  0.82  to  0.83,  appears  to  con- 
tain 57%  of  acetone  by  Messenger's  method  and  only  32.5%  by  that 
of  Deniges.  This  fraction  contains  little  or  no  acetone  really,  but  it 
is  the  apparent  acetone  content  by  the  two  methods  or  the  Deniges- 
Messenger  ratio  which  is  valuable  in  judging  the  sample.  For  acetone 
itself  the  ratio  is  of  course  i,  for  "ketones"  as  the  above  numbers 


IIO  ALCOHOLS. 

show  about  0.7,  and  for  light  oil  about  0.57.  Moreover,  the  mercury 
precipitate  with  "ketones"  is  no  longer  white,  but  yellowish,  while 
that  from  the  light  oils  is  yellowish-brown. 

ETHYL  ALCOHOL. 

Alcohol,  Methyl  Carbinol. 

Pure  ethyl  alcohol  is  a  colourless,  nearly  odourless,  mobile  liquid, 
possessed  of  a  burning  taste.  Its  b.  p.  varies  from  76.36°  at  710  mm. 
to  79.31°  at  790  mm.  (Fuchs,  Zeitsch.  angew.  Chem.,  1898,38,870).  It 
solidifies  at  — 112.3°  (Ladenburg  and  Krugel,  Ber.,  1899,  32,  1818). 
The  sp.  gr.  is  probably  not  far  from  0.79394  at  6o°/6o°  F.,  the  tem- 
perature adopted  for  alcoholometry  in  Britain.  The  numbers  of 
Mendeleef — (Zeitsch.  Chem.,  1865,  260,  and  Ann.  Phys.  Chem.,  1869, 
138,  ii,  138,  103  and  250),  of  Young  (Trans.  Chem.  Soc.,  1902,  81, 
717),  and  of  Klason  and  Norlin  (Arkiv  Kem.  Min.  Geol.,  1906,  2,  No. 
24),  when  calculated  to  6o°/6o°  F.,  become  0.79393,  0.79395  and 
0.79394,  respectively.  Squibb  (Ephemeris,  1884,  2,  522,  and  Pharm. 
J-  (3)7  I5>  22)  nas  obtained  alcohol  of  sp.  gr.  0.79350,  and  there 
is  a  natural  presumption  in  favour  of  the  lowest  recorded  number,  but 
Young's  method  of  preparation  makes  it  unlikely  that  his  number 
is  higher  than  the  truth  and  he  suggests  that  Squibb's  alcohol  con- 
tained ether.  The  tables  of  specific  gravities  of  aqueous  alcohol 
most  commonly  in  use  are  based  on  the  earlier  (1847-8)  work  of 
Fownes  and  Drinkwater,  using  alcohol  of  a  sp.  gr.  of  0.7938,  while 
the  tables  of  Tralles,  which  alcohol  has  a  sp.  gr.  of  0.7946,  are  still 
the  basis  of  the  excise  work  in  Britain.  The  co-efficient  of  expansion 
is  very  large,  a  point  of  considerable  importance  to  the  analyst,  who 
usually  estimates  alcohol  from  the  sp.  gr.  of  its  aqueous  solutions. 

Alcohol  is  miscible  with  water  in  all  proportions,  a  considerable 
evolution  of  heat  and  contraction  in  bulk  taking  place  on  admixture. 

The  presence  of  as  small  a  proportion  as  0.5%  of  water  in  alcohol 
is  indicated  by  the  pink  color  assumed  by  the  liquid  on  introducing  a 
crystal  of  potassium  permanganate.  A  less  delicate  test  consists  in 
agitating  the  alcohol  with  a  little  anhydrous  cupric  sulphate,  when  the 
salt  will  acquire  a  blue  colour  if  a  notable  quantity  of  water  be  present. 

According  to  P.  Yvon  (/.  Pharm.  Chim.,  1897,  7, 100),  calcium  car- 
bide furnishes  a  ready  means  of  determining  whether  alcohol  is  anhy- 
drous or  not.  On  adding  a  pinch  of  the  powder  to  absolute  alcohol, 
no  bubbles  of  gas  are  liberated  and  the  liquid  remains  transparent, 


ETHYL   ALCOHOL.  Ill 

whilst  if  only  a  trace  of  water  is  present  bubbles  of  acetylene  are  liberated 
and  the  liquid  becomes  milky  from  the  formation  of  calcium  hydroxide. 

Rectified  Spirit  of  Wine  is  the  name  given  to  the  most  concen- 
trated alcohol  producible  by  ordinary  distillation.  The  rectified  spirit 
of  the  British  Pharmacopcea  is  described  as  containing  84  %  by  weight 
of  real  alcohol,  and  having  a  sp.  gr.  of  0.838. 

Proof  Spirit  of  the  British  Pharmacopoeia  has  a  sp.  gr.  of  0.920, 
which  corresponds  to  a  strength  of  about  49  %  by  weight  of  real 
alcohol.  The  term  " proof  spirit"  is  very  confusing  to  many  people, 
and  might  with  advantage  be  abandoned.  Of  this  there  is  little 
chance  at  present,  as  it  is  adopted  in  several  Acts  of  Parliament,  and 
is  the  scale  to  which  Sykes'  hydrometer,  used  by  the  Excise,  has 
reference.'  The  Excise  formerly  tested  the  strength  of  spirits  by  pour- 
ing a  certain  amount  on  gunpowder.  A  light  was  then  applied.  If  the 
spirit  was  above  a  certain  strength  ("proof")  the  gunpowder  ulti- 
mately inflamed,  but  if  weaker  the  gunpowder  was  too  much  moistened 
by  the  water  to  be  capable  of  explosion,  and  the  sample  was  said  to  be 
11  under  proof."  By  Act  of  Parliament,  proof  spirit  is  now  defined  to 
be  a  liquid  of  such  density  that,  at  51°  F.,  13  volumes  shall  weigh  the 
same  as  12  volumes  of  water  at  the  same  temperature.  The  "proof 
spirit"  thus  produced  has  a  sp.  gr.  of  0.91984  at  6o°/6o°  F.,  and  con- 
tains, according  to  Fownes,  49.24%  by  weight  of  alcohol  and  50.76  of 
water.  Spirits  weaker  than  the  above  are  described  by  the  Excise  as 
being  so  many  degrees,  or  so  much  %  "under  proof"  (U.P.).  Thus, 
by  the  term  "spirit  of  20%  or  20  degrees,  under  proof,"  is  meant  a 
liquid  containing,  at  60°  F.,  80  volumes  of  proof  spirit  and  20  of 
water.  "Spirit  of  50°  U.P."  contains  equal  volumes  of  proof  spirit 
and  water,  while  pure  water  is  100°  under  proof. 

On  the  other  hand,  spirituous  liquids  stronger  than  proof  spirit  are 
described  according  to  the  number  of  volumes  of  proof  spirit  100 
volumes  would  yield  when  suitably  diluted  with  water.  Thus,  "spirit 
of  50°  O.P."  is  alcohol  of  such  strength  that  100  volumes  at  60°  F., 
when  diluted  with  water  to  150  volumes,  would  be  proof  spirit.1 
Absolute  alcohol  accordingly  is  75  J°  O.P.,  and  contains  175.25%  of 
proof  spirit,  for  100  volumes  when  diluted  with  water  would  yield 
175.25  volumes  of  spirit  at  "proof." 

1  Owing  to  the  contraction  which  occurs  on  mixing  alcohol  with  water,  the  volume  of 
water  which  it  would  be  necessary  to  add  in  this  instance  would  be  considerably  more  than 
50  measures.  Thus,  a  mixture  of  100  volumes  of  absolute  alcohol  with  60  of  water  only 
measures  154  volumes  instead  of  160. 


112  ALCOHOLS. 

The  relationship  of  percentages  of  absolute  alcohol  to  those  of  proof 
spirit  are  explained  below. 

In  the  United  States,  Tralles'  tables  are  legalised,  and  consequently 
the  proportion  of  alcohol  in  spirit  is  usually  stated  in  percentage  by 
volume;  but  a  " proof  spirit"  is  also  recognized  by  the  American 
Excise,  which  is  denned  as  "that  alcoholic  liquor  which  contains  one- 
half  its  volume  of  alcohol  of  a  specific  gravity  of  0.7939  at  60°.  The 
sp.  gr.  of  such  spirit  is  stated  to  be  0.93353  a^  60°  F.,  water  at  its 
maximum  density  being  taken  as  unity.  (This  will  correspond  to  a 
sp.  gr.  of  about  0.9341  if  water  at  60°  F.  be  taken  as  unity,  and  to  a 
content  of  42.7%  by  weight  of  absolute  alcohol.)  Absolute  alcohol 
would  contain  200  %  of  proof  spirit  according  to  the  United  States 
Excise,  instead  of  175.25%  in  the  English  system.1 

The  United  States  Pharmacopoeia  designates  three  forms  of  alcohol: 

Absolute  Alcohol. — At  least  99  %  by  weight  of  ethyl  hydroxide.  Sp.  gr.  at 
15.6°  not  above  0.797;  at  25°  0.789. 

Alcohol. — 91  %  by  weight  or  94  %  by  volume  of  ethyl  hydroxide.  Sp.  gr.  at 
15. 6°  0.820;  at  25°  0.812. 

Diluted  Alcohol. — About  41  %  by  weight  or  48.6  %  by  volume  of  ethyl  hydrox- 
de.  Sp.  gr.  at  15.6°  0937;  at  25°  0.930. 

Examination  of  Commercial  Alcohol. — Ordinary  spirit  of  wine 
is  commonly  assumed  to  consist  of  only  alcohol  and  water.  This, 
however,  is  frequently  far  from  true,  commercial  alcohol  often  con- 
taining distinct  traces  of  higher  homologues,  of  aldehyde  and  acetic 
acid,  of  volatile  oils  and  of  various  fixed  impurities,  both  organic  and 
inorganic.  Methylated  spirit  of  wine  is  an  acknowledged  mixture  of 
ethyl  alcohol  and  wood  spirit.  For  the  detection  of  the  latter  body 
in  alcoholic  liquids  in  which  its  unacknowledged  presence  is  suspected, 
see  Methyl  Alcohol. 

The  other  common  impurities  of  commercial  alcohol  may  be  sought 
for  by  the  methods  given  for  the  analysis  of  potable  spirits. 

Oily  and  Resinous  Matters  may  be  detected  by  diluting  the  spirit 
somewhat  largely,  when  they  are  precipitated  and  impart  a  milky 
appearance  to  the  liquid. 

Aldehyde  imparts  a  peculiar  flavour  to  the  spirit.     When  present  in 

1 "  High  Wines."  This  term  is  applied  in  the  United  States  to  the  commercial  alcohol  o 
high  strength,  the  amount  of  alcohol  being  usually  indicated  U.  S.  proof  gallons.  95  % 
alcohol  is  termed  190°  proof. 

"  Cologne  Spirit "  "  Silent  Spirit."  These  terms  are  much  used  to  designate  strong  alcohol 
that  has  been  freed  from  all  but  very  small  amounts  of  accessory  substances.  It  has  a  very 
faint  odour.  Such  alcohol  is  used  in  manufacture  of  toilet  preparations,  blended  whiskies 
and  imitations  of  many  alcoholic  beverages. — H.  L. 


ETHYL   ALCOHOL.  1 13 

quantity  the  spirit  becomes  brown  when  heated  with  sodium  hydrox- 
ide. A  smaller  quantity  is  detected  by  adding  a  few  drops  of  solu- 
tion of  silver  nitrate  and  exposing  the  liquid  to  a  good  light  for 
twenty-four  hours,  when  the  silver  will  be  reduced  and  deposited  as  a 
black  powder  if  aldehyde  or  other  reducing  agent  be  present.  Traces 
of  aldehyde  are  nearly  always  present  in  commercial  samples  of 
alcohol.  The  British  Pharmacopoeia  directs  the  silver  test  to  be 
made  by  adding  30  fluid  grains  (2  c.c.)  of  N/io  silver  nitrate  to  4 
fluid  ounces  (120  c.c.)  of  the  sample  to  be  tested.  After  exposure  to 
the  light  for  twenty-four  hours  and  decantation  from  the  black  precipi- 
tate, no  further  reduction  of  silver  should  occur  on  repeating  the 
treatment.  A  negative  result  on  adding  more  silver  solution  and 
again  exposing  the  liquid  to  light  proves  the  absence  of  a  greater  pro- 
portion of  reducing  agents  per  pint  (250  c.c.)  of  spirit  than  can  decom- 
pose about  2.5  grains  (0.6  grm.)  of  nitrate  of  silver. 

The  proportion  of  water  present  in  commercial  alcohol  may  be 
deduced  with  accuracy  from  the  sp.  gr.  of  the  liquid  (p.  115). 

Denatured  Alcohol. — Spirit,  suitably  denatured  so  as  to  be  unfit 
for  drinking  purposes,  is  free  from  duty  in  most  countries.  Formerly 
in  Great  Britain  it  was  only  necessary  to  add  to  the  spirit  one-ninth  of 
its  volume  of  partially  purified  wood  naphtha.  The  British  and 
United  States  specifications  with  which  wood  naphtha  intended  for 
methylating  has  to  comply  are  given  in  the  section  on  Methyl  Alcohol. 
Since  spirit  denatured  in  this  way  can  be  deprived  of  its  offensive 
taste  and  odour  without  great  difficulty,  the  British  Board  of  Inland 
Revenue  subsequently  directed  the  further  addition  of  three-eighths 
of  i  %  of  mineral  naphtha.  In  view  of  representations  which 
were  made  to  the  Board  that  British  manufacturers  were  placed 
at  a  disadvantage  as  compared  with  their  foreign  competitors  by  the 
regulations  with  regard  to  the  use  of  duty-free  alcohol  for  industrial 
purposes,  these  regulations  have  been  revised,  with  the  result  that  a 
very  large  number  of  denaturants  are  now  permitted  in  place  of  crude 
wood  naphtha.  In  these  circumstances,  a  method  for  estimating 
crude  benzene  in  alcohol  is  worth  description. 

For  the  estimation  of  crude  benzene  in  alcohol,  Holde  and  Winterfeld 
(Chem.  Zeit.,  1908,  32,  313)  take  100  c.c.  of  the  spirit,  dilute  it  with 
water  so  that  the  alcoholic  strength  is  reduced  to  approximately 
25%  distil,  collect  the  first  10  c.c.  of  the  distillate  in  an  ice-cooled 
pump-flask,  dilute  it  with  10  to  20  c.c.  of  water  and  pour  the  mixture 
Vol.  I.— 8 


1 14  ALCOHOLS. 

into  a  narrow  measuring  cylinder.  About  0.3  c.c.  of  benzenes  remain 
emulsified  in  the  25  c.c.  or  so  of  dilute  alcohol,  but  any  larger  quantity 
forms  a  separate  upper  layer,  the  volume  of  which  is  read  off  and  0.3 
c.c.  added  to  the  reading.  With  quantities  between  0.5  and  5.0% 
the  maximum  error  should  not  exceed  o.i  per  cent. 

Methylated  Finish  is  a  preparation  sold  by  those  who  are  not 
licensed  as  venders  of  methylated  spirit.  It  is  made  by  dissolving  a 
gum-resin  in  methylated  spirit,  and  the  British  Excise  insists  that  the 
proportion  present  shall  not  be  less  than  3  ounces  in  the  gallon. 

Detection  of  Alcohol. — The  mere  detection  of  alcohol -is  seldom 
important  and,  as  a  rule,  it  can  be  estimated  quickly  and  with  con- 
siderable accuracy.  Methods  for  its  detection  in  ether,  chloroform 
and  some  other  liquids  from  which  it  cannot  be  easily  separated  by 
distillation  are  described  in  the  sections  relating  to  those  substances. 

Alcohol  gives  the  iodoform  reaction  (see  detection  of  acetone), 
but  only  on  warming,  preferably  to  about  60°  for  one  minute.  This 
reaction  can  often  be  applied  to  the  detection  of  alcohol,  although  it  is 
given  by  many  other  substances.  Of  these  substances,  some  give  the 
reaction  in  the  cold,  others  only  after  prolonged  warming.  If  an 
aqueous  liquid,  on  being  neutralised  and  once  or  twice  fractionally 
distilled  through  some  simple  head,  yields  a  distillate  which  has  a 
sp.  gr.  notably  less  than  i,  and  which  gives  the  iodoform  reaction, 
but  only  on  warming,  the  presence  of  alcohol  may  be  suspected,  and 
in  many  cases  the  presence  of  any  of  the  other  substances  which 
might  depress  the  sp.  gr.  and  give  the  iodoform  reaction  is  so  improb- 
able that  such  a  distillate  is  practically  a  proof  of  the  presence  of 
alcohol.  There  is  almost  no  limit  to  the  sensitiveness  of  this  test, 
if  the  number  of  distillations  are  increased. 

E.  Merck  (Chem.  Zeit.,  1896,  20,  228)  proposes  the  following  modi- 
fication of  Davy's  test:  Pure  molybdic  acid  is  dissolved  in  warm 
strong  sulphuric  acid,  and  the  resulting  solution  poured  through  the 
liquid  under  examination  in  a  test-tube,  both  being  kept  as  nearly  as 
possible  at  a  temperature  of  60°.  In  presence  of  alcohol  a  blue  ring 
appears  at  the  junction  between  the  two  liquids,  which  is  the  more 
intense  the  larger  the  proportion  of  alcohol  present.  On  shaking, 
the  colour  disappears,  but  by  addition  of  a  further  quantity  of  the 
reagent  it  may  be  reproduced.  The  test  is,  of  course,  not  charac- 
teristic of  alcohol  only,  but  it  will  detect  even  0.02%  of  ethyl  alcohol 
and  0.2%  of  methyl  alcohol  in  aqueous  solution. 


ETHYL   ALCOHOL. 


Estimation  of  Alcohol. — Alcohol  in  admixture  with  wood  spirit, 
chloroform,  ether,  etc.,  may  be  estimated  by  the  methods  described  in 
the  sections  devoted  to  these  substances.  In  by  far  the  greater 
number  of  instances  the  estimation  of  alcohol  is  effected  by  separating 
it  from  fixed  substances  by  distillation,  and  then  ascertaining  the  pro- 
portion of  alcohol  present  in  the  spirituous  liquid  condensed.  This 
is  practically  the 

Estimation  of  Alcohol  in  Mixtures  consisting  essentially  of  Alcohol 
and  Water  only. 

This  is  most  generally  effected  by  ascertaining  the  sp.  gr.  of  the 
mixture.  From  the  sp.  gr.  at  60°  F.  compared  with  water  at  60°  F., 
the  percentage  of  real  alcohol  is  readily  ascertained  by  reference  to 
tables,  on  the  construction  of  which  great  care  has  been  bestowed 
by  various  observers,  the  subject  being  of  great  importance  for  excise 
purposes.  By  the  excise,  a  glass  or  metal  hydrometer  is  employed, 
the  temperature  of  the  liquid  being  carefully  noted.  In  the  laboratory, 
the  specific -gravity  bottle  is  a  more  satisfactory  and  accurate  instru- 
ment. A  bottle  holding  50  c.c.  is  of  suitable  capacity  for  general  use, 
but  for  some  purposes  a  smaller  one  or  a  loc.c.  Sprengel  tube  will  be 
found  serviceable.  (See  page  5.) 

The  proportion  of  alcohol  contained  in  spirituous  liquids  is  expressed 
in  three  ways:  i.  Percentage  of  alcohol  by  weight.  2.  Percentage 
of  alcohol  by  volume.  3.  Percentage  of  proof  spirit.  Of  these,  the 
first,  in  the  opinion  of  the  author,  is  the  most  satisfactory,  but  both  the 
other  plans  serve  for  certain  purposes.  It  is  convenient  in  some  cases 
to  know  the  weight  of  alcohol  in  100  measures  of  the  spirituous  liquid. 
The  term  " proof  spirit"  has  already  been  explained. 

In  the  following  table  are  given  the  percentages  of  absolute  alcohol 
by  weight  and  of  proof  spirit  by  volume,  which  are  contained  in  mix- 
tures of  alcohol  and  water  of  different  sp.  gr.: 

SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH  WATER. 


Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight 

Percentage 
of  Proof 
Spirit  by 
Measure 

Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight 

Percentage 
of  Proof 
Spirit  by 
Measure 

.79384 

•794 

6 
7 

100.00 

99-94 
.61 

98-97 

175.25 

175.18 
I74-83 
•49 
-14 

.798 

.800 

i 

2 

98.66 

•34 
•°3 
97.70 

•37 

173.81 

•47 
.14 
172.77 
39 

n6 


ALCOHOLS. 


SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.— Continued. 


Specific 
Gravity    at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

Specific 
Gravity    at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

.803 

97  -03 

172.02 

.850 

79-32 

148.84 

4 

96.70 

171.64 

i 

78.92 

.27 

5 

•37 

.26 

2 

•52 

147.69 

6 

•°3  . 

170.88 

3 

.12 

.11 

7 

95-68 

.46 

4 

77.71 

146.51 

8 

•32 

•°3 

5 

.29 

145-89 

9 

94-97 

169.61 

6 

76.88 

.28 

.810 

.62 

.20 

7 

.46 

144.66 

i 

.28 

168.79 

8 

.04 

.04 

2 

93.92 

•38 

9 

75-59 

143-35 

3 

•55 

167.92 

.860 

.14 

142.66 

4 

.18 

.46 

i 

74.68 

141.96 

5 

92.81 

.OO 

2 

•23 

.26 

6 

•44 

I66.53 

3 

73-79 

140.59 

7 

.07 

.07 

4 

•38 

139.96 

8 

•7i 

165.62 

5 

72.96 

•32 

9 

91.36 

.18 

6 

.S2 

138-65 

.820 

.00 

164.74 

7 

.09 

I37.98 

i 

90.64 

.29 

8 

71.67 

•33 

2 

.29 

163.84 

9 

•25 

136.69 

3 

89.92 

•38 

.870 

70.84 

.07 

4 

•54 

162.88 

i 

•44 

135-45 

5 

.16 

.38 

2 

.04 

134.84 

6 

88.76 

I6I.86 

3 

69.63 

.19 

7 

.36 

•32 

4 

.21 

!33-54 

8 

87.96 

160.79 

5 

68.79 

132.89 

9 

•58 

.28 

6 

•38 

•23 

.830 

.19 

159-77 

7 

67.96 

131-58 

i 

86.81 

.26 

8 

•54 

130.92 

2 

.42 

158.74 

9 

.J3 

.26 

3 

.04 

•23 

.880 

66.70 

I29-57 

4 

85-65 

157.71 

i 

.26 

128.87 

5 

.27 

.19 

2 

65-83 

.19 

6 

84.88 

156.66 

3 

•42 

127.52 

.      7 

.48 

.10 

4 

65.00 

126.85 

8 

.08 

155-55 

5 

64.57 

•15 

.8382 

84.00* 

•45 

6 

•«3 

125.44 

•839 

83.69 

.02 

7 

63.70 

124-73 

.840 

•31 

154-49 

8 

.26 

.02 

i 

82.92 

I53-96 

9 

62.82 

123.29 

2 

•54 

.43 

.890 

-36 

122.53 

3 

•*5 

152.89 

i 

61  .92 

121.79 

4 

81.76 

•34 

2 

•5° 

.11 

5 

•36 

151.78 

3 

.08 

120.42 

6 

80.96 

.21 

4 

60.67 

119.74 

7 

•54 

I50.6I 

5 

.26 

•05 

8 

•13 

.00 

6 

59-83 

118.34 

9 

79.72 

149.38 

7 

•39 

II7.6l 

*  Rectified  Spirit  B.  P. 


ETHYL   ALCOHOL. 


SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.— Continued. 


Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

Specific 
Gravity    at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

.898 

58.95 

116.88 

-933° 

43-24 

89.06 

9 

•5° 

.11 

35 

.00 

88.62 

.900 

•°5 

"5-33 

40 

42.76 

.18 

i 

57-63 

114.62 

45 

•52 

87-73 

2 

.21 

113.92 

50 

.29 

.29 

3 

56.77 

.18 

55 

•°5 

86.84 

4 

•32 

112.41 

60 

41.80 

•37 

5 

55-86 

in  .64 

65 

•55 

85.90 

6 

.41 

110.84 

70 

•3° 

•43 

7 

54-95 

•°3 

75 

•°5 

84.96 

8 

.48 

109.20 

80 

40.80 

•  49 

9 

.00 

108.36 

85 

•55 

.02 

.910 

53-57 

107.61 

90 

•3° 

83.54 

i 

•!3 

106.86 

95 

•05 

.07 

2 

52.68 

.07 

.9400 

39-8o 

82.59 

3 

•23 

105.27 

°5 

•55 

.12 

4 

51-79 

104.50 

10 

•3° 

81.64 

5 

-38 

103.78 

15 

•°5 

•!7 

6 

50.96 

•°5 

20 

38.78 

80.64 

7 

•52 

102.28 

25 

•5° 

.11 

8 

.09 

101  .51 

30 

.22 

79-57 

9 

49-64 

100.68 

35 

37-94 

.04 

.91984 

49.24* 

IOO.OO 

40 

•67 

78.50 

.9200 

.16 

99.86 

45 

•39 

77.96 

05 

48.96 

•  49 

5° 

.11 

.42 

10 

•73 

.08 

55 

36.83 

76.88 

15 

•5° 

98.67 

60 

•56 

-34 

20 

.27 

.26 

65 

.28 

75.80 

25 

•°5 

97-85 

70 

.00 

.26 

30 

47.82 

.44 

75 

35-75 

74.78 

35 

•59 

•°3 

80 

•5° 

-3° 

40 

-36 

96.62 

85 

•25 

73-8i 

45 

.14 

.21 

90 

.00 

•33 

5° 

46.91 

95-79 

95 

34.76 

72.87 

55 

.68 

•38 

.9500 

•52 

•  4i 

60 

-46 

94-97 

°5 

.29 

7J-94 

65 

-23 

•55 

10 

•05 

.48 

70 

.00 

.14 

15 

33-76 

70.92 

11 

45-77 
-55 

93-73 
•31 

20 
25 

•47 
.18 

•34 
69-76 

85 

•32 

92.89 

30 

32-87 

.16 

90 

.09 

.48 

35 

•56 

68.54 

95 

44.86 

.06 

40 

•25 

67.92 

.9300 

.64 

91.64 

45 

31.94 

•3° 

05 

.41 

•23 

50 

.62 

66.68 

10 

.18 

90.81 

55 

•3i 

•05 

15 

43-95 

•39 

60 

.00 

65-43 

20 

•7i 

89-95 

65 

30.72 

64.87 

25 

-48 

•5° 

70 

•44 

•32 

*  Proof  Spirit. 


u8 


ALCOHOLS. 


SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.— Continued. 


Specific 
Gravity    at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

Specific 
Gravity    at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

•9575 

30.17 

63.77 

.9684 

22.54 

48.19 

80 

29.87 

.17 

5 

.46 

•03 

85 

53 

62.49 

6 

•38 

47-87 

90 

.20 

61.82 

7 

•71 

95 

28.87 

.16 

8 

•23 

•55 

.9600 

•56 

60.53 

9 

•15 

•39 

05 

•25 

59-90 

.9690 

.08 

•23 

10 

27-93 

.26 

i 

.00 

•07 

15 

•57 

58.53 

2 

21  .91 

46.92 

20 

.21 

57.80 

3 

•85 

.76 

25 

26.87 

.09 

4 

•77 

•59 

3° 

•53 

56.41 

5 

.69 

•43 

35 

.20 

55-73 

6 

.62 

.27 

40 

25.86 

-03 

7 

•54 

.11 

45 

•5°               54-3° 

8 

.46 

45-95 

.9650 

.14 

53-56 

9 

•38 

•79 

i 

.07 

.42 

.9700 

•31 

•63 

2 

.00 

•27 

i 

•23 

•47 

3 

24.92                    .11 

2 

•15 

•31 

4 

•85               52.95 

3 

.08 

•15 

5 

•77 

.80 

4 

.00 

44-99 

6 

.69 

.64 

5 

20.91 

.81 

7 

.62 

.48 

6 

'      -83 

-63 

8 

•54 

•32 

7 

•75 

.46 

9 

.46 

.16 

8 

.66 

•29 

.9660 

•38 

.00 

9 

•58 

.12 

i 

51.84 

.9710 

•50 

43-94 

2 

•23 

.69 

i 

•  42 

•77 

3 
4 

3 

•53 
•37 

2 

3 

•33 
•25 

.60 
•42 

5 

.00 

.21 

4 

•  I7 

•25 

6 

23.92 

.05 

5 

.08 

7 

•85 

50.89 

6 

.00 

42.90 

8 

•77 

•73 

7 

19.91 

•73 

9 

.69 

•57 

8 

•83 

•55 

.9670 

.62 

.41 

9 

•75 

•38 

i 

•54 

•25 

.9720 

.66 

.20 

2 

.46 

.10 

i 

•58 

.03 

3 

•38 

49-94 

2 

•So 

41.85 

4 

•78 

3 

•  42 

.68 

5 

•23 

•63 

4 

•33 

.51 

6 

•  J5 

•47 

5 

•25 

•33 

7 

.08 

•3i 

6 

•17 

41.16 

8 

.00 

7 

.08 

40.98 

9 

22.91 

48.99 

8 

.00 

.81 

.9680 

•85 

•83 

9 

18.92 

.64 

i 

•77 

•67 

•9730 

.85                    .48 

2 

.69 

.51 

i 

•77                   -32 

3 

.62 

•35 

2 

.69                   .16 

ETHYL   ALCOHOL. 


SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.—  Continued. 


Specific 
Gravity    at 
6o°/6o°  F. 

,   Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

Snerifir        Percentage       Percentage 
of  Absolute        of  Proof 

vJId-Vlly    3,1                AI        i_     i                    o     •    •      i 

6o°/6o°  F          Alcohol            Spirit  by 
by  Weight.        Measure. 

•9733 

18.62 

40.00 

•9783 

14.50 

31-41 

4 

•54 

39-83 

4 

•42 

.22 

5 

.46 

-67 

5 

•33 

•°3 

6 

•38 

6 

•25 

30.84 

7 

.31 

•35 

7                    •I7 

.64 

8 

•23 

.19 

8                    .08 

•45 

9 

.03        |            9                    .00 

.26 

.9740 

i 

!o8 
.00 

38.87 
•71 

.9790                13.92 
i                    -85 

.10 
29-93 

2 

17.91 

•53 

2 

•77 

•77 

3 

•83 

•36 

3 

.69 

.61 

4 

•75 

.18 

4 

.62 

•  44 

5 

.66 

.01 

5 

•54 

.29 

6 

•58 

37-83 

6 

•46 

.11 

7 

•5° 

.66 

7 

•39 

28.95 

8 

.42 

•  48 

8                    .31 

•79 

9 

.  -33 

.31 

9                    -23 

.62 

•975° 

•25 

•13 

.9800                    .15 

.46 

i 

36.96 

i                    .08 

.29 

2 

.08 

•78 

2                              .00 

•13 

3 

.00 

.61 

3                12.92                27.97 

4 

16.91 

•43 

4                     .85                     .80 

5 

•83 

.27 

7                     -77                    -64 

6 

•75 

.11 

6                     .69                    .48 

7 

.66 

35-95 

7 

.62                   .31 

8 

•58 

•77 

8 

•54                  -15 

9 

•5° 

.62. 

9                    .46               26.98 

.9760 

•  42 

•46 

.9810                    .39                   .82 

i 

•33 

•30 

i                     .31                    .66 

2 

•25 

•  14 

2                               .23                               .49 

3 

•  J7 

34-97 

3                    -15 

•33 

4 

.08 

.82 

4                     .08 

.16 

5 

.00 

.66 

5 

.00 

.00 

6 

15.91 

•5° 

6 

ii  .92 

25-83 

7 

.     -83 

•32 

7 

'  -85 

.66 

8 

•75 

.14 

8 

•77 

•5° 

9 

.66 

33  -96 

9 

.69 

•34 

.9770 

-58 

•78 

.9820                    .62 

•17 

i 

•5° 

.61 

i                    -54 

.01 

2 

.42 

.43                      2                     .46 

24.84 

3 

•33 

.26 

3                    -39                   -68 

4 

•25 

.08 

4                    -31 

•52 

5 

32.91 

5                    -23 

•36 

6 

!o8 

•73 

6                    .15 

.20 

7 

.00 

•56 

7                   .08                   .04 

8 

14.91 

.38                                         .00               23.87 

9 

•83 

.18                     9                10.91                    .67 

.9780 

•75 

31.99              .9830                     .81 

•47 

i 

.66 

•79 

i                   .72                   .27 

2 

•58 

.60 

2 

•63 

.07 

I2O 


ALCOHOLS. 


SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.— Continued. 


Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

! 

i    Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

.9833 

10.54 

22.87 

.9882 

6-95 

15.16 

4 

•44 

.67 

3 

.89 

•03 

5 

•35 

•47 

4 

.82 

14.88 

6 

.26 

.27 

5 

•75 

•73 

7 

.16 

.07 

6 

.69 

.60 

8 

.07 

21.87 

7 

.62 

•45 

9 

9-99 

.70 

8 

•55 

•3° 

.9840 

.92 

•55 

9 

•  49 

•I7 

i 

.85 

.40 

.9890 

.42 

.02 

2 

.78 

•25 

i 

•35 

I3.87 

3 

.70 

.08 

2 

.29 

•74 

4 

•63 

20.93 

3 

.22 

•59 

5 

•56 

.78 

4 

•15 

•43 

6 

.49 

•63 

5 

.09 

•3° 

7 

.41 

•46 

6 

.02 

•15 

8 

•34 

•3i 

7 

5.96 

.02 

9 

.27 

.16 

8 

•85 

12.87 

.9850 

.20 

.01 

9 

•83 

•74 

i 

.12 

19.84 

.9900 

•77 

.61 

2 

•°5 

.69 

i 

.70 

.46 

3 

8.98 

•54 

2 

•  64 

•33 

4 

.91 

•38 

3 

•58 

.20 

5 

.84 

•23 

4 

•5i 

•05 

6 

•77 

.08 

5 

•45 

II  .92 

7 

.70 

18.93 

6 

•39 

•79 

8 

.62 

.76 

.       7 

•32 

.64 

9 
.9860 

3 

.61 
•  46 

8 
9 

.26 

.20 

•Si 
•38 

i 

.41 

•3i 

.9910 

•13 

.22 

2 

•34 

.16 

i 

.07 

.09 

3 

.27 

.01 

2 

.01 

10.96 

4 

.20 

17.86 

3 

4.94 

.81 

5 

•13 

•71 

4 

.88 

.68 

6 

.06 

.56 

5 

.82 

•55 

7 

7-99 

.41 

6 

.76" 

.42 

8 

.92 

.26 

7 

.70 

.29 

9 

•85 

.10 

8 

.64 

.16 

.9870 

.78 

16.95 

9 

•57 

.01 

i 

•7i 

.80 

.9920 

•5i 

9.88 

2 

.64 

•65 

i 

'•45 

•75 

3 

•57 

•50 

2 

•39 

.62 

4 

•5° 

•35: 

3 

•33 

•49 

5 

•43 

.20 

4 

•27 

•36 

6 

•37 

.07 

5 

.20 

.20 

7 

•3° 

15.92 

6 

.14 

.07 

8 

•23 

•77 

7 

.08 

8.94 

9 

.16 

.62 

8 

.02 

.81 

.9880 

.09 

•47 

9 

3.96 

.68 

i 

.02 

•31 

•9930 

.90 

•55 

ETHYL   ALCOHOL. 

SPECIFIC  GRAVITIES  OF  MIXTURES  OF  ALCOHOL  WITH 
WATER.— Continued. 


121 


Specific 
Gravity  at 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure 

Specific 
Gravity  of 
6o°/6o°  F. 

Percentage 
of  Absolute 
Alcohol 
by  Weight. 

Percentage 
of  Proof 
Spirit  by 
Measure. 

•9931 

3.84                 8  42             .9966 

1.83 

4-03 

2 

.78 

.29                     7 

•78 

3-92 

3 

•73 

.18 

8 

•73 

.81 

4 

.67 

•05 

9 

.67 

.68 

5 

.61 

7.92 

.9970 

.61 

•54 

6 

•55 

•79 

i 

•56 

•43 

7 

.49 

.66 

2 

•Si 

•32 

8 

•43 

•53 

3 

•45 

.19 

9 

•37 

.40 

4 

.40 

.08. 

.9940 

•32 

.29 

5 

•34 

2-95 

i 

.26 

.16 

6 

•29 

.84 

2 

3 

.20 

.14 

.02 
6.89 

1 

:3 

.60 

4 

.08 

.76 

9 

.12 

•47 

5 

.02 

•63 

.9980 

.07 

•36 

6 

2-97 

•52 

i 

.02 

•25 

7 

.91 

39 

2 

0.96 

.12 

8 

•85 

.26 

3 

.91 

.OI 

9 

•79 

.13 

4 

•85 

1.87 

•995° 

•74 

.02 

5 

.80 

.76 

i 

.68 

5-89 

6 

•74 

•63 

2 

.62 

.76 

7 

.69 

•52 

3 

•57 

•65 

8 

•64 

.41 

4 

•52 

9 

•58 

.28 

5 

•45 

•39 

.9990 

•53 

•17 

6 

•39 

•25 

i 

•47 

.04 

7 

•34 

.14 

2 

.42 

°-93 

8 

.28 

.01 

3 

•37 

.82 

9 

.22 

4.88 

4 

•32 

.71 

.9960 

•17 

5 

.26 

•57 

i 

.11 

.64 

6 

.21 

.46 

2 

•05 

•5i 

7 

.16 

•35 

3 

1.99 

•38 

8 

.11 

.24 

4 

.94 

.27 

9 

•°5 

.11 

5 

•89 

.16 

i  .0000 

.00 

.00 

In  the  part  of  the  foregoing  table  referring  to  alcohol  of  greater 
strength  than  proof  spirit,  only  the  percentages  of  alcohol  and  proof 
spirit  are  given  which  correspond  with  sp.  gr.  which  can  be  accurately 
expressed  by  three  figures.  Between  the  concentrations  of  49  and 
25%  of  absolute  alcohol  the  table  is  more  extended,  and  for  still  more 
dilute  spirit  the  percentages  of  alcohol  and  proof  spirit  are  given 
which  correspond  with  every  degree  of  sp.  gr.  expressed  to  the  fourth 
place  of  decimals.  As  arranged,  the  table  will  be  found  sufficiently 


122  ALCOHOLS. 

copious  for  all  cases  likely  to  occur  in  practice.  When  it  is  desired 
to  ascertain,  in  strong  spirit,  the  proportion  of  alcohol  corresponding 
with  a  figure  of  sp.  gr.  to  the  fourth  decimal  place,  it  may  be  effected 
by  interpolation.  The  following  example  shows  the  application  of 
the  method  to  a  sample  of  spirit  of  0.8673  SP-  gr-  72.09  — 71. 67  =  42; 

and: -  =  .126;  and  72.09  —  .126  =  71. 96,as  the  percentage  of  alcohol 

10 

in  spirit  of  0.8673. 

Some  forms  of  pyknometer  can  be  filled  at  one  temperature  and 
weighed  after  an  interval  at  another,  but  the  ordinary  specific -gravity 
bottle  with  bored  stopper  must  be  weighed  immediately  it  is  filled  and 
consequently  at  the  temperature  of  filling.  When,  as  sometimes 
happens  in  a  chemical  laboratory,  the  dew-point  is  above  60°  F.,  the 
ordinary  specific-gravity  bottle  must  be  abandoned  or  the  comparison 
made  at  a  higher  temperature,  62°  F.  or  64°  F.  or  even  higher,  and, 
apart  from  considerations  of  dew,  it  is  frequently  difficult,  if  not  ac- 
tually impossible,  to  cool  liquids  to  60°  F.  Specific  gravities  are  con- 
.  sequently  determined  at  temperatures  higher  than  60°  F.,  and,  since 
the  coefficient  of  expansion  of  alcohol  is  much  greater  than  that  of 
water,  the  sp.  gr.  at  62°/62°  is  widely  different  from  the  sp.  gr.  at 
6o°/6o°,  and  a  correction  must  be  made.  Liverseege  (Analyst,  1897, 
22,  153)  has  worked  out  a  table  of  corrections  which  represents  the 
mean  of  the  results  of  several  workers,  who  differ  slightly  in  their 
recommendations.  His  table,  however,  shows  the  amount  to  be  added 
to  the  observed  sp.  gr.  supposing  that  this  has  been  determined  at 
T°/6o°,  where  T°  is  some  temperature  higher  than  60°.  It  is  reason- 
able to  suppose  that  any  chemist  will  determine  the  water-content  of 
his  bottle  daily,  and  that  this  weighing  will  be  made  at  the  same  tem- 
perature as  that  of  the  aqueous  alcohol,  and  on  this  supposition  the 
following  table  has  been  constructed.  It  shows  the  amount  to  be 
added  to  the  observed  sp.  gr.  at  6i°/6i°  in  order  to  convert  this  into 
the  sp.  gr.  at  6o°/6o°.  If  the  sp.  gr.  has  been  taken  at  62°/62°, 
double  the  amounts  shown  in  the  table  must  be  added  to  arrive  at  the 
sp.  gr.  at  6o°/6o°,  and  so  on  within  reason,  but  since  alcohol  expands 
unequally  with  equal  increments  of  temperature,  the  correction  is  less 
accurate  when  applied  to  temperatures  far  removed  from  60°,  and  in 
all  alcoholometric  work  it  is  well  to  keep  as  near  to  60°  F.  as  possible. 


ETHYL   ALCOHOL. 


I23 


ADDITIONS  TO  BE  MADE  TO  SPECIFIC  GRAVITIES  OF  AQUEOUS 

ALCOHOL  OBSERVED  AT  6i°/6i°  F. 
In  Order  to  Convert  them  into  Specific  Gravities  at  6o°/6o°  F. 


Addition. 


Op.   gl.   itL  UJ.    /Ul       r  .                   .TVUUU1U11.                    op.   gi.   ill   Ul    /Ul      -T  . 

rvuuiuon. 

0.794  to  0.860 

.00039 

0.963  to  0.964 

.00019 

0.860  to  0.890                  .00038 

0.964  to  0.966 

.00018 

0.890  to  0.905                  -00037 

0.966  to  0.967 

.00017 

0.905  to  0.916                  .00036 

0.967  to  0.968 

.00016 

0.916  to  0.925 

.00035 

0.968  to  0.969 

.00015 

0.925  to  0.932 

.00034 

0.969  to  0.970 

.00014 

0.932100.937                         -00033 

0.970  to  0.971 

.00013 

0.937100.941                         .00032 

0.971  to  0.972 

.00012 

0.941  to  0.944 

.00031 

0.972  to  0.973 

.0001  I 

0.944  to  0.947 

.00030 

0.973  to  0.974 

.00010 

0.947  to  0.949 

.  00029 

'  0.974  to  0.975 

.00009 

0.949  to  0.951 

.  00028 

0.975  to  0.976 

.00008 

0.951  to  0.953 

.  00027 

0.976  to  0.977 

.00007 

0.953  to  0.954 

.  00026 

0.977  to  0.979 

.00006 

0.954  to  0.956 

.00025 

0.979  to  0.981 

.00005 

0.956  to  0.958 

.00024 

0.981  to  0.982 

.00004 

0.958  to  0.959 

.  00023 

0.982  to  0.984 

.00003 

0.959  to  0.961 

.00022 

o  .  984  to  o  .  986 

.00002 

0.961  to  0.962 

.00021 

0.986  to  0.994 

.00001 

0.962  to  0.963 

.  OOO2O 

» 

The  following  rules  give  the  means  of  calculating  percentages  of 
alcohol  by  weight  or  volume  to  the  corresponding  percentages  of  proof 
spirit,  and  vice  versa.  The  percentage  of  alcohol  by  volume  is  a  mode 
of  expression  not  common  in  England,  but  is  the  usual  way  of  valuing 
spirit  adopted  in  France,  Belgium,  Germany,  the  United  States  and 
some  other  countries. 

The  percentage  by  volume  of  absolute  alcohol  may  be  obtained  by 
multiplying  the  percentage  of  proof  spirit  by  the  factor  0.5706. 

The  percentage  by  volume  of  absolute  alcohol  may  also  be  obtained 
by  multiplying  the  percentage  of  alcohol  by  wreight  by  the  observed 
sp.  gr.,  and  dividing  the  product  by  0.7938  (or  multiplying  it  by  1.26). 

The  percentage  by  volume  of  proof  spirit  can  be  obtained  by  dividing 
the  percentage  of  absolute  alcohol  by  volume  by  0.5706  (or  multiplying 
it  by  1.7525). 

The  percentage  by  volume  of  proof  spirit  may  be  obtained  by  multi- 
plying the  percenlage  by  weight  of  absolute  alcohol  by  the  sp.  gr., 
and  the  product  by  2.208. 

The  percentage  of  absolute  alcohol  by  weight  may  be  found  by  divid- 


124  ALCOHOLS. 

ing  the  percentage  of  proof  spirit  by  the  product  of  the  sp.  gr.  and 
2.208. 

The  percentage  of  absolute  alcohol  by  weight  may  be  found  by  multi- 
plying the  percentage  of  alcohol  by  volume  by  0.7938  and  dividing  the 
product  by  the  sp.  gr. 

If  the  percentage  of  alcohol  by  weight  be  called  W,  the  percentage 
by  volume  V,  the  percentage  of  proof  spirit  P,  and  the  sp.  gr.  D,  then 
the  following  equations  embody  the  instructions  given  in  the  fore- 
going rules: 

V  =PXo.57o6. 


V  =-        -  =  WDXi.26. 

0.7938 

P  =—¥—  =  VXi.75?5- 
0.5706 

P  =WDX2.2o8. 

w.     p 


DX2.208 

w  _  VXo.7938 
D. 

The  following  are  examples  of  calculations,  such  as  have  frequently 
to  be  made: 

If  it  be  required  to  know  what  percentage  of  gin  at  20°  U.P.  is  con- 
tained in  a  watered  sample  of  44°  U.P.,  the  following  calculation  will 
suffice: 

(100—44)100       56  X  ioo 

-  =  —          -  =  70  %  by  volume.     Hence  the  sample 

100—20  80 

is  of  a  strength  corresponding  to  the  dilution  of  7  gallons  of  gin  at  20° 
U.P.  to  10  gallons  by  addition  of  water. 

Again,  to  ascertain  the  proportion  of  water  which  must  be  added  to 
spirit  at  35°  O.P.,  to  reduce  the  strength  to  10°  U.  P.: 

(IOO~IO)IO°  =  9°  X  I0°  =  66.7.     That  is,  to  obtain  spirit  of  10° 
ioo-v-35  135 

U.P.  66.7  measures  of  spirit  at  35°  O.P.  must  be  diluted  to  ioo,  or  every 
two  gallons  must  be  made  up  to  three  by  addition  of  water. 

The  estimation  of  alcohol  in  presence  of  fixed  matters  is  usually 
effected  by  distillation  of  the  sample  and  ascertaining  of  the  sp.  gr.  of 
the  distillate.  It  is  sometimes  necessary,  and  generally  advisable,  to 


ETHYL   ALCOHOL.  125. 

neutralise  the  liquid  before  distillation,  but  this  must  not  be  done 
when  ascertaining  the  original  gravity  of  beers. 

The  quantity  to  be  taken  will  depend  on  the  alcoholic  strength 
of  the  sample,  and  is  sometimes  conditioned  by  the  small  quantity 
supplied  to  the  analyst.  100  c.c.  is  a  convenient  quantity  of  beer  or 
wine.  The  beer  should  be  distilled  till  about  80  c.c.  has  come  over, 
and  the  distillate  should  be  made  up  with  distilled  water  to  100  c.c. 
In  the  case  of  wines,  it  is  better  to  add  50  c.c.  of  water  and  a  little 
tannin  to  100  c.c.  of  the  wine,  and  to  distil  until  nearly  100  c.c.  has  been 
collected.  Of  potable  spirits,  which  contain  about  50  %  of  alcohol,  it 
is  convenient,  to  mix  50  c.c.  \vith  100  c.c.  of  water  and  to  distil  over 
about  100  c.c.  Stronger  spirit  should  be  still  further  diluted,  25  c.c. 
being  diluted  to  150  c.c.  with  water,  and  100  c.c.  distilled.  The 
distillate  is  in  any  case  made  up  to  100  c.c.  and  its  sp.  gr.  determined 
at  6o°/6o°  F.  Reference  to  the  tables  will  at  once  show  the  percentage 
of  alcohol  by  weight  contained  in  the  distillate.  Then — 

Sp.  gr.  of  distillate  X  measure  of  distillate  in  c.c.  X  %of  alcohol  found  in  distillate  by  table- 

Sp.  gr.  of  sample  X  measure  of  sample  taken  in  c.c. 
=  Percentage  of  absolute  alcohol  by  weight  contained  in  the  sample. 

This  calculation  involves  the  necessity  of  knowing  the  sp.  gr.  of  the 
original  sample.  If  unknown,  the  50  or  100  c.c.  taken  for  the  experi- 
ment may  be  accurately  weighed,  and  this  weight  in  grams  substituted 
for  the  denominator  of  the  above  fraction. 

The  calculation  can  be  wholly  avoided,  and  a  more  satisfactory 
result  obtained  by  weighing  the  original  sample  instead  of  measuring  it,, 
and  also  weighing  the  distillate.  Then — 

Weight  of  distillate  X  percentage  of  alcohol  found  in  distillate  by  table 

Weight  of  sample  taken 
=  Percentage  of  absolute  alcohol  by  weight  contained  in  the  sample. 

The  following  indirect  method  is  less  accurate  than  the  distillation 
method,  but  is  sometimes  useful.  The  sp.  gr.  of  the  original  liquid  is 
first  taken,  and  then  100  c.c.  is  evaporated  to  expel  alcohol  and  sub- 
sequently made  up  again  with  distilled  water  to  100  c.c.  at  60°  F., 
and  the  sp.  gr.  of  the  alcohol-free  liquid  determined.  Let  this  be  S2 
and  the  sp.  gr.  of  the  original  liquid  5t.  From  these  numbers  it  is 
possible  to  calculate  with  fair  accuracy  what  would  have  been  the  sp. 
gr.,  S,  of  the  distillate,  supposing  the  liquid  had  been  distilled  and  the 
distillate  made  up  to  100  c.c.,  as  follows: 

S  =  r  +  SS. 


126  ALCOHOLS. 

From  the  value  of  6"  thus  found,  the  percentage  of  alcohol  may  be 
found  by  reference  to  the  tables  already  given. 

The  alcoholic  strength  of  potable  spirits,  which,  with  the  exception 
of  gin,  rarely  contain  more  than  0.5%  of  solid  matter,  may  be  ap- 
proximately ascertained  from  the  sp.  gr.  of  the  original  spirit  and 
the  proportion  of  solid  matter.  If  the  spirit  has  a  sp.  gr.,^,  and 
contains  W  grm.  of  solid  matter  per  100  c.c.,  then — 

8  =  8!  —  0.0055W, 

where  5  has  the  same  significance  as  in  the  last  paragraph. 

The  rejractometer  may  be  applied  to  the  estimation  of  alcohol  in 
liquids  consisting  solely  of  alcohol  and  water.  In  the  presence  of 
fixed  matters,  resort  must  be  had  to  distillation,  or  to  an  indirect  method 
exactly  analogous  to  the  indirect  sp.  gr.  method.  A  table  for  use 
with  the  Zeiss  immersion  refractometer  has  been  already  given  in 
the  section  on  Methyl  Alcohol.  A  more  extended  one  is  that  of 
Wagner  and  Schultze  (Zeits.  anal.  Chem.,  1907,  46,  508),  and 
Wagner,  who  has  from  time  to  time,  in  the  Chemiker  Zeitung  and 
elsewhere,  published  sections  of  the  table  in  greatly  extended  form, 
with  convenient  temperature  corrections  for  special  purposes,  has 
recently  brought  out  a  book  (Tabellen  zum  Eintauchrejraktometer; 
Carl  Zeiss,  Jena,  1903)  to  which  readers  are  referred  for  further 
information.  The  refractometer  is  particularly  useful  in  estimating 
methyl  and  ethyl  alcohols  in  admixture,  but  for  the  estimation  of  ethyl 
alcohol  in  aqueous  solution  it  is  a  less  accurate  instrument  than  the 
sp.  gr.,  and  if  it  is  desired  to  obtain  results  of  any  value  by  its  means, 
so  much  attention  must  be  paid  to  the  temperature  that  its  use  can 
hardly  be  recommended  on  the  score  of  speed. 

Boiling-point  Method. — The  estimation  of  the  proportion  of  alcohol 
in  a  liquid  may  be  made  by  noting  the  temperature  of  the  vapour  given 
off  from  the  boiling  liquid.  Wiley  has  described  a  form  of  apparatus 
for  this  purpose  (Jour.  Amer.  Chem.  Soc.,  1896,  18,  1063),  which  he 
claims  yields  quite  accurate  results.  It  consists  of  the  flask,  F,  which 
is  closed  by  the  rubber  stopper,  carrying  the  large  thermometer, 
B,  and  a  tube  leading  to  the  condenser,  D.  The  vapours  which  are 
given  off  during  ebullition  are  condensed  in  D  and  return  to  the  flask 
through  the  tube,  as  indicated  in  the  figure,  entering  the  flask  below 
the  surface  of  the  liquid. 

The  flask  is  heated  by  a  gas-lamp  and  is  placed  upon  a  circular  disc 


ETHYL    ALCOHOL. 


I27 


D 


of  asbestos  in  such  a  way  as  to  cover  entirely  the  hole  in  the  centre  of  the 
asbestos  disc,  which  is  a  little  smaller  than  the  bottom  of  the  flask. 
The  whole  apparatus  is  protected  from  external  influences  of  tem- 
perature by  the  glass  cylinder,  E,  which  rests  upon  the  asbestos  disc 
below  and  is  covered  with  a  de- 
tachable stiff  rubber-cloth  disc 
above. 

The  thermometer,  C,  indi- 
cates the  temperature  of  the  air 
between  F  and  E.  The  reading 
of  the  thermometer,  B,  should 
always  be  made  at  a  given  tem- 
perature of  this  surrounding  air. 
The  tube  leading  from  the  con- 
denser, D,  to  the  left  is  made 
long  and  is  left  open  at  its  lower 
extremity  in  order  to  maintain 
atmospheric  pressure  in  F  and 
at  the  same  time  prevent  the 
diffusion  of  the  alcoholic  vapours 
through  D. 

The  flame  of  the  lamp  is  so 
regulated  as  to  bring  the  tem- 
perature indicated  by  the  ther- 
mometer C  to  about  90°  in  ten 
minutes  for  substances  contain- 
ing not  over  5%  of  alcohol. 
After  boiling  for  a  few  minutes, 
the  temperature,  as  indicated  in 
the  thermometer  B,  is  constant, 
and  the  readings  of  the  ther- 
mometer should  be  made  at 

intervals  of  about  half  a  minute  for  ten  minutes.  Some  pieces  of  scrap 
platinum  placed  in  the  flask  will  prevent  bumping  and  secure  a 
more  uniform  evolution  of  vapour.  Slight  variations  due  to  the 
changes  in  temperature  of  the  vapours  are  thus  reduced  to  a  minimum 
effect  upon  the  final  results.  The  apparatus  is  easily  operated,  is 
quickly  charged  and  discharged  and  with  it  at  least  three  assays  of 
alcohol  can  be  made  in  an  hour. 


128.  ALCOHOLS. 

The  thermometer  used  is  the  same  that  is  employed  for  the  indica- 
tion of  freezing-  and  boiling-points  in  the  estimation  of  molecular 
weights.  The  reading  of  the  thermometer  is  arbitrary,  but  the  degrees 
indicated  are  Centigrade.  The  thermometer  is  set  in  the  first  place  by 
putting  the  bulb  in  water  containing  16  grm.  of  common  salt  to  100 
c.c.  when  the  water  is  fully  boiling,  the  excess  of  mercury  is  removed 
from  the  column  in  the  receptacle  at  the  top,  and  then,  on  placing  in 
boiling  water,  the  column  of  mercury  will  be  found  a  little  above  the  5° 
mark.  This  wrill  allow  a  variation  in  all  of  5°  in  the  temperaturer 
and  a  thermometer  thus  set  can  be  used  for  the  estimation  of  per- 
centages of  alcohol  from  i  to  5.5  by  volume.  When  the  liquor  contains 
a  larger  percentage  of  alcohol  than  this,  it  is  advisable  to  dilute  it  until 
it  reaches  the  standard  mentioned. 

In  order  to  avoid  frequent  checking  of  the  thermometer,  rendered 
necessary  by  changes  in  barometric  pressure,  a  second  apparatus, 
made  exactly  like  the  one  described,  is  used,  in  which  water  is  kept 
constantly  boiling.  It  is  only  necessary  in  this  case  to  read  the  two 
thermometers  at  the  same  instant  in  order  to  make  any  necessary 
correction  required  by  changes  in  barometric  pressure. 

While  no  table  showing  the  percentages  of  alcohol  corresponding  to 
any  given  depression  in  the  temperature  of  the  vapour  is  appended,, 
attention  is  called  to  the  fact  that  the  plotted  line  showing  the  variation 
in  depression  of  zero  to  5%  by  volume  of  alcohol  is  practically  straightr 
and  that  for  each  0.8°  change  in  temperature  of  the  vapour  there  is  a 
change  of  about  i  %  by  volume  of  alcohol.  This  rule  can  be  safely 
applied  for  practical  purposes  to  all  liquors  contain  ng  not  more  than 
an  5-5  %  of  alcohol.  For  example,  if,  in  a  given  case,  the  tempera- 
ture of  the  vapour  of  boiling  water,  as  marked  by  the  thermometer, 
is  5.155°  and  the  temperature  of  that  from  a  sample  of  beer  is  2.345°, 
the  depression  is  equivalent  to  2.810,  and  the  percentage  of  alcohol  by 
volume  is,  therefore,  2.81  divided  by  0.80  =  3.51. 

The  thermometer  used  is  graduated  to  hundredths  of  a  degree,  and, 
read  by  means  of  a  cathetometer,  will  easily  give  readings  to  five 
thousandths  of  a  degree. 

The  reading  of  the  thermometer  is  facilitated  by  covering  the  bulb 
with  a  test-tube  containing  water.  The  high  specific  heat  of  the 
water  distributes  evenly  any  little  variations  of  temperature  which 
otherwise  would  cause  the  mercurial  column  in  thermometer  B  to 
oscillate.  The  water  jacket  also  serves  as  a  protection  against  the 


ETHYL   ALCOHOL.  1 29 

projection  of  any  particles  of  the  boiling  liquor  directly  against  the 
bulb  of  the  thermometer. 

Freezing-point  Method. — Alcohol  in  aqueous  solution  can  be 
estimated  with  fair  accuracy  by  observing  the  depression  of  the 
freezing-point  in  Beckmann's  apparatus,  provided  the  alcohol  does 
not  exceed  7%.  Below  that  strength,  the  depression  of  the  freezing- 
point  is  approximately  proportional  to  the  percentage  of  alcohol,  being 
being,  according  to  Gaunt  (Zeit.  anal.  Chem.,  1905,  44, 106),  0.425  for 
each  i  %.  The  method  is  said  by  Gaunt  to  be  quicker  than  the  sp.  gr. 
method. 

Other  methods  for  the  estimation  of  alcohol  have  been  based  on  its 
rate  of  dilatation  by  heat,  on  the  surface-tension  of  the  liquid,  and  on 
the  tension  of  its  vapour.  These  methods  are  capable  of  being  used 
with  advantage  under  special 'circumstances,  but  they  require  special 
apparatus  and  are  generally  less  accurate  and  convenient  than  those 
already  given. 

The  Estimation  of  Alcohol  in  Essences,  Tinctures  and  other 
preparations  containing  substances  volatile  with  alcoholic  steam 
presents  difficulties  that  may  in  most  cases  be  surmounted  by  having 
recourse  to  the  following  method,  due  to  Thorpe  and  Holmes  (Trans. 
Chem.Soc.,  1903,  83,  314): 

"  25  c.c.  of  the  sample,  measured  at  60°  F.,  are  mixed  with  water  in 
a  separator  to  a  bulk  of  from  100  to  150  c.c.,  and  sodium  chloride  is 
added  in  quantity  sufficient  to  saturate  the  liquid.  The  mixture  is  now 
shaken  vigourously  for  5  minutes  with  from  50  to  80  c.c.  of  petroleum 
spirit,  boiling  below  60°  C.,  and  after  standing  for  about  half  an  hour, 
the  lower  layer  is  drawn  off  into  another  separator,  extracted,  if  neces- 
sary, a  second  time  with  petroleum  spirit,  and  then  drawn  off  into  a 
distillation  flask.  Meanwhile  the  layers  of  petroleum  spirit,  are 
washed  successively  writh  25  c.c.  of  saturated  sodium  chloride  solution, 
and  the.  washings  added  to  the  main  bulk,  which  is  neutralised  if 
necessary,  and  then  distilled  and  the  distillate  made  up  to  100  c.c. 

"The  method,  as  described,  is  applicable  to  preparations  containing 
ether,  chloroform,  benzaldehyde  and  esters.  In  the  greater  number  of 
cases,  for  example,  essences  of  lemon,  juniper,  peppermint  and  santal- 
oil  preparations,  a  single  extraction  is  sufficient. 

"In  the  case  of  all  preparations  containing  camphor,  25  c.c.  of 
normal  sulphuric  acid  are  used  instead  of  sodium  chloride,  and  one 
extraction  spirit  is  made.  Before  distilling  it  is  desirable  to  neutralise 
Vol.  I.— o 


130  ALCOHOLS. 

with  sodium  hydroxide,  and  if  the  volume  of  the  liquid  becomes 
inconveniently  large  some  sodium  chloride  is  also  added.  In  pre- 
parations containing  ammonia  this  is  inadmissible,  and  the  liquid  to 
be  distilled  must  be  slightly  acid.1 

The  Estimation  of  Ethyl  Alcohol  in  Fusel  Oil  is  sometimes 
required,  since  fusel  oil  containing  less  than  15  %  of  proof  spirit  is 
admitted  duty  free  into  the  United  Kingdom.  Thorpe  and  Holmes 
have  shown  that  the  method,  above  described,  enables  them  to 
estimate  the  ethyl  alcohol  accurately  in  a  mixture  of  73  alcohol,  20 
fusel  oil  and  7  water.  If  the  proportions  are  8  alcohol,  90  fusel  oil 
and  2  water,  it  may  be  necessary  to  use  rather  more  petroleum  spirit 
and  less  sodium  chloride  solution,  but  otherwise  the  method  is  pre- 
sumably applicable. 

Formerly  fusel  oil  was  tested  by  the  Excise  by  shaking  it  with  an 
equal  volume  of  water  to  remove  the  spirit,  and  then  ascertaining  the 
amount  of  alcohol  contained  in  the  aqueous  liquid  by  taking  its  sp.  gr. 
and  noting  its  volume.  The  test  gives  erroneous  results,  as  fusel  oil 
is  a  mixture  of  alcohols,  of  which  only  amyl  alcohol  is  approximately 
insoluble  in  water.  As  an  improvement  on  this  test,  G.  L.  Ulex 
(Neues  Jahrb.  der  Pharm.,  39,  333)  recommended  the  following, 
based  on  the  low  temperature  at  which  ethyl  alcohol  distils;  100  c.c. 
of  the  sample  are  heated  in  a  retort  until  5  c.c.  have  passed  over;  the 
distillate  is  shaken  with  an  equal  volume  of  a  saturated  solution  of 
sodium  chloride,  and  the  mixture  allowed  to  stand.  If  the  fusel  oil 
which  separates  amounts  to  one-half  of  the  distillate  or  more,  the 

1The  requirement  of  the  U.  S.  (Federal)  food-law  and  of  some  state  food-laws,  that 
medicinal  preparations  must  bear  on  the  label  a  statement  of  the  percentage  of  alcoho, 
present  renders  it  necessary  for  manufacturers  to  verify  the  amount  in  preparations  when 
finally  prepared  for  sale.  C.  E.  Vanderkleed  (Amer.  Jour.  Pharm.  1909,  89,  129)  has  made 
a  special  study  of  this  phase  of  the  problem  and  recommends  the  following  method: 

50  c.c.  of  the  preparation,  measured  at  a  known  temperature,  are  transferred  (in  portions, 
if  necessary)  to  a  test  tube  having  an  inside  diameter  of  22  mm.  and  a  height  of  200  mm., 
marked  at  50  c.c.  The  tube  is  heated  until  in  the  water  bath  all  alcohol  is  driven  off, 
The  liquid  is  cooled  to  the  original  temperature,  and  U.  S.  Pharmacopreia  alcohol  (see  page 
112)  at  the  same  temperature  is  run  in  from  a  burette  until  an  amount  has  been  added  which 
when  diluted  with  water  to  exactly  50  c.c.  would  give  the  same  alcoholic  strength  as  the 
menstruum  that  was  used  in  manufacture  of  the  preparation  being  assayed.  The  tube  is 
stoppered,  the  contents  mixed  and  the  sp.  gr.  ascertained  (Vanderkleed  uses  a  Westphal 
balance).  Subtract  algebraically  the  original  sp.  gr.  from  that  of  the  solution  obtained  in 
the  process,  and  subtract  this  remainder  from  the  theoretical  dilution  above  noted,  and 
ascertain  from  the  standard  tables  the  percentage  of  alcohol. 

Vanderkleed  assayed  fluid  extracts  of  Buchu,  Cubeb  and  Santal  of  known  composition 
and  found  that  the  simple  distillation  method  and  the  method  of  Thorpe  and  Holmes  gave 
lower  results  than  the  above  method.  Inasmuch  as  these  complex  medicinal  preparations 
are  liable  to  furnish  a  distillate  that  contains  other  substances  than  alcohol, Vanderkleed 
does  not  regard  the  refraction  method  as  offering  any  advantage  in  the  solution  of  this 
special  problem. — H.  L. 


ETHYL   ALCOHOL.  13! 

sample  is  sure  to  contain  less  than  15  %  of  spirit,  and  is  free  from 
any  fraudulent  admixture  with  the  same.  If  less  fusel  oil,  or  none 
at  all,  separates,  the  presence  of  15  %  of  the  spirit  may  be  safely  as- 
sumed. In  the  latter  case,  the  quantity  of  the  adulterant  may  be 
ascertained  by  shaking  a  known  measure  of  the  sample  with  an  equal 
bulk  of  a  saturated  solution  of  sodmm  chloride  (in  which  propyl  and 
butyl  alcohols  are  much  less  soluble  than  in  water),  allowing  the 
aqueous  liquid  to  settle  out,  distilling  it,  and  estimating  the  contained 
alcohol  by  noting  the  volume  and  sp.  gr.  of  the  distillate. 

Allen  showed  the  accuracy  of  another  method  of  approximately 
separating  amyl  alcohol  from  ethyl  alcohol,  which  is  to  agitate  the 
sample  in  a  graduated  tube  with  an  equal  volume  of  benzene  or 
petroleum  spirit,  subsequently  adding  sufficient  water  to  cause  the 
benzene  to  separate.  The  increase  in  the  volume  of  the  benzene  in- 
dicates with  approximate  accuracy  the  amount  of  amyl  alcohol  in  the 
sample  under  examination. 

Peters  (Pharm.  Centralh.,  1905,  46,  563)  has  described  a  method, 
similar  to  that  of  Thorpe  and  Holmes,  but  more  complicated.  The 
fusel  oil  is  shaken  with  water  and  petroleum  spirit  and  the  aqueous 
layer  distilled.  The  distillate  is  then  shaken  with  light  petroleum  spirit 
and  calcium  chloride  solution  and  the  aqueous  layer  again  distilled. 


MALT  AND  MALT  LIQUORS. 

BY  JULIAN  L.  BAKER,  F.I.C. 

Malt  is  prepared  by  steeping  barley  or  other  grain  in  water,  and 
allowing  it  to  germinate,  the  sprouted  grain  being  subsequently  dried 
and  cured  in  a  kiln.  During  these  operations  the  composition  of  the 
grain  is  materially  modified.  There  is  a  reduction  in  the  amount  of 
starch  which  has  been  used  up  by  the  growing  embryo  and  an  increase 
in  the  soluble  carbohydrates;  also  a  large  quantity  of  the  insoluble 
nitrogenous  matters  present  in  the  barley  becomes  converted  into  solu- 
ble modifications.  The  following  figures  %  illustrate  the  differences 
between  barley  and  malt  (English). 

BARLEY.  MALT. 

per  cent.  per  cent. 

Moisture 15 2 

Proteins 10 1 1 

Fat 2 o 

Sugar  and  gum  ..n 1 6 

Starch 55 63 

Fiber 5 6 

Ash 2 2 

Well-malted  barley  ranges  in  colour  from  light  to  dark  yellow  accord- 
ing to  the  origin  of  the  barley  and  the  degree  of  curing.  On  breaking 
the  malt  corn  the  interior  should  be  pure  white,  unless  the  drying 
has  been  intentionally  carried  so  far  as  to  partially  caramelise  the  sugar, 
as,  for  example,  with  amber  malts.  It  is  customary  for  the  brewer  or 
maltster  to  form  an  opinion  of  a  sample  of  malt  from  its  crispness  and 
flavour.  Each  corn  should  break  easily  between  the  teeth  and  the  sweet 
characteristic  malty  flavour  should  be  quickly  developed.  If  the  corns 
are  hard  or  steely  it  indicates  that  the  drying  has  been  improperly  car- 
ried out,  the  resulting  high  temperature  having  vitrified  the  corns,  or 
the  acrospire  has  not  been  sufficiently  grown  with  the  result  that  the 
grain  is  not  properly  modified.  Malt  should  be  free  from  broken  and 
damaged  corns  or  culms  (dried  rootlets). 


OF   THE 

UNIVERSITY 

; 


134  MALT   AND    MALT    LIQUORS. 

Chemical  Examination  of  Malt. — The  brewing  value  of  a  sample 
of  malt  is  chiefly  dependent  on  3  factors,  namely,  the  proportion  of 
soluble  or  extractive  matter  it  will  yield  to  water;  the  character  of  this 
extractive  matter;  and  the  di astatic  activity. 

The  proportion  and  composition  of  the  extractive  matter  are  in- 
fluenced by  many  conditions,  including  the  temperature  of  the  water 
used  for  mashing,  the  character  of  the  water,  the  proportion  employed, 
the  composition  of  the  original  malt,  and  the  temperature  at  which 
it  is  dried. 

In  1905  the  Council  of  the  Institute  of  Brewing  (/.  Inst.  of  Brewing, 
1906,  12,)  appointed  a  committee  to  report  upon  suitable  methods  for 
estimating  the  extract,  moisture,  diastatic  power,  colour,  and  percent- 
age of  ready-formed  sugars  in  malt.  As  these  procedures  are  now 
usually  carried  out  in  all  English  laboratories  associated  with  the 
malting  or  brewing  industries  they  may  be  regarded,  at  any  rate  for  the 
present,  as  "  standard  methods." 

Sampling. — It  is  obvious  that  samples  sent  for  analysis  should, 
so  far  as  possible,  be  fairly  representative  of  bulks,  and  this  requires 
the  more  care  when  the  bulks  are  large,  and  when  the  malt  contains 
any  appreciable  number  of  hard  corns,  and  further,  when  there  is  any 
marked  irregularity  in  curing. 

In  the  case  of  deliveries,  samples  should  be  drawn  from  at  least  one 
sack  in  every  10  if  the  consignment  amounts  to  over  100  sacks,  or  if 
the  parcel  be  smaller,  then  from  10  %  of  the  number  of  sacks.  The 
sample  should  be  withdrawn  not  from  the  surface  of  a  sack,  but  from 
a  depth  of  at  least  six  inches. 

These  bulk  samples  should  be  put  into  a  small  bin  or  other  suitable 
receptacle,  thoroughly  well  mixed  up  and  the  requisite  number  of 
samples  collected  in  clean  screw-stoppered  beer  bottles. 

If  uniform  results  are  to  be  obtained  it  is  essential  that  the  grists 
should  be  uniform;  accordingly  the  committee  advised  that  the 
Seek  Mill  set  at  25°  should  be  used.  In  order  to  allow  for  loss  in  the 
mill,  a  quantity  of  malt,  slightly  in  excess  of  that  required  for  each  deter- 
mination should  be  separately  weighed  and  ground.  Finally  the  exact 
amounts  of  grist,  subsequently  required  for  the  various  determinations, 
are  weighed  out.  It  is  not  permissible  to  grind  at  the  outset  sufficient 
malt  for  all  the  procedures  and  to  weigh  the  various  quantities  from 
this  grist. 

Extract. — 50  grm.  of  ground  malt  are  mashed  in  a  glass  beaker  of 


MALT.  !35 

about  500  c.c.  capacity  with  360  c.c.  of  distilled  wrater  previously  heated 
to  154°  to  155°  F.  The  beaker  is  covered  with  a  clock  glass,  and 
placed  in  a  water-bath,  so  that  its  contents  are  kept  at  a  temperature 
of  150°  F.  for  55  minutes.  The  mash  is  stirred  at  intervals  of  about 
10  minutes  during  this  time.  The  temperature  is  then  raised  to 
i58°F.  in  5  minutes,  and  the  whole  mash  washed  into  a  flask  gradu- 
ated to  5I51  c.c.,  cooled  to  60°  F.,  made  up  to  the  mark  with  distilled 
water  at  the  same  temperature,  well  shaken  and  filtered  through  a 
large-ribbed  paper.  The  sp.  gr.  of  the  filtrate  is  then  determined  at 
at  once  at  60°  F.,  compared  with  water  at  that  temperature.2 

If  preferred,  the  mashing  can  be  carried  out  directly  in  the  515  c.c. 
measuring  flask.  In  this  case  the  mash  should  be  shaken  at  intervals 
of  about  10  minutes. 

Colour  of  Wort. — For  this  determination  the  Lovibond  tintometer 
is.  employed.  The  above  wort,  filtered  perfectly  bright,  should  be  placed 
at  once  in  a  i-in.  cell,  and  its  tint  recorded  in  colour  units  of  the  series 
"52"  glasses.  The  experiment  should  not  be  carried  out  in  direct 
sunlight,  and  the  light  must  fall  equally  on  both  halves  of  the  white 
plate  so  that  both  fields — viz.,  the  malt-extract  field  and  the  standard 
field — are  equally  illuminated.  To  test  this,  the  glasses  and  the  cell 
should  be  reversed,  and  all  results  rejected  when  the  figures  do  not  agree, 
whichever  side  the  cell  is  placed. 

J.  L.  Baker  and  H.  F.  E.  Hulton  (/.  Inst.  of  Brewing,  1906, 12,302; 
ibid.,  1907, 13,  26)  have  drawn  attention  to  the  discrepancies  which  arise 
in  reading  the  colour  of  worts  and  beers  in  the  Lovibond  tintometer  when 
the  position  of  the  instrument  is  varied  relatively  to  the  illumination. 
It  is  recommended  that  the  tintometer,  in  a  horizontal  position,  be 
directed  to  a  north  window,  covered  with  a  piece  of  thin  white  tissue- 
paper,  and  that  the  opal  screen  provided  with  the  instrument  be  dis- 
carded. J.  W.  Lovibond  (ibid.,  1908,  14,  2)  has  recently  devised  a 
standard  lamp  which  claims  to  overcome  the  attendant  difficulties 
of  daylight  as  a  standard  source  of  illumination. 

Moisture. — About  5  grm.  of  ground  malt  are  weighed  out  in  a 
shallow  copper  vessel,  about  5  cm.  in  diameter  and  1.25  cm.  in  depth, 

aThe  grains  from  50  grm.  of  malt  are  supposed  to  occupy  a  volume  of  15  c.c. 

2In  warm  weather  it  is  inconvenient  to  weigh  a  specific-gravity  bottle  containing  a  liquid 
at  a  temperature  of  60°  F.;  65°  or  70°  F.  are  more  suitable  temperatures.  It  has,  however, 
been  pointed  out  by  G.  C.  Jones  (J.  Inst.  of  Brewing,  1908,  14,  9)  that  it  is  not  sufficient 
to  determine  the  weights  of  malt  extract  and  water  contained  by  the  pyknometer  at  the  same 
temperature.  The  results  so  obtained  must  be  corrected  for  the  difference  in  the  coeffi- 
cients of  expansion.  At  65°  F.  0.2  must  be  added  to  the  brewer's  pounds,  and  at  70°  F.  0.5. 
The  excess  sp.  gr.  over  water  ( — 1,000)  multiplied  by  3.36  gives  the  extract  in  brewers' 
pounds  per  standard  quarter  of  malt. 


136  MALT   AND    MALT    LIQUORS. 

and  kept  for  5  hours  in  a  boiling  water  oven,  allowed  to  cool  in  a  desic- 
cator, and  reweighed,  the  loss  in  weight  being  taken  as  the  moisture 
content  and  calculated  as  a  percentage  on  the  malt. 

Diastatic  Activity  (Lintner  Value). — The  measurement  of  dias- 
tatic  activity  is  based  on  Kjeldahl's  law  of  proportionality  (Compt. 
rend,  des  travaux  du  laboratoire  de  Carlsberg,  1879,  I,  109;  vide  also 
A.  R.  Ling,/.  Fed.Inst.  Brewing,  1896,  2,335).  When  working  with 
malt  diastase  Kjeldahl  found  that  if  the  production  of  maltose  does  not 
exceed  45  %  of  the  starch  used,  this  maltose  may  be  taken  as  a  measure 
of  the  diastatic  activity  of  the  solution. 

25  grm.  of  ground  malt  are  extracted  with  500  c.c.  of  distilled  water 
for  three  hours  at  70°  F.1  and  filtered.  The  first  100  c.c.  of  the 
filtrate  is  rejected.  3  c.c.  of  the  perfectly  bright  extract  are  allowed  to 
act  on  100  c.c.  of  a  2  %  solution  of  soluble  starch  at  70°  F.  for  an  hour 

in  a  200  c.c.  flask. 

%     • 

Preparation  of  Soluble  Starch. — Purified  potato  starch  is  digested  with  dilute 
hydrochloric  acid,  sp.  gr.  1,037,  at  the  room  temperature  (60°  to  65°  F.)  for  seven 
days,  stirring  the  mixture  daily.  500  grm.  of  starch  and  1,000  c.c.  of  dilute  acid 
being  suitable  quantities.  The  mass  is  washed  very  thoroughly  by  decantation, 
at  first  with  tap  water  and  later  on  with  distilled  water,  until  the  wash  water  is  free 
from  acid.  It  is  collected  on  a  filter-paper  placed  in  a  Buchner's  funnel,  pumped  as 
dry  as  possible,  and  then  spread  out  on  a  new  unglazed  plate.  The  starch  should 
be  dried  at  a  gentle  heat  (no0  F.)  as  quickly  as  possible.  When  dry,  the  starch  is 
triturated  in  a  porcelain  mortar  and  rubbed  through  a  fine  hair  sieve. 

Starch  Solution. — In  determining  diastatic  capacity,  the  starch  must  be  dis- 
solved in  boiling  water  at  the  rate  of  2  grm.  of  the  starch  per  100  c.c.  of  water;  the 
solution  is  then  cooled  to  70°  F.  for  use.  It  should  be  mobile  (not  gelatinous), 
indicating  perfect  conversion  into  soluble  starch,  and  showing  only  a  negligible 
reducing  action  on  Fehling's  solution;  and  it  should  be  neutral  to  litmus  solution. 

N/io  alkali  (10  c.c.)  is  then  added  in  order  to  stop  further  diastatic 
action,  the  liquid  cooled  to  60°  F.,  made  up  to  200  c.c.  with  distilled 
water  at  the  same  temperature,  well  shaken,  and  titrated  against  5  c.c. 
portions  of  Fehling's  solution,  using  ferrous  thiocyanate  as  indicator. 

The  method  of  titration,  which  was  devised  by  A.  R.  Ling  is  carried 
out  as  follows: 

5  c.c.  of  Fehling's  solution  (see  p.  318)  are  accurately  measured 
into  a  150  c.c.  boiling  flask,  and  raised  to  boiling  over  a  small  naked 
bunsen  flame.  The  converted  starch  solution  is  added  from  a  burette, 
in  small  quantities  at  first  of  about  5  c.c.,  the  mixture  being  kept 

xThe  water  used  for  this  extraction  and  also  for  the  preparation  of  the  starch  solution 
must  be  free  from  ammonium  compounds  nitrites  and  other  impurities  which  may  in- 
fluence diastatic  conversion.  The  water  should  be  redistilled  with  the  addition  of  a  little 
potassium  permanganate  and  sodium  hydroxide  until  the  distillate  is  pure  and  neutral  to 
litmus  solution.  G.  C.  Jones  (/.  Inst.  of  Brewing,  1908,  14,  12)  finds  that  alizarin  paste 
(i  grm.  in  200  c.c.)  is  a  more  satisfactory  indicator  than  litmus. 


DIASTATIC   ACTIVITY.  137 

rotated  and  boiled  after  each  addition  until  reduction  of  the  copper  is 
complete,  which  is  ascertained  by  rapidly  withdrawing  a  drop  of  the 
liquid  by  a  glass  rod  and  bringing  it  at  once  in  contact  with  a  drop  of 
the  indicator  on  a  porcelain  or  opal  glass  slab. 

The  results  are  calculated  by  the  following  formula: 


1000 

x  y 


in  which  A  equals  the  diastatic  activity,  x,  equals  the  number  of  cubic 
centimetres  of  malt  extract  contained  in  100  c.c.  of  the  fully  diluted 
starch  conversion  liquid,  and  y  equals  the  number  of  cubic  centimetres 
of  the  same  liquid  required  for  the  reduction  of  5  c.c.  of  Fehling's 
solution. 

The  above  method  (using  3  c.c.  of  malt  extract  to  100  c.c.  of  2  % 
soluble  starch  solution)  is  not  accurate  for  malts  having  a  diastatic 
capacity  exceeding  50  Lintner;  in  the  case  of  such  malts  the  relative 
volume  of  malt  extract  must  be  less,  say  2  c.c.,  or,  for  malts  of  the 
highest  diastatic  capacity,  such  as  are  frequently  used  by  distillers  and 
vinegar  makers  (i.e.,  malts  of  a  diastatic  power  of  over  80°  Lintner), 
an  even  smaller  volume  of  extract  must  be  taken. 

An  alternative  method  which  is  largely  employed  consists  in  measur- 
ing 10  c.c.  of  a  2  %  solution  of  soluble  starch  into  each  one  of  a 
series  of  eight  carefully  cleaned  test-tubes.  The  tubes  and  their  con- 
tents are  then  placed  in  a  suitable  stand  and  immersed  in  a  water-bath 
at  a  temperature  of  70°  F.  As  soon  as  the  starch  solution  has  reached 
this  temperature  o.i  c.c.  of  the  malt  extract  (prepared  as  before)  is 
measured  into  the  first  of  the  tubes.  The  second  tube  receives  0.2  c.c., 
the  third  0.3  c.c.,  and  so  on  until  the  eight  test-tubes  contain  malt  ex- 
tract in  regularly  increasing  quantities.  The  tubes  are  replaced  in  the 
stand  and  immersed  in  the  water  bath  at  70°  F.  for  exactly  one  hour 
from  the  time  the  malt  extract  was  added  to  the  first  tube.  To  each 
tube  is  then  added  5  c.c.  of  Fehling's  solution;  after  shaking,  the  tubes 
are  heated  in  a  boiling-water  bath  for  ten  minutes  and  allowed  to  stand 
until  the  cuprous  oxide  has  settled.  It  will  usually  be  noticed  that  the 
liquid  of  one  tube  in  the  series  is  faintly  blue,  showing  that  there  was 
insufficient  maltose  formed  to  reduce  the  copper  sulphate,  whilst  the 
succeeding  one  is  yellow  due  to  over-reduction.  If,  for  example,  tube 
3  was  under-reduced  as  much  as  tube  4  was  over-reduced,  the  reading 
would  be  taken  as  0.35  c.c.  Intermediate  points  are  judged  by  inspec- 
tion. Sometimes  the  solution  in  one  of  the  tubes  will  be  neither  blue 


138  MALT   AND    MALT    LIQUORS. 

nor  yellow,  showing  that  the  amount  of  maltose  formed  was  just 
enough  for  complete  reduction.  If  o.i  c.c.  of  malt  extract  corresponds 
to  a  diastatic  power  of  100  and  x  equals  the  quantity  of  malt  extract 
added  to  the  tube,  the  contents  of  which  occasioned  or  were  adjudged 
to  occasion  complete  reduction  of  the  Fehling's  solution,  then  the 
diastatic  power  of  a  sample  of  malt  may  be  calculated  from  the 
expression : 

o.i  X  100 
x 

It  is  customary  to  deduct  1.5  from  the  diastatic  power  found,  owing  to 
the  reducing  sugars  present  in  the  malt  extract.  When  highly  diastatic 
malts  are  examined  the  malt  extract  should  be  diluted  with  an  equal 
volume  of  water  and  the  reading  obtained  doubled. 

Cold  Water  Extract. — 25  grm.  of  ground  malt  are  digested  with 
250  c.c.  of  distilled  water  containing  20  c.c.  of  N/io  ammonium 
hydroxide  (i.e.,  20  c.c.  of  N/io  ammonium  hydroxide  made  up  to  250 
c.c.  with  distilled  water)  for  three  hours  at  70°  F.,  stirring  about  three 
or  four  times  during  this  period.  After  filtering,  the  sp.  gr.  of  the 
bright  filtrate  is  taken  at  60°  F.,  compared  with  water  at  the  same 
temperature.  The  excess  sp.  gr.  over  water  (  =  1,000),  corrected  for 
the  sp.  gr.  of  the  ammonium  hydroxide,  divided  by  3.86  and  multi- 
plied by  10  gives  the  cold  water  extract  per  cent. 

Considerable  importance  is  still  attached  by  many  brewing  chemists 
to  the  significance  of  the  percentage  of  matter  soluble  in  cold  water,  as 
it  is  claimed  to  be  an  indication  as  to  whether  a  malt  has  been  properly 
made.  If  the  growth  of  the  sprouted  barley  is  unduly  hastened 
on  the  malting  floor  (forcing)  more  of  the  starch  is  converted  into  sugar 
and  more  insoluble  matter  into  soluble  matter  than  if  the  growth  had 
been  slow.  Wet  loading  on  the  kiln  will  also  occasion  an  increase 
in  matters  soluble  in  water.  In  recent  years  doubts  have  been 
expressed  as  to  the  value  of  this  datum,  for  it  is  by  no  means 
proved  that  a  so-called  " forced  malt"  will  of  necessity  produce  an 
unsound  beer. 

The  soluble  matters  consist  of  proteins,  ash,  acid  and  "ready-formed 
carbohydrates"  (cane-sugar,  invert  sugar  and  maltose).  An  average 
figure  for  an  English  malt  is  18  %,  half  of  which  is  due  to  carbo- 
hydrates. 

Statements  of  Results. — The  results,  expressed  to  the  nearest 
first  decimal  place  only,  except  in  the  case  of  diastatic  activity,  which 


MALT.  139 

should  be  recorded  only  to  the  nearest  integer,  are  usually  set  out  as 
follows : 

Extract  per  standard  quarter,  brewers'  pound, 

Moisture,  per  cent., 

Diastatic  activity  (Lintner  value), 

Tint  (10  %  wort,  i  in.  cell,  "52"  series  Lovibond), 

Cold  water  extract  per  cent., 

In  addition  to  the  estimations  described  above,  the  following  afford 
information  of  a  useful  character. 

Acidity. — The  acidity  of  a  malt  is  calculated  as  lactic  acid,  which, 
however,  is  incorrect,  as  the  acid  reaction  of  most  malts  is  due  chiefly 
to  acid  phosphates.  The  estimation,  the  value  of  which  is  entirely 
empirical,  is  made  by  digesting  50  grm.  of  ground  malt  with  300  c.c.  of 
distilled  water  at  60°  F.  for  3  hours  and  measuring  the  acidity  of  the  fil- 
tered extract  by  means  of  N/20  ammonium  hydroxide,  using  litmus 
paper  as  an  indicator. 

Modification. — Malts  differ  considerably  in  the  extent  to  which 
modification  has  taken  place.  If  the  growth  has  been  insufficient  on 
the  floor  the  finished  malts  will  have  steely  ends,  and  these  will  not  yield 
the  full  extract  when  mashed,  as  the  starch  will  not  be  amenable  to  the 
action  of  diastase.  Modification  may  be  conveniently  measured  by 
mashing  a  fine  and  coarse  grind  of  the  same  malt  under  the  conditions 
previously  given.  In  a  well-made  malt  the  extracts  of  a  fine  and  coarse 
grind  will  be  practically  the  same,  in  steely  malts  the  differences  will  be 
considerable  (3  to  4  pounds  per  quarter). 

Nitrogenous  Constituents. — The  total  amount  of  nitrogenous 
matter  in  the  malt  (10  to  11%)  is  determined  by  KjeldahPs  method 
and  the  nitrogen  figure  found  multiplied  by  6.25.  The  insoluble 
nitrogenous  matter  is  the  difference  between  the  total  nitrogenous 
matter  and  that  soluble  in  water  Malt  contains  less  nitrogenous 
matter  than  the  barley  from  which  it  was  made  owing  to  the  loss 
during  germination.  The  soluble  nitrogenous  matter  in  barley  is 
about  5%;  in  malt  2.5%. 

The  "  Saccharification "  Test.— This  test  has  been  devised  to 
measure  the  time  required  for  the  complete  saccharification  of  a  malt 
mash.  10  grm.  of  the  ground  malt  are  mixed  with  100  c.c.  of  water 
at  154°  F.  and  kept  at  151°  F.  in  a  suitable  bath,  the  mash  being  stirred 
occasionally.  In  15  minutes  about  5  c.c.  of  the  mash  are  withdrawn, 
filtered  and  the  cooled  filtrate  tested  for  the  presence  of  starch  by  iodine. 
If  starch  is  found  the  test  is  repeated  at  intervals  of  5  minutes  until  the 


140  MALT   AND    MALT    LIQUORS. 

iodine  reaction  is  no  longer  observed.  The  time  taken  for  the  complete 
saccharification  is  then  noted.  (A.  J.  Brown,  Laboratory  Studies  for 
Brewing  Students,  62.) 

Dry  Grains. — The  concentration  of  the  wort  in  the  extract  estima- 
tion is  arrived  at  by  dividing  the  excess  gravity  above  1000  by  4.  As 
the  proportion  of  malt  used  to  water  was  as  10 : 100,  the  dry  extract 
multiplied  by  10  represents  the  dry  extract  in  100  grm.  of  malt.  The 
percentage  of  dry  extract  subtracted  from  100  gives  the  percentage 
of  dry  grains.  The  result  is,  of  course,  corrected  for  the  moisture  in 
the  malt. 

PHYSICAL  EXAMINATION. 

Growth. — 100  or  preferably  200  malt  corns  are  counted  and  sorted 
into  the  following  six  groups  according  to  the  development  of  the 
acrospire,  o  to  1/4;  1/4  to  1/2;  1/2  to  3/4;  3/4  to  i;  overgrown, 
and  damaged  corns.  The  length  of  the  acrospire  is  conveniently  ob- 
served by  feeling  the  husk  of  the  malt  corn  on  the  round  side  beginning 
at  the  germ  end.  In  well-made  English  malt  80  to  100%  of  corns  are 
from  3/4  to  fully  grown. 

The  "Sinker"  Test. — 500  corns  are  counted  and  stirred  into  a 
beaker  containing  cold  water.  The  corns  which  float  are  removed. 
Some  corns  will  lie  flat  on  the  bottom  of  the  beaker,  and  when  these 
are  examined  they  will  be  found  to  be  either  ungerminated  barley, 
very  steely,  or  vitreous  corns;  other  corns  may  rest  on  one  end  and 
these  will  probably  be  steely-tipped. 

Malt  should  be  free  from  impurities,  such  as  stones,  (which  fre- 
quently cause  explosions  during  the  grinding)  dirt,  or  foreign  seeds. 
Serious  arsenical  contamination  now  rarely  occurs.  If  present  in 
quantity  (a  safe  limit  is  1/300  grain  of  arsenous  oxide  per  pound) 
it  may  usually  be  traced  to  carelessness  on  the  part  of  the  maltster, 
such  as  mixing  gas  coke  with  the  anthracite.  For  the  estimation  of 
arsenic  in  malt  and  beer,  see  page  146. 

MALT  WORTS. 

Total  Solid  Matter. — The  sp.  gr.  of  a  malt  wort  is  ascertained  in 
the  laboratory  by  a  sp.  gr.  bottle,  and  this  figure  minus  1,000  (water  = 
1,000)  and  divided  by  4  gives  the  number  of  grm.  of  solid  matter 
(dry  extract)  contained  in  100  c.c.  of  the  wort. 


MALT    WORTS.  141 

For  the  purposes  of  the  brewer  the  sp.  gr.  of  the  wort  may  be  ascer- 
tained by  the  hydrometer,  various  modifications  of  which  have  been 
devised  for  this  purpose. 

Bates'  brewers'  saccharometer  is  an  instrument  the  indications  of 
which  are  expressed  in  "pounds  per  barrel,"  and  these  may  be  trans- 
lated into  absolute  gravities  by  dividing  the  number  of  "saccharometer 
pounds"  by  0.36  (or  multiplying  by  2.778)  and  adding  1000.  A  barrel 
(  =  36  gallons)  of  water  weighs  360  pounds;  a  beer- wort,  a  barrel  of 
which  weighs  380  pounds  (  =  360  +  20),  is  said  to  have  a  "saccharometer 
gravity  of  20  pounds  per  barrel."  The  real  sp.  gr.  of  such  wort  would 
be  1055.5;— for  360:380  =  1000  : 1055.5;  and  it  would  contain  13.8  grm. 
of  solid  extract  per  100  c.c.  or  50.1  pounds  per  barrel  of  36  gallons. 
Similarly,  a  wort  of  1055  sp.  gr.,  which  is  the  standard  strength  of  beer 
wort  on  which  the  duty  of  6s.  pd.  per  barrel  is  levied,  has  a  saccharom- 
eter gravity  of  20.52  pounds  per  barrel;  for  1055 — 1000  =  55;  an(i  55  X 
0.36=19.80. 

Corrections  of  sp.  gr.  of  beer  worts  for  temperature  can  be  made 
as  described  on  page  123. 

The  method  of  ascertaining  the  original  gravity  of  malt  or  beer  worts 
which  have  undergone  fermentation  is  described  on  page  151. 

The  solid  matter  of  malt  worts  consists  of  a  mixture  of  dextrins, 
sugars,  nitrogenous  matters  and  ash  constituents.  The  work  of  O'Sul- 
livan,  Brown  and  Morris,  Lintner,  Ling  and  many  others  has  shown 
how  very  complicated  are  the  products  formed  by  the  action  of  diastase 
on  starch. 

In  the  mash  tun,  maltose,  a  series  of  dextrins  differing  in  molecular 
weights  and  complexity  (the  so-called  malto-dextrins),  probably  dex- 
trose and  the  preexisting  carbohydrates  in  the  malt  are  present.  To 
follow  the  nature  of  the  conversion  in  the  mash  tun  by  fully  analysing 
the  wort  involves  an  amount  of  work  which,  in  the  opinion  of  the  writer, 
is  not  warranted  by  the  results  obtained.1 

Useful  data  for  control  purposes  are  furnished  by  the  specific  rotatory 
power  and  cupric  reducing  power  of  the  wort  and  from  these  the  per- 
centage of  apparent  maltose  and  apparent  dextrin  on  the  wort  solids 
may  be  calculated. 

Estimation  of  "Apparent  Maltose  and  Dextrin." — The  wort  is 
boiled  to  throw  out  any  coagulable  proteins,  filtered  and  the  sp.  gr. 

JMoritz  and  Morris  describe  an  elaborate  scheme  for  the  analysis  of  worts  in  Text-Book 
of  the  Science  of  Brewing. 


142  MALT   AND    MALT    LIQUORS. 

at  15.5/15.5°.     This  figure  minus  1,000  and  divided  by  4  will  give  the 
grm.  of  wort  solids  per  100  c.c. 

Specific  Rotatory  Power. — A  wort  light  in  colour  may  be  read 
directly  in  a  100  or  200  mm.  tube.  If  the  wort  should  be  dark  it  may 
be  clarified  with  basic  lead  acetate  or  alumina  cream  as  in  the  case 
of  raw  sugars.  Black  beer  worts  require  a  special  treatment,  as  basic 
lead  acetate  will  riot  remove  all  the  colour.  Heron  has  suggested 
treating  the  wort  with  bleaching  powder,  but  highly  caramelised  worts 
are  not  always  sufficiently  decolourised  by  these  means  for  reading  in  a 
polarimeter.  The  writer  has  found  that  any  black  wort  may  be  decol- 
ourised with  phosphotungstic  acid.  The  reagent  is  prepared  by 
dissolving  phosphotungstic  acid  in  water  and  adding  20  %  sulphuric 
until  there  is  a  slight  turbidity.  To  25  c.c.  of  the  original  black  wort 
4  c.c.  ofphosphotungstic  acid  are  added  and  10  c.c.  of  20  %  sulphuric 
acid.  The  contents  of  the  flask  are  made  up  to  100  c.c.  filtered  and 
read. 

Reducing  Power. — For  this  determination  the  conditions  advised 
by  Brown,  Morris  and  Millar  are  very  commonly  employed.  However, 
for  rapid  and  accurate  work,  the  volumetric  process  as  modified  by 
Ling  and  Rendle  (Analyst,  1908,  33,  167,  see  also  page  136)  may 
be  recommended,  and  if  carried  out  under  standard  conditions  the 
results  are  probably  quite  as  accurate  as  the  gravimetric  method 
(Ling  and  Jones,  ibid.,  1908,  33,  167). 

For  the  purpose  of  the  calculation  the  specific  rotatory  power  of 
maltose  is  taken  as  137  and  dextrin  as  200.  All  reducing  sugar  present 
is  supposed  to  be  maltose.  The  grm.  per  100  c.c.  of  maltose  X  1.37  = 
rotation  due  to  maltose.  The  total  reading  minus  that  due  to  the 
"apparent"  maltose  divided  by  2.00  =  dextrin  in  grm.  per  100  c.c. 

The  percentage  of  " apparent  maltose"  in  mash  tun  worts  calculated 
on  the  solids  varies  between  70  and  80,  the  "apparent  dextrin"  between 
4  and  10. 

ROASTED  MALT  AND  BARLEY. 

These  materials  are  used  principally  in  the  brewing  of  stouts;  small 
quantities  are  sometimes  added  to  a  pale  malt  grist  for  the  purpose  of 
adjusting  the  colour  of  a  beer.  For  technical  control  purposes  it  is 
customary  to  determine  extract,  colour  and  moisture. 

Colour. — 3  grm.  of  the  finely  divided  material  are  mixed  with  300 
c.c.  of  distilled  water  at  a  temperature  of  165°  F.,  allowed  to  stand 


MALT    SUBSTITUTES.  143 

ten  minutes  and  the  solution  read  in  a  1/4  in.  cell  in  the  Lovibond 
tintometer  and  the  resulting  figure  multiplied  by  2.  (J.  L.  Baker  and 
H.  F.  E.  Hulton,  /.  Inst.  Brewing,  1907,  13,  32.)  A  roasted  barley 
should  have  a  colour  of  at  least  60°.  Roasted  malts  are  frequently 
slightly  higher. 

Extract. — 25  grm.  each  of  roasted  barley  or  malt  and  a  pale  malt 
of  a  diastatic  power  not  exceeding  30°  are  mashed  together  under  the 
conditions  described  previously.  A  mash  of  the  pale  malt  is  made 
simultaneously.  The  gravity  is  deetrmined  of  the  extracts  and  that 
due  to  the  pale  malt  subtracted  from  the  extract  of  the  mixture.  The 
difference  multiplied  by  2  represents  the  extract  yielded  per  quar- 
ter (336  pounds)  of  the  roasted  malt  or  barley.  The  extract  figure 
varies  according  to  the  class  of  barley  or  malt  roasted  and  the  degree  of 
roasting.  With  a  colour  of  60°  the  extract  may  vary  between  75  and 
90  pounds  per  quarter  of  336  pounds. 

Moisture  is  estimated  in  the  same  manner  as  a  malt. 

Roasted  barley  is  now  largely  taking  the  place  of  roasted  malt,  the 
latter  being  used  mostly  in  the  brewing  of  export  stouts.  Since  roasted 
malt  is  more  expensive  than  roasted  barley,  it  is  necessary  to  see  that 
the  former  when  ordered  is  delivered.  Usually  this  can  be  done  by 
observing  if  the  acrospire  shows  any  sign  of  development.  The  lower 
nitrogen  content  of  roasted  malt  as  compared  with  barley  has  been 
proposed  as  a  means  of  differentiation,  but  the  wisdom  of  estimating 
nitrogen  in  bodies  which  have  been  submitted  to  such  high  temperatures 
as  to  be  charred  is  doubtful.  There  are  other  kinds  of  semi-roasted 
malt  used  in  brewing,  such  as  crystal  malt,  brown  malt,  etc.  They  may 
be  analysed  in  the  same  way  as  roasted  barley.  The  colour  should 
be  read  in  a  i  in.  cell. 

MALT  SUBSTITUTES. 

In  recent  years  many  of  these  preparations  have  been  placed  on  the 
market.  Most  of  them  are  derived  from  maize  or  rice.  The  starch 
in  the  grain  is  rendered  amenable  to  diastatic  action  by  being  submitted 
to  a  torrefaction  process;  that  is,  the  combined  action  of  moisture  and 
heat.  Since  these  substitutes  are  used  solely  for  the  extract  they  yield 
in  the  mash  tun  an  estimation  of  the  matter  capable  of  being  dis- 
solved by  malt  extract  is  of  importance. 

This  extract  may  be  measured  by  mashing  a  mixture  of  equal  weight 
of  flaked  maize  or  rice  or  1/3  flakes  and  2/3  malt  under  the  same 


144  MALT   AND    MALT    LIQUORS. 

conditions  as  a  black  malt  (see  above)  the  resulting  extract  due  to  the 
flakes  being  multiplied  by  2  or  3,  as  the  case  may  be.  It  is  preferable 
to  mash  equal  quantities  of  flakes  and  malt,  as  any  error  in  analysis  is 
multiplied  by  2  instead  of  3.  J.  L.  Baker,  (Brewers' Jour.,  1905,  41, 
186)  has  pointed  out  that  the  extract  obtained  from  flakes  differs  with 
the  diastatic  capacity  of  the  malt  employed.  If  deliveries  of  flakes  are 
controlled  by  analysis,  the  same  malt  should  be  used  by  the  chemist 
of  the  buyer  and  seller.  In  this  way  only  is  it  possible  to  obtain  compar- 
able results.  A  malt  of  a  diastatic  power  not  exceeding  30°  should  be 
used.  Briant  (/.  Inst.  of  Brew.,  1905,  II,  395)  suggests  mashing  the 
flakes  with  an  extract  prepared  by  digesting  a  pale  malt  of  a  diastatic 
power  of  3o°-4o°  Lintner  with  three  times  its  weight  of  cold  water  for 
90  minutes.  20  grm.  of  the  flakes  are  placed  in  a  beaker,  120  c.c.  of 
water  added  and  the  temperature  raised  to  160°  F.,  carefully  stirring 
during  the  time.  50  c.c.  of  the  cold  water  malt  extract  are  run  slowly 
in,  the  whole  mixed  and  allowed  to  stand  at  a  temperature  of  150°  F. 
for  2  hours.  The  mash  is  transferred  to  a  200  c.c.  flask,  cooled  to  60°  F., 
and  made  up  to  bulk,  filtered  and  the  sp.  gr.  taken.  This,  less  the 
gravity  due  to  the  added  malt  extract  (which  is  treated  in  a  similar 
manner)  represents  the  gravity  due  to  the  flakes.  The  excess  gravity 
multiplied  by  the  factor  3.32  will  give  the  extract  yielded  by  336  pounds 
of  the  flakes.  (The  volume  occupied  by  the  grains  from  20  grm.  of 
flaked  maize  is,  on  an  average  2.5  c.c.,  and  the  factor  has  been  calcu- 
lated after  allowing  for  this).  The  method  gives  satisfactory  results 

In  judging  the  suitability  of  flakes  for  brewing  purposes  the  amount 
of  oil  should  be  noted,  as  this  constituent  may  impart  an  unpleasant 
flavour  to  the  finished  beer.  The  oil  may  be  estimated  by  extracting 
5  grm.  of  the  finely  powdered  flakes  in  a  continuous  extractor  with 
ether  for  3  hours.  The  ether  is  evaporated  off  and  the  residual  oil  dried 
in  a  boiling  water-bath  for  i  hour,  cooled  in  a  desiccator  and  weighed. 
Carefully  prepared  flakes  contain  about  i%  of  oil;  if  more  than  2% 
is  present  they  are  not  suited  for  brewing. 

Moisture  is  estimated  as  in  malt.     An  average  figure  is  6  to  8  %. 

GRITS  AND  RAW  GRAIN. 

These  are  used  as  a  source  of  extract  in  some  breweries.  They  are 
treated  in  a  converter  to  gelatinise  the  starch,  cooled  to  a  convenient 
temperature  and  mashed  with  malt.  Such  materials  may  be  analysed 


MALT    EXTRACT.  145 

by  heating  with  water  preferably  under  pressure,  and  treating  the  starch 
paste  so  produced  with  malt  or  malt  infusion  of  known  extract.  Grits 
should  also  be  examined  for  oil  and  moisture. 


MALT  EXTRACT. 

Malt  extract  occurs  as  a  light  yellow  or  amber-coloured,  thick, 
viscid  liquid,  having  a  faint,  pleasant,  characteristic  odour,  a  sweet  muci- 
laginous taste  and  a  distinct  acid  reaction.  It  is  soluble  in  all  propor- 
tions in  water,  the  solution  being  precipitated  by  strong  alcohol.  Its 
diastatic  activity  is  destroyed  at  temperatures  above  65°. 

The  medicinal  value  of  malt  extract  depends  upon  the  proportion  of 
total  solid  nutritive  carbohydrates  it  contains  and  upon  its  diastatic 
action.  Many  of  the  extracts  on  the  market  contain  little  or  no 
diastase,  the  enzyme  having  been  destroyed  during  evaporation. 

The  following  analyses  of  commercial  preparations  were  made  by 
A.  R.  Ling  (Analyst,  1904,  29,  244): 

I  II  III  IV  V  VI 

Sp.  gr.  15.5  15.5°.  1395-70;    1395-12  I    1408.43!    1377-82 

per  cent.'per  cent,  per  cent,  per  cent.. per  cent,  per  cent. 


Maltose  (apparent)  

31  . 

j 

30  .  9 

24 

0 

27 

4 

34 

? 

25 

.  2 

Dextrose  .  . 

1  7  . 

2     \ 

18.2 

22 

0 

19 

I 

12 

.5 

20 

.  O 

Dextrin  (apparent)                         • 

8 

8  6 

10 

9 

S 

9 

9 

6 

.  7 

Unfermentable     matter    (e  x  - 
pressed  as  dextrin)  
Ash  
Water. 

4- 
I  . 
24  - 

5 
45 

•JQ 

3-5 
i  .49 
24  .67 

8 

I 
27 

1. 

5 
i 
24 

.3 

24 

'7* 

i 
29 

'.64 

•  S  2 

Diastatic  power  (Lintner)  

3O  . 

i 

27  .2 

32 

^ 

25 

r, 

39 

.7 

46 

Specific  rotatory  power  [a]n.  -  -  . 

91 

8° 

90-5° 

84 

.  2° 

86 

94 

-5° 

81 

.1° 

According  to  W.  J.  Sykes  and  C.  A.  Mitchell  (Analyst.,  1901,  26, 
230),  the  total  solids  range  between  75  and  82  %;  phosphoric  acid 
O^Os),  between  0.5  and  1.15,  and  total  nitrogen,  between  0.4  and  2.25. 
The  presence  of  dextrose  in  authentic  samples  of  malt  extract,  as  pointed 
out  by  Ling  (loc.  cit.),  is  of  importance  and  should  be  borne  in  mind 
when  adulteration  with  "glucose  syrup"  is  being  sought  for. 

The  liquid  malt  extracts  largely  sold  in  the  United  States  usually 
contain  but  a  small  amount  of  carbohydrates,  no  active  diastase,  and 
from  0.5  to  5%  of  alcohol. 

The  methods  for  the  estimation  of  total  solids,  ash  and  phosphoric 
acid  are  the  same  as  those  used  in  the  analysis  of  malt.  It  is  not  pos- 
sible to  estimate  the  sugars  in  terms  of  apparent  maltose  and  dextrin 
Vol.  I.— 10 


146  MALT   AND    MALT    LIQUORS. 

by  the  copper  method  in  conjunction  with  the  polarimeter.  Ling  (loc. 
cit.)  determines  the  dextrose  as  glucosazone  (see  under  sugar),  the  mal- 
tose being  calculated  from  the  reducing  power  less  that  due  to  the 
amount  of  glucose  found,  whilst  the  dextrin  is  calculated  from  the  rota- 
tory power  after  deducting  that  due  to  the  dextrose  and  maltose. 

Arsenic. — The  estimation  of  this  impurity  is  somewhat  out  of  place 
in  a  volume  devoted  to  "organic  analysis,"  but  since  the  alarm  occa- 
sioned by  the  arsenical  contamination  of  beer  in  1900  to  1901,  the 
testing  of  brewing  materials  and  beers  for  arsenic  has  become  a  matter 
of  routine.  Although  excellent  methods  have  been  devised  for  this, 
the  Marsh-Berzelius  process,  with  recent  improvements,  is,  in  the 
opinion  of  the  writer,  the  simplest.1 

The  reports,  minutes  of  evidence  and  appendices  on  the  Royal 
Commission  of  Arsenical  Poisoning,  1902,  may  be  regarded  as  a  text- 
book on  this  subject.  The  standard  electrolytic  method  is  described 
at  length  in  Appendix  21,  page  208  of  the  report. 

PREPARATION    OF   MATERIALS. 

Zinc. — Since  arsenic  is  frequently  present  in  zinc  it  is  necessary 
to  ascertain  if  the  latter  is  free  from  this  impurity  and  also  if  it  is 
sufficiently  sensitive,  or  in  other  words,  if  it  produces  a  normal  arsenic 
deposit  from  a  solution  containing  a  known  amount  of  arsenious  oxide. 
Before  use  the  zinc  must  be  granulated.  The  outer  surface  of  the 
ingot  is  cleaned  by  scraping,  then  treated  with  arsenic-free  hydro- 
chloric acid  and  well  washed  with  water.  The  zinc  is  melted  in  a 
porcelain  crucible  and  when  just  molten  it  is  poured  from  a  height 
of  about  4  feet  into  cold  water.  Chapman  (Analyst  1907,  32,  247.) 
has  proposed  the  addition  of  a  cadmium  salt  to  increase  the  sensitive- 
ness of  the  zinc.  Many  dealers  now  supply  granulated  zinc  sufficiently 
pure  to  be  used  in  the  estimation. 

Hydrochloric  Acid. — This  acid  unless  specially  purified  frequently 
contains  sufficient  arsenic  to  render  its  application  for  the  test  useless. 
The  method  devised  by  Thorne  (Proc.  Chem.  Soc.,  1902,  18,  118) 
works  well  in  practice.  Ordinary  strong  hydrochloric  is  diluted  with 
water  and  placed  in  a  large  retort.  Through  the  stoppered  opening 
is  introduced  a  glass  rod  carrying  on  the  end  a  piece  of  very  fine  copper 

1  This  method  is  similar  to  that  recommended  by  a  joint  committee  of  the  Society  of 
Public  Analysts  and  the  Society  of  Chemical  Industry  (J.  Soc.  Chem.  Ind.,  1902,  21,  94). 


ARSENIC    IN    MALT.  147 

gauze.  The  contents  of  the  retort  are  gently  boiled  for  an  hour, 
the  glass  rod  and  copper  gauze  removed,  a  small  piece  of  fresh 
gauze  added  and  the  acid  distilled.  The  first  100  c.c.  of  the 
distillate  should  be  rejected.  The  purified  acid  used  in  the  test 
should  have  a  sp.  gr.  i.i. 

Apparatus. — The  flask  is  fitted  with  a  ground-glass  stopper 
through  which  passes  the  stem  of  a  funnel  furnished  with  a  stop-cock. 
The  stopper  also  carries  the  exit  tube  on  which  is  a  bulb  and  which  is 
bent  twice  at  right  angles  and  connected  with  the  tube  containing  cal- 
cium chloride  and  a  plug  of  lead  acetate  paper.  The  hard  glass  tube  on 
which  the  arsenic  is  to  be  deposited  is  made  of  Jena  tubing  (external 
diameter  5  mm.),  drawn-out  portion  having  a  diameter  of  2  mm., 


FIG.  53. 

with  the  end  turned  up  at  right  angles.  A  piece  of  platinum  gauze 
should  be  wrapped  round  the  tube  at  the  point  at  which  it  is  to  be 
heated  by  the  Bunsen  flame. 

Preparation  of  the  Substances  to  be  Tested. — Unground  Malt. — 
40  grm.  of  the  malt  are  treated  at  a  temperature  of  50°  for  twenty 
minutes  with  40  c.c.  of  a  mixture  of  hydrochloric  acid,  sp.  gr.  i.i 
and  60  c.c.  of  water.  25  c.c.  of  the  supernatant  liquid  are  used  for 
the  test. 

Malt  Substitutes. — A  20  %  solution  of  glucose,  invert  sugar,  or 
caramel  is  made  and  acidified  with  hydrochloric  acid. 

Worts,  Commercial  Malt  Extracts,  and  Caramels. — It  is  usually 
preferable  to  destroy  the  organic  matter  in  these  materials  as  the  pres- 


148  MALT   AND    MALT   LIQUORS. 

ence  of  the  dextrinous  and  protein  matters  retards  the  formation  of 
hydrogen  arsenide.  The  destruction  of  these  substances  may  be 
effected  with  lime  and  magnesia  or  by  treatment  with  fuming  nitric 
acid  (compare  Rep.  Royal  Commission  on  Arsenical  Poisoning,  Appen- 
dix 21,  page  213). 

Hops  and  Hop  Substitutes. — A  weighed  quantity  is  treated  with 
dilute  hydrochloric  acid  and  an  aliquot  portion  of  the  extract  used  for 
the  test,  or  the  organic  matter  may  be  destroyed  by  incinerating  with 
lime  and  magnesia  and  the  ash  dissolved  in  hydrochloric  acid. 

Yeast  and  yeast  foods  are  treated  in  the  same  way  as  worts. 

Beers. — Generally  beers  may  be  introduced  directly  into  the  appa- 
ratus. Some  beers  of  high  gravity  behave  like  worts,  and  in  such  cases 
the  organic  matter  should  be  destroyed. 

Method  of  Working. — 10  grm.of  granulated  zinc  are  placed  in  the 
flask  A  and  covered  with  a  little  dilute  arsenic-free  hydrochloric  acid. 
After  the  action  has  proceeded  for  two  or  three  minutes,  it  is  well  washed 
and  the  necessary  connections  made.  10  c.c.  of  the  pure  hydrochloric 
acid  (sp.  gr.  i.i)  are  gradually  added.  At  the  end  of  10  minutes  the 
apparatus  will  be  practically  free  from  air,  and  the  issuing  hydrogen 
may.be  lighted.  At  the  same  time  the  burner  is  also  lighted,  and  the 
heating  of  the  hard  glass  tube  so  regulated  that  the  piece  of  platinum 
gauze  is  maintained  at  a  red  heat.  Then  during  20  minutes  a  further 
quantity  of  10  c.c.  of  hydrochloric  acid  is  added.  The  hydrogen 
flame  should  be  from  2  to  3  mm.  in  height  and  the  acid  is  to  be  added 
throughout  the  experiment  so  as  to  secure  this.  During  the  20  minutes 
heating  of  the  tube  a  deposit  of  arsenic,  best  seen  by  holding  a  white 
card  beneath  the  tube,  will  be  formed  if  the  zinc  or  acid  is  not  arsenic- 
free.  In  such  a  case  the  experiment  must  be  discontinued,  the  flask 
washed  out  and  fresh  materials  employed. 

When  the  materials  are  thus  proved  to  be  free  from  arsenic,  the  solu- 
tion to  be  tested  is  gradually  run  in,  so  that  its  addition  to  the  generating 
flask  is  spread  over  a  period  not  exceeding  1 5  minutes,  and  the  hydrogen 
flame  is  maintained  at  a  height  of  2  to  3  mm.  When  the  whole  of  the 
solution  has  been  added,  the  generation  of  the  hydrogen  is  continued  for 
another  15  minutes  at  least,  by  the  addition,  as  required,  of  more  hydro- 
chloric acid.  For  that  purpose  from  10  to  15  c.c.  are  needed. 

Preparation  of  the  Standard  Deposits. — The  standard  deposits 
with  which  the  arsenic  deposits  from  tested  substances  are  to  be  com- 
pared must  be  prepared  by  the  use  of  a  specimen  of  each  kind  of  sub- 


BEER   AND   ALE.  149 

stance  containing  known  amounts  of  arsenous  oxide.  The  quantity 
of  substance  taken  and  the  manner  of  preparing  the  solution  or  ex- 
tract must  be  the  same  as  described  under  the  test  for  that  substance. 
Every  care  should  be  taken  that  the  period  of  time  over  which  the  solu- 
tion is  added,  the  size  of  the  hydrogen  flame,  the  mode  and  duration  of 
heating  of  the  glass  tube,  and  the  amount  of  acid  used,  should  be 
the  same  in  the  preparation  of  the  series  of  the  standard  deposits  as  in 
the  carrying  out  of  the  actual  test.  The  mirrors  as  soon  as  deposited 
should  be  sealed  at  both  ends  in  an  atmosphere  of  hydrogen  and  kept 
in  the  dark.  According  to  the  experience  of  the  writer  the  standard 
mirrors  remain  practically  permanent  for  three  months. 

The  standard  arsenic  solution  is  prepared  by  dissolving  o.i  grm.  of 
pure  arsenous  oxide  in  a  small  quantity  of  pure  strong  hydrochloric 
acid.  The  liquid  should  not  be  heated.  When  the  solution  is  com- 
plete it  is  diluted  to  1000  c.c.  with  distilled  water,  i  c.c.  of  this  solution 
contains  o.i  mg.  of  arsenous  oxide. 


MALT  LIQUORS. 

Beer,  Ale. 

Beer  may  be  described  as  a  fermented  liquor  brewed  from  malt 
or  from  a  mixture  of  malt  and  malt  substitutes  and  having  a  bitter 
flavour  communicated  by  hops  or  by  other  wholesome  bitter.  In  the 
Middle  Ages  ale  was  a  fermented  infusion  of  malt  and  water  flavoured 
with  a  small  quantity  of  some  bitter  principle,  such  as  oak  bark.  Beer, 
on  the  other  hand,  was  made  from  malt,  water  and  hops.  The  distinc- 
tion between  ale  and  beer  lasted  for  a  considerable  time.  Hops  grad- 
ually came  into  general  use,  but  the  word  ale  was  retained  whether 
the  liquor  designated  by  it  was  hopped  or  not.  The  word  "beer" 
now  includes  all  malt  liquors,  whilst  ale  includes  all  but  black  or 
brown  beers. 

Under  the  present  law  of  England,  the  malt  of  typical  beer  may  be 
replaced  by  any  saccharine  or  amylaceous  substance,  and  as  the  duty  is 
levied  on  the  quantity  of  soluble  carbohydrates  made  into  beer,  as  de- 
termined by  the  sp.  gr.  of  the  infusion,  the  exact  nature  of  the  ferment- 
able matter  employed  is  a  matter  of  indifference  to  the  Excise.  Simi- 
larly, the  employment  of  hops  is  not  insisted  on  by  the  Excise,  and  any 
wholesome  bitter  (e.g.,  quassia  and  gentian)  can  be  employed.  The 


150  MALT   AND    MALT    LIQUORS. 

substitution  is  not  an  infringement  of  the  Sale  of  Food  and  Drugs  Act, 
which  could,  however,  be  enforced  in  the  case  of  a  distinctly  unwhole- 
some bitter  being  used.  It  may,  however,  be  pointed  out  that  hop 
substitutes  are  only  employed  to  a  very  slight  extent  in  breweries;  ac- 
cording to  the  Excise  returns  of  last  year  63,936,409  pounds  of  hops 
were  used  for  brewing  and  only  29,502  pounds  of  hop  substitutes. 

The  chemical  composition  of  beer  and  other  malt  liquors  is  very 
complex,  the  main  constituents  may  be  conveniently  arranged  in  the 
following  three  classes: 

a.  The  volatile  constituents;  including  alcohol,  water,  acetic  acid, 
carbonic  acid  and  some  other  acids. 

b.  The  fixed  organic  matters,  forming  the  organic  constituents  of 
the    " extract";    including   sugars,    dextrins    and   dextrinoid   bodies, 
glycerol,  lactic  and   succinic  acids,  proteins,   and  organic  extractive 
matters  from  hops,  etc. 

c.  The  mineral  constituents  or  ash;  consisting  chiefly  of  potassium, 
calcium,  and  magnesium  phosphates. 

Beer  differs  from  wine  in  its  smaller  content  of  alcohol,  and  the  greater 
proportion  of  dextrin  and  other  extractive  matters  present ;  also  in  the 
absence  of  acid  tartrates,  which  are  characteristic  of  wine  as  malic 
acid  is  of  cider  and  lactic  acid  of  beer.  The  acidity  of  beer  is  frequently 
ascribed  to  acetic  acid,  but,  except  in  sour  ales,  it  is  chiefly  due  to  lac- 
tic acid,  to  other  organic  acids  produced  by  fermentation,  and  acid 
phosphates. 

The  composition  of  malt  liquors  differs  widely  according  to  the 
nature  and  proportion  of  the  materials  used  and  the  manner  in  which 
the  fermentation  has  been  conducted.  Broadly  speaking,  two  distinct 
methods  of  brewing  are  pursued,  namely,  the  German  and  the  English. 
German  beers  are  fermented  at  a  low  temperature,  under  which  con- 
dition the  yeast  remains  at  the  bottom  of  the  liquid,  and  the  process  is 
said  to  be  one  of  " bottom-fermentation."  The  yeast  is  a  different 
variety  from  that  of  English  breweries.  Beer  brewed  on  this  system 
contains  less  alcohol  and  more  dextrin,  sugar,  and  nitrogenous  matter 
than  English  beer,  and  hence  is  liable  to  undergo  secondary  fermen- 
tation unless  kept  at  a  very  low  temperature  or  else  sterilised  and 
preserved  in  bottles.  The  German  beer  also  contains  less  hops  than 
English  beer.  In  the  English  system  of  brewing,  the  operation  is  one 
of  "top-fermentation,"  and  as  a  rule  the  product  is  richer  in  alcohol 
and  contains  less  extractive  matter  than  German  beer. 


BEER.  151 

Generally,  bitter  ales  have  a  low  attenuation,  high  percentage  of 
alcohol  and  much  hop  extract;  mild  ales  higher  attenuations,  less  alcohol 
and  less  hop  extract;  porter  about  the  same  attenuation  as  mild  ale, 
but  less  hops.  Stouts  usually  have  a  high  attenuation  and  low  alcohol 
content;  they  are  hopped  in  proportion  to  their  gravity.  Export  ales 
and  stouts  have  low  attenuations  and  "high  content  of  alcohol  and  are 
heavily  hopped.  A  lengthy  list  of  the  different  beers  of  the  world  and 
their  analyses  may  be  found  in  Wahl  and  Henius'  Handy  Book  of 
Brewing  and  Malting.  A  full  analysis  of  a  beer  is  useful  for  technical 
control  purposes,  but  given  two  beers  brewed  at  the  same  gravity  it  is 
not  possible,  in  the  opinion  of  the  writer,  to  adduce  figures  to  show  that 
one  is  of  superior  quality  to  the  other.  An  analysis  will  give  some  in- 
formation as  to  how  a  beer  was  brewed  and  it  is  also  possible  by  the 
"  Forcing  Test,"  which  will  be  described  later,  to  form  an  idea  as  to  the 
stability  of  a  beer  and  how  it  will  behave  in  the  trade. 

Original  Gravity  of  Beer- worts. — As  the  duty  on  beer  is  calculated 
from  the  strength  of  the  wort  as  indicated  by  its  sp.  gr.,  it  becomes 
necessary  to  allow  a  rebate  or  drawback  when  the  beer  is  exported. 
If  the  wort  could  always  be  examined  in  an  unfermented  state,  it  would 
merely  be  necessary  to  ascertain  its  density  and  gauge  its  measure  to 
obtain  the  data  for  calculating  the  allowance  to  be  made.  But  by  the 
process  of  fermentation  the  sp.  gr.  of  the  wort  is  diminished  to  an 
extent  dependent  on  the  amount  of  alcohol  formed.  The  weight  of 
alcohol  produced  being  approximately  50  per  cent,  of  the  saccharine 
matter  destroyed  by  the  fermentation,  it  is  evident  that  a  determina- 
tion of  the  alcohol  in  the  fermented  liquid  would  give  the  means  of 
ascertaining  the  quantity  of  sugar  destroyed,  and  hence  of  making  the 
necessary  correction  for  the  reduction  in  the  density  of  the  wort  (tech- 
nically called  its  "attenuation")  caused  by  the  fermentation.  ggft 
The  practical  details  of  the  methods  of  estimating  the  original 
gravities  of  beer  worts  have  been  investigated  by  Graham,  Hofmann, 
and  Redwood,  and  their  results  show  that  that  the  information  can  be 
obtained  in  the  following  manner: 

Distillation  Method. — The  carbon  dioxide  is  first  removed  from  the 
sample  of  beer  to  be  examined  by  "tossing,"  that  is  pouring  from 
one  beaker  to  another,  or  by  filtering  through  paper  or  a  plug  of 
glass  wool. 

100  c.c.  of  the  beer  at  a  temperature  of  60°  F.  are  introduced 
into  the  distilling  flask  (Fig.  54)  of  the  original  gravity  apparatus  by'a 


152 


MALT   AND    MALT    LIQUORS. 


pipette,  40  c.c.  of  water  added  and  distillation  is  continued  until  about 
80  c.c.  have  passed  over.  The  distillate  is  made  up  to  100  c.c. 
at  60°  F.  and  the  sp.  gr.  determined.  The  residue  in  the  distilling 
flask  is  cooled  and  transferred,  together  with  washings,  into  a  100  c.c. 


FIG.  54. 

flask  made  up  to  volume  with  water  at  60°  F.  and  the  sp.  gr.  ascertained. 
The  sp.  gr.  of  the  distillate  represents  the  fermented  matter  as  a 
mixture  of  alcohol  and  water,  and  that  of  the  residue  the  unfermented 
matter  in  the  original  wort.  To  find  the  amount  of  fermented  matter 


BEER. 


the  sp.  gr.  of  the  alcohol  distillate  is  subtracted  from  1,000  and  the  dif- 
ference is  the  "spirit  indication  number"  (see  Table  I).  From  this 
table  the  number  of  degrees  of  sp.  gr.  lost  during  fermentation  which 
correspond  to  the •" spirit  indication"  may  be  found.  This  number 
plus  the  sp.  gr.  of  the  unfermented  matter  represents  the  original  gravity 
of  the  wort. 


TABLE  I. 

SPIRIT  INDICATION  TABLE  SHOWING  DEGREES  OF  GRAVITY 
LOST  IN  MALT  WORT  DURING  FERMENTATION. 


Degrees 
of  Spirit 
Indica- 
tion. 

.0 

.1 

.2 

•3 

•4 

•5 

.6 

•7 

.8 

•9 

0 

j 

•j    o 

•3 

32 

.6 

•9 

I  .2 

1.5 

1.8 

5T 

2.1 

5c 

2.4 

5Q 

2-7 

6  .  2 

2 

1:1 

•o 

7.0 

7-4 

7-8 

8.2 

8.6 

•* 
9.0 

•D 
9.4 

•y 
9.8 

10.2 

3 

10.7 

II  .1 

"•5 

12.0 

12.4 

12.9 

J3-3 

I3.8 

14.2 

14.7 

4 

!5-i 

»S-5 

16.0 

16.4 

16.8 

17-3 

17.7 

18.2 

18.6 

I9.I 

5 

J9-5 

19.9 

20.4 

2O.9 

21.3 

21.8 

22.2 

22.7 

23.1 

23-6 

6 

24.1 

24.6 

25.0 

25-5 

26.0 

26.4 

26.9 

27.4 

27.8 

28.3 

7 

28.8 

29.2 

29.7 

30.2 

3°-7 

31.2 

31-7 

32.2 

32-7 

33-2 

8 

33-7 

34-3 

34-8 

35-4 

35-9 

36.5 

37-° 

37-5 

38.0 

38.6 

9 

39-i 

39-7 

40.2 

40.7 

41.2 

41.7 

42.2 

42.7 

43-2 

43-7 

10 

44.2 

44-7 

45-i 

45-6 

46.0 

46.5 

47.0 

47  -.5 

48.0 

48.5 

ii 

49.0 

49.6 

50-1 

50.6 

51-2 

5i-7 

52.2 

52.7 

53-3 

53-8 

12 

54-3 

54-9 

55-4 

55-9 

56.4 

56.9 

57-4 

57-9 

58.4 

58.9 

J3 

14 

59-4 
64.8 

60.0 
65-4 

60.5 
65-9 

61.1 
66.5 

61.6 
67.1 

62.2 
67.6 

62.7 
68.2 

li.l 

63.8 
69-3 

64-3 
69.9 

15 

70-5 

71.1 

71.7 

72-3 

72.9 

73-5 

74.1 

74-7 

75-3 

75-9 

The  experimental  data  on  which  the  table  was  constructed  included 
the  formation  of  o.i  %  acidity  calculated  as  acetic  acid,  and  no  cor- 
rection is  necessary  in  the  case  of  beers  containing  about  this  propor- 
tion. Any  excess  of  acidity  over  o.i  %  is  supposed  to  be  formed  at  the 
expense  of  the  alcohol  in  the  beer,  and  unless  this  acidity  is  allowed  for 
the  original  gravity  will  be  low.  The  amount  of  acid  present  in  the 
beer  is  estimated  by  N/io  ammonium  hydroxide  using  litmus  paper 
as  an  indicator.  From  the  result  0.1%  is  subtracted  and  the  differ- 
ence referred  to  Table  II  which  indicates  the  correction  due  to  the 
excess  of  acid  formed.  This  number  is  then  added  to  the  spirit 
indication  figure. 


154 


MALT   AND    MALT    LIQUORS. 


TABLE  II. 

TABLE  FOR  ASCERTAINING  THE  CORRECTION  FOR  ACID. 


Ml 

Corresponding  Degrees  of  Spirit  Indication. 

w  g'§ 

.00 

.01 

.02 

•°3 

.04 

.05         .06 

.07 

.08 

.09 

u 

: 

.0 

.02 

.04 

.06 

.07 

.08 

.09 

.11             .12 

•  13 

.1 

.14 

•15 

•17 

.18 

.19 

.21 

.22 

•23 

.24 

.26 

.2 

•27 

.28 

.29 

•31        -32 

•33 

•34 

•35 

•37 

•38 

.3 

•39 

.40 

.42 

•43 

•44 

.46 

•47 

.48 

•  49 

•5i 

•4 

•52 

•53 

•55 

•56         -57 

•592 

.60 

.01 

.62 

.76 

•65 

.66 

.67 

-69 

.70 

.72 

•73 

•75 

.64 

•  7 

•77 
.90 

.78 
.91 

.80 
•93 

.81 
•  94 

.82 
•95 

.84 
•97 

a 

.86 
•99 

.87 

I.  00 

.89 

1.02 

.8 

1.03 

1.04 

1-05 

1.07 

i  .  08      i  .  09 

I  .10         I  .11 

i  .13 

I     14 

•9 

1.16 

1.18      1.19 

I.  21         1.22 

1.23    1.25 

1.26 

1.28 

I  .0 

1.29 

1.31      1.33      1.35 

r-36      i-37 

1  .38      1  .40      1  .41      1  .42 

When  a  beer  has  become  very  acid  with  acetic  acid  it  is  necessary  to 
make  allowance  in  respect  of  it;  firstly,  because  some  of  the  alcohol 
formed  has  been  lost  by  being  converted  into  acetic  acid  and,  secondly, 
because  the  acetic  acid  will  distil  over  with  the  alcohol  and  raise  the 
sp.  gr.  of  the  distillate  and  consequently  reduce  the  apparent  spirit  indi- 
cation and  also  the  original  gravity.  In  such  cases,  Moritz  and  Morris 
(Text-Book  of  the  Science  of  Brewing,  p.  503)  advise  that  a  second 
distillation  be  performed  in  presence  of  sufficient  alkali  to  neutralise 
the  acid  and  so  prevent  the  distillation  of  the  acetic  acid.  To  make  a 
correction  for  the  loss  of  alcohol  by  conversion  into  acid  the  acetic  acid 
is  estimated  as  follows:  100  c.c.  of  the  beer  are  taken  and  titrated  with 
ammonia  of  998.6  sp.  gr.,  red  litmus  paper  being  used  as  an  indicator. 
Each  c.c.  of  ammonia  used  represents  o.i  of  acetic  acid.  This  will 
give  the  total  acid  of  the  beer  calculated  as  acetic  acid.  100  c.c.  of 
beer  are  evaporated  to  dryness  on  a  water  bath,  the  residue  redis- 
solved  in  water  and  titrated  as  before.  This  gives  the  fixed  acid  cal- 
culated as  acetic  acid.  The  difference  between  the  two  gives  the 
volatile  acid,  or  real  acetic  acid.  The  above  percentage  of  acid  is  then 
referred  to  the  table  above  for  corresponding  loss  of  spirit  indication, 
and  this  spirit  indication  is  then  added  to  that  obtained  by  distillation. 
The  method  of  calculation  will  be  seen  from  the  following  example : 


BEER.  155 

Sp.  gr.  of  water  at  60°  F..  1000.0 

Sp.  gr.  of  distillate  at  60°  F.,  989.0 

Difference  = ' '  spirit  indication* "  1 1 .  o 

Allowance  for  alcohol  corresponding  to  0.2  %  excess  of  acid,  .27 

Corrected  spirit  indication,  11.27 

Equal,  by  table,  to  "gravity  lost,"  50.4 

To  which  add  sp.  gr.  of  extract,  1041 .3 

Original  gravity  of  wort,  1091 .7 

The  table  already  given  (page  153)  is  the  only  one  legalised  for  the 
determination  of  original  gravities,  and  is  used  by  the  Excise,  without 
correction,  whether  the  wort  be  derived  wholly  or  partly  from  starch- 
or  cane-sugar,  or  simply  from  malt.  This  practice  gives  the  brewer  the 
advantage  of  any  error. 

With  worts  containing  yeast  which  have  just  started  fermentation 
the  results  are  fairly  accurate,  but  the  original  gravities  of  finished 
beers  are  usually  about  2°  too  low.  It  cannot  be  expected  that  a  par- 
tially fermented  and  fully  fermented  mixed  malt  and  sugar  wort  will 
give  the  same  original  gravity,  as  the  ratio  of  residual  matters  left  after 
fermentation  to  the  alcohol  is  different  with  malt  worts  as  compared 
with  sugar  worts. 

Evaporation  Method. — In  employing  this  process,  the  sp.  gr.  of 
the  original  beer  is  first  carefully  ascertained,  taking  care  to  agitate 
the  liquid  well  to  eliminate  as  much  carbonic  acid  as  possible."  The 
''extract  gravity"  is  next  determined.  For  this  purpose  there  is  no 
occasion  to  boil  the  sample  in  a  closed  vessel,  as  it  is  not  required  to 
collect  the  volatilised  spirit.  It  is  simply  necessary  to  evaporate  suffi- 
ciently to  insure  the  entire  expulsion  of  the  alcohol,  and  then  allow 
the  liquid  to  cool,  and  make  it  up  exactly  to  the  original  bulk  of  the 
beer  taken.  The  sp.  gr.  is  then  observed,  and  the  corresponding 
"spirit  indication"  ascertained  by  subtracting  the  sp.  gr.  of  the  original 
beer  from  that  of  the  "extract."  The  necessary  allowance,  if  any, 
for  excess  of  acid  above  0.1%  must  next  be  made  as  in  the  dis- 
tillation method,  and  from  the  corrected  spirit  indication  the  corre- 
sponding number  of  degrees  of  gravity  lost  is  ascertained  by  reference 
to  the  table  already  given.  The  result  thus  obtained  is  not  in  strict 
accordance  with  that  by  the  distillation  method,  and  requires  to  be  cor- 
rected by  an  addition  of  1/40  to  the  "degrees  of  gravity  lost"  as  as- 
certained by  the  table.  Thus,  if  the  corrected  spirit  indication  be  9.4, 


156  MALT   AND    MALT   LIQUORS. 

corresponding  to  41.2  degrees  of  gravity  lost,  the  last  figure  requires  a 
correction  of  4|^?  =  1.03,  which,  added  to  41.2  raises  it  to  the  cor- 
rected number,  42.03  degrees.  The  following  example  illustrates  the 
whole  mode  of  calculation: 


Sp.  gr.  of  "extract"  1044.7 

Sp.  gr.  of  original  beer,  1035  .2 


Difference  =  "spirit  indication"  9 . 5 

Allowance  for  excess  of  acidity,  o.i 

Corrected  spirit  indication,  9 . 6 
Corresponding  "gravity  lost"  (by  table),      42.2 

Correction  of  1/40  of  above  number,  I-°SS 

Corrected  gravity  lost,  43  . 25 

Sp.  gr.  of  extract,  1044.7 


Original  gravity  of  wort,  1087 .95 

The  results  by  the  evaporation  process  are  not  generally  so  reliable 
or  so  constant  on  repetition  as  those  by  the  distillation  method,  but  they 
are  obtained  with  great  facility,  the  only  additional  operation  necessary 
being  the  determination  of  the  density  of  the  original  beer,  and  hence 
the  calculation  should  never  be  omitted,  as  it  furnishes  a  valuable  check 
on  the  distillation  process. 

The  Optical  Method  of  Determining  Alcohol  and  Extract  in 
Beer. — At  the  request  of  the  Norwegian  Government,  H.  Tornoe  un- 
dertook the  task  of  devising  a  rapid  and  simple  method  of  beer  analysis 
for  revenue  purposes.  He  elaborated  a  process  whereby  the  amount 
of  alcohol  and  extract  in  a  beer  can  be  ascertained  in  about  10  minutes. 
The  measurements  involved  are  the  sp.  gr.  of  the  beer  at  63.5°  F.  and 
the  index  of  refraction  of  the  beer  for  sodium  light  at  the  same  tempera- 
ture. The  principles  involved  and  the  use  of  the  instrument  have  been 
fully  described  by  Ling  and  Pope  (/.  Fed.  Inst.  of  Brewing,  1901,  7, 
170).  The  agreement  between  the  original  gravities  as  determined 
by  Tornoe's  method  and  the  distillation  method  is  satisfactory. 
(Compare  also  Race,  /.  Soc.  Chem.  Ind.,  1908,  27,  544.) 

Estimation  of  Alcohol.— The  amount  of  alcohol  in  a  fermented 
wort  or  beer  is  obtained  by  referring  the  sp.  gr.  of  the  alcoholic  distillate 
such  as  is  obtained  in  the  original  gravity  determination  (see  page  151) 
to  the  alcohol  tables  which  show  the  weight  of  alcohol  corresponding 
to  a  given  sp.  gr.  of  aqueous  alcohol;  from  the  weight  found  that  of 
.alcohol  in  100  c.c.  of  the  original  beer  is  calculated. 


BEER.  157 

Estimation  of  Extract. — The  proportion  of  extract  or  matter  re- 
maining in  a  beer  may  be  deduced  from  the  sp.  gr.  of  the  de-alcoholised 
liquid  obtained  by  evaporating  the  sample  to  one-third  and  diluting 
again  to  its  original  bulk.  The  sp.  gr.  of  the  extract  is  then  observed,, 
and  the  excess  above  1,000  divided  by  4,  the  quotient  being  the  number 
of  grms.  of  dry  extract  contained  in  100  c.c.  of  the  beer.  Or  the  residue 
left  in  the  distillation  flask  in  the  original  gravity  determination  may 
be  used  for  this  purpose.  The  "apparent  maltose"  and  "apparent 
dextrin"  may  be  determined  in  the  extract  in  the  manner  described 
on  page  141 

The  Amount  of  Unfermentable  Matter  in  a  Beer. — This  deter- 
mination is  of  value  in  forming  an  opinion  as  to  the  probable  course 
of  the  so-called  "secondary"  fermentation,  and  the  resulting  condition 
of  the  beer.  When  systematically  made  it  also  affords  information 
of  the  suitability  of  the  pitching  yeast  used  in  a  brewery. 

100  or  200  c.c.  of  the  beer  are  evaporated  until  the  alcohol  is  re- 
moved, made  up  to  the  original  volume  and  fermented  with  i  or  2 
grms.  of  pressed  yeast  for  48  hours.  The  solution  is  then  boiled  to  expel 
alcohol,  made  up  to  the  original  volume  with  water  and  a  small  quantity 
of  alumina  cream  and  filtered.  The  grm.  of  maltose  per  100  c.c.  are 
then  determined  from  the  reducing  power  (see  page  136)  and  the  differ- 
ence in  the  amount  of  maltose  before  and  after  fermentation  represents 
the  amount  of  fermentable  matter  remaining  in  the  beer.  This  differ- 
ence, although  conveniently  expressed  as  maltose,  includes  easily  fer- 
mentable low-type  malto-dextrins,  etc. 

Total  Nitrogen. — This  may  be  estimated  by  the  Kjeldahl  process. 
25  c.c.  of  the  beer  are  evaporated  to  a  small  bulk  in  the  flask  in  which 
the -decomposition  with  sulphuric  acid  is  carried  out,  a  few  drops  of 
dilute  sulphuric  acid  added,  and  the  whole  taken  nearly  to  dryness 
and  then  heated  with  20  c.c.  of  strong  sulphuric  acid  and  potassium 
sulphate  in  the  usual  way.  The  nitrogen  multiplied  by  the  factor  6.25 
gives  the  total  protein  percentage. 

Estimation  of  Carbon  Dioxide  in  Beer. — Since  carbon  dioxide 
may  be  regarded  as  the  natural  preservative  in  beer  its  estimation  is  of 
some  importance.  English  beers  in  cask  contain  between  0.25  and  0.35 
per  cent,  carbon  dioxide;  if  there  is  less  than  0.2  %  the  beer  tastes 
flat.  Windisch  (Das  chemische  Laboratorium  des  Braners,  page  326) 
describes  the  following  process  (Fig.  55)  which  gives  satisfactory  results: 

A  known  weight  of  beer,  about  300  grm.,  is  placed  in  the  flask  "A." 


158  MALT   AND    MALT    LIQUORS. 

The  screw  clip  "a"  which  is  closed  in  the  first  part  of  the  estimation 
controls  the  entry  of  air  from  the  soda-lime  tower  "T";  "b"  and  "b" 
connect  with  the  condenser  "B."  When  the  contents  of  the  flask  are 
boiled  most  of  the  alcohol  and  steam  is  condensed  by  means  of  "B"; 
the  calcium  chloride  tube  UC"  retains  any  aqueous  vapour  which  may 
escape.  The  bulbs  "  D  "  contain  strong  sulphuric  acid  and  "  E  "  strong 
potassium  hydroxide  for  absorbing  the  carbon  dioxide.  When  gas 
ceases  to  be  absorbed  in  "E"  "g"  and  uh"  are  connected  and  air  is 


FIG.  55. 

drawn  through  the  apparatus  by  means  of  the  aspirator  "H,"  the 
screw  clip  "a"  being  opened  slightly  at  the  same  time.  "F"  is  packed 
with  small  pieces  of  potassium  hydroxide  and  "G"  with  calcium 
chloride.  About  12.50  c.c.  of  air  aspirated  through  the  apparatus 
will  suffice  to  remove  all  traces  of  carbon  dioxide  from  the  beer. 
The  flame  is  then  taken  from  under  the  flask  "  A, "  "  E  "  is  disconnected 
and  in  due  course  weighed.  The  difference  in  weight  before  and  after 
the  experiment  is  the  amount  of  carbon  dioxide  absorbed. 

If  it  is  desired  to  estimate  the  amount  of  carbon  dioxide  in  a  bottled 
beer  the  cork  is  pierced  with  a  pointed  hollow  tube  carrying  a  tap. 
The  exit  from  the  tap  is  connected  with  "C"  by  the  rubber  joint  "m" 


BEER. 

and  the  gas  allowed  to  slowly  escape.  The  bottle,  still  attached  to  "m," 
is  then  placed  in  a  water-bath  which  is  raised  to  b.  p.  When  gas 
ceases  to  be  given  off  the  bottle  of  beer  is  removed,  the  tube  "C" 
connected  with  the  condenser  and  the  beer  when  cold  placed  in  "A." 
The  contents  of  the  flask  "A"  are  boiled  and  air  aspirated  through  the 
apparatus  as  before. 

A.  O.  A.  C.  PROCESS  (Bulletin  107,  Bur.  of  Chem.,  U.  S.  Dept.  of 
Agric.): 

Bottled  Beers. — Pierce  the  cork  with  a  champagne  tap.  (Cramp- 
ton  found  it  advantageous  to  re-grind  the  cocks  and  ream  off  the 


FIG.  56. — Crampton  and  Trescot;  Bulletin  107,  Bur.  of  Chem.  U.  S.  Dept.  Agric. 

thread.)  The  bottle  thus  tapped  is  connected  with  the  absorption 
apparatus  shown  in  Fig.  56,  devised  by  Crampton  and  Trescot.  The 
can  containing  the  bottle  holds  a  convenient  amount  of  cold  water. 
The  tap  is  opened  so  as  to  allow  the  gas  to  escape  slowly,  and  when  the 
flow  ceases,  the  water  is  heated  slowly  to  about  80°,  shaking  the  bottle 
from  time  to  time  during  about  30  minutes  while  this  temperature  is 
maintained.  The  bottle  is  then  disconnected  and  air  under  the  usual 
precautions  drawn  through  the  apparatus.  The  increase  in  weight 
of  the  absorption  tube  gives  the  amount  of  carbon  dioxide.  The  contents 
of  the  bottle  are  either  weighed  or  measured  to  give  the  necessary  data 
for  calculation.  Bottles  carrying  patent  stoppers  can  sometimes 
be  adapted  to  this  method  by  substituting  quickly  a  rubber  stopper 
fitted  with  a  suitable  stopcock  tube.  When  this  cannot  be  done,  the 
method  given  in  the  next  paragraph  must  be  employed. 


l6o  MALT   AND    MALT    LIQUORS. 

Bulk  Beers. — A  round-bottom  flask,  about  700  c.c.  capacity,  is 
provided  with  a  rubber  stopper  carrying  two  stopcock  tubes,  each  bent 
at  right  angles,  one  tube  passing  to  the  bottom  of  the  flask,  the  other 
terminating  just  below  the  stopper.  A  partial  vacuum  is  produced 
in  the  flask  which  is  then  weighed.  The  end  of  one  of  the  stopcock 
tubes  is  then  dipped  below  the  surface  of  the  sample  and  about  300 
c.c.  allowed  to  enter  the  flask,  which  is  then  weighed,  and  the  procedure 
for  bottled  samples  followed.  It  is  recommended  as  a  better  manip- 
ulation to  attach  to  one  of  the  stopcock  tubes,  by  means  of  a  rubber 
tube,  a  champagne  tap  that  has  been  screwed  into  the  cask.  Some- 
what better  results  may  be  obtained  by  placing  a  reflux  condenser 
between  the  flask  and  absorption  apparatus  and  heating  the  flask  until 
the  contents  boil. 

The  Mineral  Constituents  of  Beers. — The  total  ash  of  a  beer 
may  be  estimated  by  evaporating  50  c.c.  of  the  sample  to  dryness 
in  a  large  platinum  crucible,  and  cautiously  igniting  at  a  low  red  heat 
in  a  muffle.  An  estimation  of  certain  of  the  ash  constituents  is  some- 
times useful  in  determining  if  a  beer  is  correctly  described  as  the  prod- 
uct of  a  certain  brewery.  For  example,  a  brand  of  beer  may  be 
brewed  to  contain  certain  proportions  of  gypsum  or  chlorides.  An 
estimation  of  these  constituents  would  afford  material  evidence  in 
detecting  a  case  of  fraudulent  substitution. 

In  instances  where  the  addition  of  large  quantities  of  sodium  chloride 
is  suspected  a  quantity  of  the  beer  (50  c.c.)  should  be  evaporated  to 
dryness  in  the  presence  of  sodium  carbonate  and  ashed  in  a  muffle 
at  as  low  a  heat  as  possible.  The  total  chlorine  in  the  ash  is  estimated 
gravimetrically.  Race  (J.Soc.  Chem.  Ind.,  1908,  27,  548)  recommends 
evaporating  50  c.c.  of  the  beer  with  0.5  grm.  of  barium  carbonate 
and  subsequently  igniting  to  a  black  ash.  The  ash  is  extracted 
with  hot  water,  filtered,  and  titrated  with  silver  nitrate  in  the  usual 
manner. 

Another  volume  of  50  c.c.  of  the  beer  is  evaporated  to  dryness, 
moistened  with  sulphuric  acid  and  ashed.  The  potassium  is  esti- 
mated as  chloroplatinate  and  the  sodium  by  difference.  From  these 
data  and  the  chlorine  the  amount  of  sodium  chloride  present  in  the 
beer  may  be  calculated.  Beer  may,  under  English  regulations,  con- 
tain 50  grains  of  sodium  chloride  per  imperial  gallon,  (41.5  grains 
per  U.  S.  gallon)  this  amount  being  derived  from  the  treatment  of  the 
mashing  liquor  and  from  the  malt  and  malt  substitutes  used. 


BEER.  l6l 

Sulphates. — 50  c.c.  of  the  beer  are  evaporated  to  dryness  in  the 
presence  of  a  small  quantity  of  sodium  hydroxide,  the  mass  ashed  and 
the  sulphates  estimated  in  the  usual  manner.  If  the  beer  is  burnt  by 
itself  loss  of  sulphuric  anhydride  occurs  owing  to  the  interaction  be- 
tween acid  phosphates  and  the  sulphates. 

The  question  of  whether  a  beer  is  made  from  an  all-malt  grist  or  part 
malt  and  part  substitute  is  often  asked.  It  may  be  asserted  that  with 
a  few  exceptions  nearly  all  brewers  use  substitutes.  In  the  United 
Kingdom  the  malt  and  hops  comprise  83%  of  the  solid  materials 
used  in  brewing,  the  remaining  17%  including  unmalted  corn,  malt 
substitutes,  and  sugars.  The  nature  and  proportion  of  nitrogenous 
matter  has  been  suggested  as  a  means  of  detecting  substitutes,  but 
when  the  varying  composition  of  malt  is  borne  in  mind  it  will  be  realised 
that  no  safe  conclusion  can  be  drawn  from  such  data.  The  fact  that 
the  amount  of  phosphoric  acid  is  higher  in  an  all-malt  beer  than  in  one 
brewed  with  substitutes  has  been  proposed  as  a  means  of  detecting  sub- 
stitutes. The  amount  of  phosphates,  however,  differs  in  malt,  also  the 
quantity  taken  up  in  the  development  of  the  yeast  is  not  constant. 
Hence  the  evidence  afforded  by  this  estimation  is  only  diagnostic  and 
and  not  conclusive. 

Detection  of  Bitter  Substances  in  Beer. — Very  elaborate  proc- 
esses have  been  devised  by  Dragendorff,  Wittstein  and  others  for  detect- 
ing the  presence  of  substances  which  might  possibly  be  used  for  impart- 
ing a  bitter  taste  to  beer,  but  it  will  be  sufficient  to  describe  here  the 
method  of  searching  for  the  more  commonly  used  "hopsurrogates," 
and  certain  objectionable  substances  the  occasional  employment  of 
which  is  suspected. 

A.  C.  Chapman  (Analyst,  1900,  25,  35)  has  devised  a  method  for  dis- 
tinguishing between  hops  and  quassia,  which  is  based  upon  the  pro- 
duction of  valeric  acid  when  the  ether  extract  of  hops  is  oxidised  with 
an  alkaline  solution  of  potassium  permanganate.  500  c.c.  of  the 
beer  are  evaporated  on  the  water-bath  with  the  addition  towards  the 
end  of  the  operation  of  some  ignited  sand,  the  mass  being  constantly 
stirred  to  prevent  it  from  adhering  to  the  surface  of  the  dish.  The 
residue  is  dried  in  an  air  oven,  finely  powdered  and  extracted  in  a  bottle 
with  ether.  The  ether  is  removed  from  the  extract  and  the  residual 
matter  oxidised  by  the  careful  addition  of  an  alkaline  solution  of  potas- 
sium permanganate  containing  40  grm.  of  permanganate  and  10  grm. 
of  potassium  hydroxide  in  1000  c.c.  This  solution  should  be  added 
Vol.  I— IT 


162 


MALT    AND    MALT    LIQUORS. 


in  small  quantities  at  a  time,  the  flask  being  vigorously  shaken  and  if 
necessary  warmed.  When  the  permanganate  ceases  to  be  readily  re- 
duced, a  few  drops  of  a  hot  solution  of  oxalic  acid  are  added  to  complete 
the  reduction,  and  the  colourless  liquid  filtered  from  the  manganese 
oxides  into  a  glass  dish,  in  which  it  is  evaporated  to  dryness.  The  dry 
residue  is  then  acidified  with  dilute  sulphuric  acid,  when  the  odour 
of  valeric  acid  in  the  case  of  the  hop-bittered  liquid  becomes  at  once 
apparent,  being  rather  accentuated  by  the  carbon  dioxide  liberated 
at  the  same  time  from  the  potassium  carbonate  formed  during  the  oxi- 
dation. The  smell  observed  is  not  that  of  pure  valeric  acid,  but  of 
valeric  acid  plus  some  other  odorous  compound,  which  serves  to 
render  it  more  characteristic.  In  the  case  of  the  quassia  the  liberated 
acid  is  chiefly  acetic.  Old  hops  respond  as  readily  to  this  test  as  new 
hops.  Camomile  extract  behaves  in  a  similar  manner  to  hops,  but 
chiretta  yields  no  valeric  acid. 

OUTLINE  PROCESS  FOR  THE  DETECTION  OF  BITTER 
PRINCIPLES  IN  BEER. 


1000  c.c.  of  beer  is  evaporated  to  half  its  bulk  and  precipitated  boiling  with  neutral  lead 
acetate,  the  liquid  boiled  for  fifteen  minutes  and  filtered  hot.  If  any  precipitate  separates 
cooling,  the  liquid  is  again  filtered. 


bitter,      car- 
amel -  bitter. 
ephelic     acid 
(from      chir- 
etta),    phos- 
phates, albu- 
menous  mat- 
ters, etc.,  etc. 

Filtrate.    The   lead   is  removed    by  hydrogen  sulphide  and    the    filtered 
liquid  concentrated  to  about  150  c.c.  and  tasted.     If  any  bitter  taste  is 
perceived,  the  liquid  is  then  slightly  acidulated  with  dilute  sulphuric  acid, 
and  shaken  repeatedly  with  chloroform. 

Chloroform  layer,  on  evap- 
oration,   leaves    a    bitter 
extract  in  the  case  of  gen- 
tian, calumba,  quassia,  and 
old  hops  (only  slightly  or 
doubtfully   bitter    in    the 
a)  .    The  residue  is  dissolved 
ol,  hot  water  added,  and  the 
;ated  with  ammoniacal  basic 
d  filtered. 

Aqueous  liquid  is  shaken  with 

ether. 

Ethereal  layer  leaves  a  bitter 
residue  in  the  case  of  chiretta, 
gentian,  or  calumba.    It  is  dis- 
solved in  a  little  alcohol,  hot 
water  added,  and  the  hot  solu- 
tion treated  with  ammoniacal 
basic  lead  acetate  and  filtered. 

Aqueous    liq- 
uid,   if     still 
bitter      is 
rendered  al- 
kaline     and 
shaken  with 
ether  -  chlor- 
oform.     A 
bitter       ex- 
tract may  be 
due    to    ber- 
berine     (cal- 
umba)       or 
strychnine. 

The   aqueous 
liquid,  sepa- 
rated    from 
the       ether- 
chloroform, 
may  contain 
caramel  -  bit- 
ter or  choline 
(somewhat 
bitter). 

case  of  chiretl 
in  a  little  alcoh 
hot  solution  tr< 
lead  acetate  an 

Precipitate     contains     the  !  Filtrate  is  boil- 
bitters  of  old  hops,  gentian,  j    ed  to  remove 
and    caramel.    It    is  sus-  j    ammonia,  and 
pended  in  water,  decom-  i    treated  with  a 
posed  by  hydrogen    sul-  j    slight      excess 
phide,  and    the    solution  i    of       sulphuric 
agitated  chloroform.                acid       filtered 
1    and      tasted. 

Precipitate     is    Filtrate     is 
treated    with      treated    with 
water  and  de-      a    slight    ex- 
composed  by      cess  of  dilute 
hydrogen  sul-      sulphuric 
Ehide.    The      acid,    filtered 
Itered  liquid      and  tasted.  A 
is  bitter  in      bitter      taste 
presence     o  f      indicates  col- 
gentian,                umba  or  Chir- 
etta,   which 
may  be  re-ex- 
tracted   with 
ether  and  fur- 
ther     exam- 
ined. 

Chloroform 
Layer  is  ex- 
amined    by 
special  tests  ! 
for     gentian 
and  old  hop- 
bitter. 

|    If  bitter,  it  is 
Aqueous      agitated   with 
1  i  q  u  i  d  j    chloroform, 
contains  1    and    the    resi- 
traces     of  1    due  examined 
caramel-  '    for       calumba 
bitter.               and  quassia. 

' 

BEER.  163 

This  method  is  applicable  to  the  examination  of  hop-bitter  prepara- 
tions (of  a  medicinal  character),  hop  extracts,  and  similar  products. 
It  furnishes  additional  evidence  in  the  case  of  fermented  beverages 
which  have  been  examined  according  to  the  systematic  schemes  in 
vogue,  and  which  have  yielded  results  of  an  uncertain  nature. 

Preservatives  in  Beer. — The  most  commonly  occuring  preserva- 
tive is  sulphurous  acid,  usually  as  a  sulphite  or,  rarely,  in  the  free  state. 
Salicylic  acid  is  also  used,  often  in  association  with  a  sulphite.  Fluo- 
rides are  occasionally  found  in  continental  beers. 

Salicylic  Acid. — The  following  process  devised  by  F.  T.  Harry  and 
W.  R.  Mummery  (Analyst,  1905,  30, 124-127)  gives  satisfactory  results: 

100  c.c.  of  the  beer  are  placed  in  a  graduated  200  c.c.  flask  made 
alkaline  with  5  c.c.  normal  sodium  hydroxide  and  the  alcohol  driven 
off  at  a  temperature  just  below  the  b.  p.  After  cooling  5  c.c.  of 
normal  hydrochloric  acid  are  added  and  20  c.c.  of  basic  lead  acetate 
solution;  the  mixture  is  then  made  alkaline  with  about  20  c.c.  of  N/i 
sodium  hydroxide  and  made  up  to  200  c.c.  At  this  stage  the  solution 
may  be  raised  to  boiling  and  allowed  to  cool  before  filtering,  but  this  may 
be  omitted  if  thought  advisable.  100  c.c.  of  the  filtrate  are  acidified 
with  hydrochloric  acid,  a  precipitate  of  lead  chloride  being  thrown 
down  and  filtered  off.  The  filtrate  is  extracted  with  ether  three  times, 
the  ether  distilled  off  and  the  salicylic  acid  dissolved  in  a  small  quantity 
of  dilute  alcohol  and  made  up  to  100  c.c.  The  salicylic  acid  is  estimated 
colorimetrically  in  ordinary  50  c.c.  Nessler  tubes  with  very  weak  ferric 
chloride  solution  which  should  be  made  up  freshly  when  required.  The 
standard  salicylic  solution  is  o.oi  %  strength.  The  tendency  which  beers 
have  to  emulsify  when  shaken  with  ether  is  obviated  by  this  process. 

Sulphites. — 5  c.c.  of  phosphoric  acid  are  added  to  300  c.c.  of  beer, 
the  mixture  distilled  and  N/ioo  iodine  solution  run  in  until  there  is  a 
permanent  yellow  color.  The  excess  of  iodine  is  determined  by  N/ 100 
sodium  thiosulphate  solution  in  the  usual  manner.  One  c.c.  N/ioo 
iodine  is  equivalent  to  0.00032  grm.  SO2. 

Fluorides. — 100  c.c.  of  the  beer  are  made  slightly  alkaline  with  am- 
monium carbonate,  boiled  and  2  or  3  c.c.  of  10%  calcium  chloride 
solution  added;  again  boiled  for  five  minutes,  the  precipitate  filtered, 
washed  and  dried.  The  dried  precipitate  is  detached  from  the  paper, 
placed  in  a  platinum  crucible  and  ignited,  then  powdered  with  a  small 
pestle,  moistened  with  2  or  3  drops  of  water  and  i  c.c.  of  strong  sulphuric 
acid.  The  crucible  is  covered  with  a  watch-glass,  the  surface  of  which 


164  MALT   AND    MALT    LIQUORS. 

is  waxed  and  marked  with  a  style.  The  crucible  and  its  contents  are 
gently  warmed  on  the  water-bath,  the  wax  on  the  cover-glass  removed 
and  any  etching  on  the  glass  surface  noted.  To  prevent  the  wax 
melting  during  the  process,  the  watch-glass  is  covered  with  a  larger 
glass  on  which  pieces  of  ice  are  placed. 

Saccharin. — The  addition  of  saccharin  is -forbidden  in  most  coun- 
tries. Allen  (Analyst,  1888,  13,  105)  devised  the  following  method 
for  its  detection: 

The  beer  is  concentrated  to  1/3  its  bulk,  and  if  not  acid,  is  rendered 
so  by  the  addition  of  a  little  pure  phosphoric  acid.  The  liquid  is  then 
shaken  with  ether,  the  ether  decanted  and  evaporated,  and  the  residue 
burned  off  after  being  mixed  with  sodium  carbonate  and  a  little  sodium 
nitrate.  The  sulphur  in  the  saccharine  is  thus  converted  into  sulphate, 
and  can  be  estimated  in  the  usual  way.  The  weight  of  barium  sul- 
phate multiplied  by  0.785  gives  the  weight  of  saccharin.  Of  course, 
all  the  reagents  must  be  free  from  sulphates. 

The  Stability  of  Finished  Beers. — Useful  information  as  to  the 
keeping  qualities  of  beers  and  their  suitability  for  certain  purposes, 
such  as  bottling,  exporting  to  hot  countries,  etc.,  may  be  obtained  from 
the  "  forcing  test."  (For  a  full  description  of  this  test  see  Matthews  and 
Lott,  The  Microscope  in  the  Brewery,  2d  ed.,  page  128.)  The  samples 
of  beer  are  placed  in  carefully  cleaned  conical  flasks  fitted  with  rubber 
stoppers  carrying  tubes  which  dip  down  into  a  receptacle  containing 
mercury.  The  flasks  are  placed  on  the  outside  of  a  large  metal  water- 
bath,  maintained  at  a  temperature  of  80°  to  85°  F.,  or  better  in  an  in- 
cubator, for  certain  specified  periods  which  are  regulated  by  the  "trade 
expectations"  of  the  beers  under  examination.  The  apparent  gravity, 
acidity,  flavour,  odour  and  condition  are  recorded  before  and  after  the 
test  and  the  sediment  which  is  formed  carefully  examined  for  wild 
yeasts  and  bacteria. 

Beers  for  export  purposes  and  stock  ales  and  stouts  should  be  per- 
fectly sound  and  the  sediment  free  from  bacteria  after  4  weeks'  dura- 
tion of  the  test.  India  pale  ales  should  stand  three  weeks;  light  bot- 
tling ales  and  stouts  a  fortnight;  and  running  beers,  such  as  mild  ale  and 
porter,  a  week.  The  loss  in  gravity  during  the  forcing  test  is  an  indica- 
tion as  to  the  rapidity  with  which  a  beer  will  get  into  condition  in  bottle. 
It  is  not  possible  to  discuss  the  test  fully  in  the  present  article,  but  if 
intelligently  used  it  affords  information  of  considerable  diagnostic  value 
to  the  brewer. 


WINES  AND  POTABLE  SPIRITS. 


BY  G.  C.  JONES,  F.  I.  C.,  A.  C.  S.  I. 

WINES. 

Many  distinguished  chemists  have  devoted  attention  to  the  analysis 
of  wines  and  new  methods  or  modifications  of  old  ones  are  proposed 
annually.  Since,  however,  few  of  the  estimations  are  absolute,  new 
methods,  even  if  good,  are  very  cautiously  received  by  continental 
chemists,  who  hold  that  it  is  more  important  to  obtain  numbers  strictly 
comparable  with  those  previously  accumulated  than  to  increase  slightly 
the  accuracy  of  a  single  determination.  In  these  circumstances,  the 
reader  has  a  right  to  expect  in  a  work  of  this  kind  a  description  of 
official  methods  of  analysis,  and  with  this  in  mind  the  writer  has  tried 
to  steer  a  middle  course  between  rival  official  methods,  and,  where  the 
estimation  is  one  which  may  be  seriously  influenced  by  departure  from 
standard  conditions,  to  point  out  difference  in  the  official  methods  of 
different  countries.  Frequent  reference  is  made  in  this  section  to 
Bulletin  No.  59,  United  States  Department  of  Agriculture  (Division  of 
Chemistry)  which  wrill  for  the  sake  of  brevity  be  cited  by  the  author's 
name  (Bigelow).  The  methods  described  by  Bigelow  differ  very  little 
from  the  German  methods,  which  may  be  found  described  in  great  detail 
in  K.  Windisch's  Chemische  Untersuchung  des  Weines  (Berlin,  1896). 
A  German  imperial  decree  of  1896  was  very  fully  abstracted  in 
/.  Soc.  Chem.  2nd.,  1898,  17,  277,  and  will  be  found  to  contain  an 
amount  of  detail  concerning  analytical  methods  which  is  scarcely 
justifiable  in  this  work. 

The  following  determinations  are  usually  made: 

Specific  gravity. 

Alcohol. 

Glycerol. 

Extract. 

Ash. 

Acidity  (volatile  and  fixed). 

Sugar. 

Potassium  sulphate. 

Sulphurous  acid. 

165 


1 66  WINES    AND    POTABLE    SPIRITS. 

In  addition  to  these  it  is  sometimes  necessary  to  estimate  tannin  and 
to  look  for  saccharin,  salicylic  acid  and  other  preservatives.  It  is  con- 
venient to  return  all  results  as  grm.  per  100  c.c.  of  wine.  The  deter- 
mination of  the  sp.  gr.  and  estimation  of  alcohol  do  not  need  description 
here. 

Glycerol. — The  German  official  methods  are  as  follows: 

a.  In  wines  containing  less  than  2  grm.  of  sugar  per  100  c.c.,  100  c.c. 
are  evaporated  to  10  c.c.  in  porcelain  on  the  water-bath,  and  the  resi- 
due mixed  with  i  grm.  of  quartz  sand  and,  for  each  grm.  of  extract 
present    1.5   to   2   c.c.   of   milk   of   lime    (40%   calcium   hydroxide). 
Evaporation  is  continued  almost  to  dryness  and  then  5  c.c.  of  96% 
alcohol  added.     The  matter  which  adheres  to  the  sides  of  the  dish 
is  loosened  with  a  spatula  and  reduced  by  a  small  pestle  to  a  thin 
paste,  further  small  quantities  of  96%  alcohol  being  added  as  required. 
The  mixture  is  heated  on  the  water-bath,  with  constant  stirring,  until 
it  begins  to  boil,  when  the  liquid  portion  is  decanted  into  a  100  c.c. 
flask.     The.  residue  in  the  dish  is  repeatedly  extracted  with  10  c.c. 
portions  of  96%  alcohol,  which  are  decanted  into  the  100  c.c.  flask, 
until   this   contains   about   95   c.c.     The  contents   of  the   flask   are 
cooled  to  15°  and  96%  alcohol  added  until  the  volume  reaches  100 
c.c.     The  liquid  is  filtered  and  90  c.c.  evaporated  in  porcelain  on  a 
water-bath,  avoiding  vigorous  boiling  of   the  alcohol.     The  residue 
is  taken  up  with  a  small  quantity  of  absolute  alcohol  which  is  poured 
into  a  stoppered  cylinder,  and  the  dish  washed  out  with  more  alcohol 
until  the  cylinder  contains  15  c.c.     Three  separate  portions  of  absolute 
ether,  each  of  7.5  c.c.  are  now  added  to  the  contents  of  the  cylinder, 
which  is  vigorously  shaken  after  each  addition.     When  the  liquid  ap- 
pears quite  clear,  it  is  poured  into  a  tared  glass  dish,  the  cylinder 
rinsed  with  5  c.c.  of  alcohol-ether  mixture  (2:3)   and  the  rinsings 
added  to  the  dish,  which  is  then  placed  on  a  hot  water-bath,  which, 
however,  must  not  be  so  hot  as  to  cause  actual  boiling  of  the  liquid. 
The  syrupy  residue  is  dried  in  the  steam  oven  for  an  hour,  cooled  in  a 
desiccator  and  weighed. 

b.  In  wines  containing  more  than  2  grm.  of  sugar  per  100  c.c.,  50  c.c. 
are  warmed  in  a  capacious  flask  on  the  water-bath,  and  mixed  with  i 
grm.  of  quartz  sand  and  small  quantities  of  milk  of  lime  added  till  the 
colour,  at  first  dark,  again  becomes  pale  and  the  liquid  assumes  a 
characteristic  alkaline  odour.     After  cooling,  100  c.c.  of  96%  alcohol 
is  added,  the  precipitate  allowed  to  subside,  and  the  liquid  filtered, 


WINES.  167 

the  precipitate  and  filter  being  washed  with  96%  alcohol.  The 
filtrate  is  then  treated  as  in  process  (a). 

The  above  troublesome  process  is  likely  to  remain  official  until  either 
an  exact  method  is  evolved  or  a  simpler  method  devised  which  will 
give  results  strictly  comparable  with  those  obtained  by  the  ether-alcohol 
method.  Windisch  (loc.  cit.,  80-82)  gives  a  complete  set  of  references 
to  the  literature  of  the  subject  up  to  1895.  Since  then  the  most  impor- 
tant communication  has  been  that  of  Trillat  (Compt.  rend.,  1902, 
I35>  9°3)  wno  recommends  the  following  simple  method,  which  has 
some  followers  in  France. 

50  c.c.  of  wine  are  evaporated  to  one-third  bulk  in  a  silver  or  nickel 
dish  at  70°,  5  grm.  of  animal  charcoal  is  added,  and  evaporation  con- 
tinued to  dryness,  when  the  residue  is  mixed  in  a  mortar  with  5  grm. 
of  quicklime,  extracted  twice  by  thorough  shaking  in  a  flask  with  30  c.c. 
of  dry  ethyl  acetate  (free  from  alcohol)  and  the  extract  filtered,  evapor- 
ated on  the  water-bath,  and  dried  in  an  oven  at  60°  to  constant  weight. 

Glycerol  itself  is  none  too  easily  extracted  by  ethyl  acetate,  and 
in  consequence  other  workers  (Rocques,  Ann.  Chim.  anal.,  1905,  10, 
306,  and  Billon,  Rev.  intern,  falsif.,  1906,  19,  57)  have  improved  on 
Trillat's  method  until  it  is  quite  as  complicated  as  the  ether-alcohol 
method. 

An  entirely  original  method  is  that  of  Laborde  (/.  Pharw.,  1895, 
6,  i,  568,  and  Ann.  Chim.  anal.,  1899,  4,  76  and  no,  and  1905,  10, 
340).  It  is  based  on  the  fact  that  at  150°  to  200°  glycerol  is  quantita- 
tively decomposed  by  sulphuric  acid  with  the  liberation  of  the  whole 
of  the  carbon  which  Laborde  weighs  as  such. 

As  one  of  the  newer  methods  may  obtain  official  sanction  if  experience 
shows  it  to  be  quicker  and  to  give  results  comparable  with  those  ob- 
tained by  the  present  official  methods,  it  has  been  thought  u  orth  while 
to  bring  Windisch's  list  of  references  up  to  date,  following  his  classifi- 
cation. In  addition  to  the  methods  already  referred  to,  the  following 
have  been  described  since  1895: 

1 .  Modifications  of  the  ether-alcohol  method. 

Fabris,  UOrosi,    1897,    20,  260.     Details  for  manipulation  of 

sweet  wines  only. 

Guglielmetti  and  Copetti,  Ann.  Chim.  anal.,  1904,  9,  n. 

2.  Oxidation  Methods. 

Depending  on  the  use  of   potassium  permanganate   in   acid 


l68  WINES    AND    POTABLE    SPIRITS. 

solution.      Mancuso-Lima  and   Scarlata,  Staz.  Sper.  Agrar., 
1895,  28,  206. 

Depending  on   the   use   of  chromic   acid.     Bordas   and   de 
Raczkowski,  Compt.  rend.,  1896,  123,  1021. 

3 .  By  esterification. 

As  triacetin.     Bottinger,  Chem.  Zeit.,  1897,  21,  659. 

4.  By    steam-distillation    under   reduced    pressure.     Bordas    and 
de  Raczkowski,  Compt.  rend.,  1897,  124,  240. 

5 .  By  conversion  into  isopropyl-iodide  by  Zeisel's  method,  weigh- 
ing as  silver  iodide. 

Zeisel  and  Fanto,  Zeit.  anal.  Chem.,  1903,  42,  549. 
(See  under  Glycerol,  Vol.  II.) 

Extract. — In  sweet  wines,  sugar  forms  an  important  part  of  the 
solids,  the  extract  can  be  ascertained  with  fair  accuracy  from  the 
sp.  gr.  of  the  original  wine  and  that  of  the  alcoholic  distillate,  on 
the  assumptions,  not  very  inaccurate,  that  a  solution  of  wine  solids, 
containing  10  grm.  per  100  c.c.,  has  a  sp.  gr.  of  1.0386  and  that  the 
excess  gravity  over  water  (=  i)  is  proportional  to  the  amount  of  extract 
present.  If  s  be  the  sp.  gr.  of  the  wine,  and  s'  the  sp.  gr.  of  the  alcoholic 
distillate  diluted  to  a  bulk  equal  to  that  of  the  wine  from  which  it 
is  derived,  then  the  extract,  x,  in  grm.  per  TOO  c.c.,  is  given  by: 
#  =  (s  — s')  -T-  0.00386. 

If  the  extract  so  determined  is  less  than  5  %  a  direct  estima- 
tion is  advisable,  as  the  factor  0.00386  is  much  less  accurate  for  the 
other  wine  solids  than  for  the  sugar,  which  predominates  only  in  wines 
of  relatively  high  extract  content.  To  this  end  25  c.c.  (or  50  c.c.  if  the 
extract  is  below  2.5  %)  are  evaporated  to  a  thick  syrup  in  a  3 -in.  flat- 
bottomed  platinum  dish,  transferred  without  delay  from  the  water- 
bath  to  a  steam  oven,  and  after  2  hours,  cooled  in  a  desiccator  and 
weighed.  If  the  extract  much  exceeds  5  %  it  is  better  to  be  satisfied 
with  the  indirect  estimation  from  the  sp.  gr.,  since  it  is  practically  im- 
possible to  dry  such  extracts  under  the  above  conditions.  The  direct  es- 
timation in  any  case  is  purely  empirical,  the  result  depending  on  the 
size  and  thickness  of  the  dish  and  the  size,  shape  and  manner  of  ventila- 
tion of  the  steam  oven;  all  these  are  rigidly  defined  by  continental 
workers. 

In  Germany  no  direct  estimation  is  made  if  the  extract  exceeds 
4%;  if  it  is  less  than  3%  50  c.c.  are  evaporated,  while  if  it  is  between 


WINES.  169 

3  and  4^0  so  much  is  evaporated  as  will  leave  not  more  than  1.5  grm. 

The  official  United  States  directions  are  to  take  50  c.c.  for  dry  wines 
and  25  c.c.  for  sweet  wines,  with  the  reservation  that  when  the  extract 
exceeds  6%  no  direct  estimation  is  to  be  attempted. 

In  France  extract  is  estimated  by  evaporation  in  a  dish  as  described, 
followed  by  6  or  7  hours  heating  on  the  water-bath.  This  method 
gives  lower  results,  since  most  of  the  glycerol  is  expelled,  whereas  during 
2  hours  in  the  oven  little  is  lost. 

Ash. — The  residue  from  the  estimation  of  extract,  or  from  the 
evaporation  of  25  c.c.  of  the  wine  if  the  extract  was  not  directly  deter- 
mined, is  cautiously  charred,  and  repeatedly  extracted  with  small 
portions  of  hot  water,  which  are  then  decanted  through  a  small  ashless 
filter.  The  filter  is  then  returned  to  the  dish,  dried  and  ashed.  When 
the  ash  is  quite  white,  the  filtrate  is  added  to  the  contents  of  the  dish, 
evaporated  to  dryness,  moistened  with  ammonium  carbonate  solution, 
heated  to  a  dull  redness,  cooled  in  a  desiccator  and  weighed. 

Total  Acid. — 25  c.c.  of  the  wine  are  quickly  heated  to  incipient 
boiling  and  quickly  titrated  with  N/2  sodium  hydroxide,  using  litmus 
paper  as  indicator.  The  alkali  should  be  standardised  against  25  c.c. 
of  a  N/io  solution  of  an  organic  acid  under  the  same  conditions  and 
with  the  same  indicator.  The  object  of  heating  is  not  only  to  expel 
carbon  dioxide,  but  to  reduce  the  amphoteric  reaction  of  the  wine  when 
nearing  neutralisation.  If  the  liquid  be  heated  quickly  and  only  until 
it  begins  to  boil  no  appreciable  loss  of  acetic  acid  will  result.  The  use 
of  N  2  alkali  reduces  the  bulk  of  cold  liquid  to  be  added  and  hastens 
the  titration;  the  reading  is  smaller  than  with  N/io  alkali,  but  is 
sufficiently  large.  The  acidity  is  usually  calculated  as  tartaric  acid, 
though  in  fact  free  tartaric  acid  is  seldom  present  in  more  than  traces. 

In  France  the  convention  is  to  calculate  the  acidity  as  equal  to  so 
many  grm.  of  sulphuric  acid  per  1000  c.c.  and  it  is  important  to 
bear  this  definition  of  acidity  in  mind  when  referring  to  French 
standards. 

In  the  United  States  official  methods  25  c.c.  of  wine  are,  after  shaking 
to  expel  carbon  dioxide,  titrated  cold  with  N/io  sodium  hydroxide, 
using  as  indicator  litmus  solution,  or  in  the  case  of  red  wines  the  change 
of  the  wine  colour  to  violet. 

Volatile  Acid. — 50  c.c.  of  the  wine  are  distilled  in  a  current  of  steam 
free  from  carbon  dioxide.  A  little  tannin  added  to  the  wine  prevents 
foaming  and  is  preferable  to  the  use  of  a  spray  trap.  The  wine  is 


170  WINES   AND    POTABLE    SPIRITS. 

directly  distilled  until  the  volume  is  reduced  to  about  25  c.c.;  steam 
is  turned  on  and  the  flame  under  the  flask  so  adjusted  that  the  volume 
remains  about  25  c.c.  while  a  total  distillate  of  200  c.c.  is  collected. 
This  is  titrated  with  N/ 10  sodium  hydroxide,  using  phenolphthalein  as 
indicator,  and  the  acidity  calculated  as  acetic  acid. 

Fixed  Acid. — This  is  estimated  by  difference.  Since  the  total  acid 
was  reckoned  as  tartaric  and  the  volatile  as  acetic  acid,  the  fixed  acid 
in  terms  of  tartaric  acid  is  found  by  subtracting  1.25  times  the  volatile 
acid  from  the  total  acid. 

It  is  not  permissible  to  estimate  the  fixed  acids  directly  by  evaporating 
to  dryness,  subsequently  titrating  the  redissolved  residue,  since  fixed 
acids  may  be  destroyed  during  the  last  stages  of  the  evaporation. 
On  the  other  hand,  Windisch  (Zeit.  Nahr.  Genussm.,  1905,  9,  70)  has 
shown  that  the  above-described  method  for  the  estimation  of  volatile 
acids  is  not  quite  satisfactory  on  account  of  the  partial  volatility  of  lactic 
acid,  which  may  be  the  chief  acid  present,  and  he  suggests  the  following 
method.  25  c.c.  of  the  wine  are  evaporated  to  about  3  c.c.,  25  c.c.  of 
hot  water  added,  and  the  liquid  again  evaporated  to  3  c.c.,  and  this 
process  repeated  once  more.  The  residue  is  diluted  and  titrated 
with  standard  alkali.  From  the  result  is  calculated  the  fixed  acid 
and  from  this  and  the  total  acid  the  amount  of  volatile  acid  may  be 
obtained  indirectly. 

Reducing  sugar  is  estimated  with  Fehling's  solution.  Two  hundred 
c.c.  of  wine  are  neutralised  with  sodium  hydroxide  and  evaporated  to 
about  50  c.c.,  cooled,  transferred  to  a  200  c.c.  flask  and  diluted  to  about 
160  c.c.  Basic  lead  acetate  solution  (20  c.c.)  is  added  and  the  con- 
tents of  the  flask  made  up  to  the  200  c.c.  mark  with  water.  The  mix- 
ture is  shaken  and  filtered.  To  100  c.c.  of  the  filtrate,  10  c.c.  of  a 
saturated  solution  of  sodium  sulphate  are  added,  the  mixture  shaken 
and  filtered.  The  filtrate,  a  volume  of  n  c.c.  of  which  corresponds  to 
10  c.c.  of  wine,  serves  for  the  estimation  of  reducing  sugars.  This  may 
be  carried  out  as  described  in  the  " Sugars"  section  of  this  work.  In 
Germany  and  the  United  States,  the  gravimetric  method  is  officially 
practised,  25  c.c.  of  the  above  filtrate  being  taken  for  the  test.  In 
Germany  50  c.c.  of  Fehling's  solution  and  25  c.c.  of  water  are  taken, 
the  precipitate  reduced  and  weighed  as  copper  in  a  Soxhlet  tube,  and 
calculated  as  invert  sugar  by  means  of  Wein's  tables.  In  the  United 
States  60  c.c.  of  Fehling's  solution  and  60  c.c.  of  water  are  taken  and 
the  precipitate  oxidised  to  CuO  in  a  Gooch  crucible,  the  result  being 


WINES.  171 

calculated  from  Allihn's  tables  as  dextrose.  The  volumetric  method, 
using  ferrous  thiocyanate  as  indicator  (Ling  and  Rendle,  Analyst,  1905, 
30,  182)  is  much  quicker  and,  according  to  Ling  and  Jones  (Analyst, 
1908,  33,  160),  quite  as  accurate. 

Note. — In  order  that  results  by  the  gravimetric  method  may  be  calculated  by 
aid  of  the  published  tables,  it  is  necessary  that  the  amount  of  copper  or  oxide  to  be 
weighed  shall  fall  within  certain  limits.  If  the  sugar  content  does  not  exceed  i  grm. 
per  loo  c.c.  the  above  quantities  will  give  a  convenient  precipitate.  If  the  propor- 
tion of  sugar  is  greater  than  i  %  a  smaller  quantity  of  wine  should  be  taken  in 
the  first  instance.  The  sugar  content  is  as  a  rule  not  very  far  from  x  —  2,  where  x 
represents  the  grm.  of  extract  per  100  c.c.  If  therefore  a  wine  shows  4  % 
extract,  it  will  probably  contain  about  2  %  of  sugar,  and  TOO  c.c.  is  then  diluted 
with  an  equal  bulk  of  water,  evaporated  down  to  about  50  c.c.,  cooled  and  made 
up  to  200  c.c.  with  lead  acetate,  etc.,  as  already  described. 

Cane  Sugar. — 50  c.c.  of  the  clarified  solution  taken  for  the  esti- 
mation of  reducing  sugars  are  exactly  neutralised  with  hydrochloric 
acid,  5  c.c.  of  i  %  hydrochloric  acid  added,  and  the  whole  heated 
for  half  an  hour  on  the  water-bath.  The  liquid  is  exactly  neutralised, 
evaporated  somewhat,  made  slightly  alkaline  with  sodium  carbonate 
and  filtered  into  a  50  c.c.  flask,  the  filter  being  washed  until  the  flask 
is  full  to  the  mark.  The  reducing  power  of  this  filtrate  is  now  deter- 
mined by  means  of  Fehling's  solution,  and  the  result  calculated  as  in- 
vert sugar.  As  95  parts  of  cane  sugar  yield  100  parts  of  invert  sugar 
on  hydrolysis,  the  amount  of  cane  sugar  in  100  c.c.  of  the  wine  is  given 
by  x=  0.95  (b-a),  where  a  is  the  amount  of  reducing  sugar,  expressed 
as  invert,  in  100  c.c.  of  the  original  wine,  and  b  the  amount  found  after 
inversion. 

Polarisation. — The  polarimeter  may  give  useful  information  con- 
cerning a  sample  of  wine,  especially  one  suspected  of  sophistication. 
The  following  scheme  may  be  found  useful.  It  remains  nearly  in  the 
words  of  a  Bulletin  of  the  A.  O.  A.  C.,  from  which  it  was  copied  into 
the  last  edition  of  this  work.  As  there  was  one  serious  mistake  the 
present  writer  has  compared  the  whole  scheme  with  the  German  de- 
cree (Veroffent.  d.  kaiserl.  Gesundheitsamtes,  1896,  20,  557)  on  which  it 
was  based  and  has  made  some  minor  alterations  in  the  direction  of  the 
German  model. 

All  results  are  to  be  stated  as  the  polarisation  of  the  undiluted  wine 
in  a  200  mm.  tube.  The  Schmidt  and  Haensch  half-shadow  saccha- 
rimeter  is  to  be  used,  and  the  results  expressed  in  terms  of  the  sugar 


172  WINES    AND    POTABLE    SPIRITS. 

scale  of  this  instrument.  If  any  other  instrument  be  used,  or  if  it  be 
desirable  to  convert  to  angular  rotation,  the  factors  given  on  page  53 
are  to  be  used. 

White  Wines. — 60  c.c.  of  wine  are  neutralised,  evaporated  to  one- 
third,  made  up  again  to  60  c.c.,  treated  with  3  c.c.  of  basic  lead  acetate 
solution  arid  filtered.  31.5  c.c.  of  the  filtrate  are  treated  with  a  i.5.c.c. 
of  a  saturated  solution  of  sodium  carbonate,  filtered,  and  polarised. 
This  gives  a  dilution  of  10  to  n,  which  must  be  considered  in  the  cal- 
culation, and  the  polarimeter  reading  must  accordingly  be  increased 
one- tenth. 

Red  Wines. —  60  c.c.  of  wine  are  neutralised,  evaporated  to  one- 
third,  made  up  again  to  60  c.c.,  decolourised  with  6  c.c.  of  basic  lead 
acetate  solution  and  filtered.  To  33  c.c.  of  the  filtrate  3  c.c.  of  a 
saturated  solution  of  sodium  carbonate  are  added,  the  mixture  filtered, 
and  the  filtrate  polarised.  The  dilution  in  this  case  is  5  to  6,  and  the 
polarimeter  reading  must  accordingly  be  increased  one-fifth. 

Sweet  Wines,  Before  Inversion. — 100  c.c.  are  neutralised,  evapo- 
rated to  one-third,  made  up  again  to  100  c.c.,  decolourised  with  2  c.c. 
of  basic  lead  acetate  solution  and  filtered  after  the  addition  of  8  c.c.  of 
water.  0.5  c.c.  of  the  saturated  solution  of  sodium  carbonate  and 
4.5  c.c.  of  water  are  added  to  55  c.c.  of  the  filtrate,  and  the  liquid 
mixed,  filtered,  and  polarised.  The  polarimeter  reading  is  multiplied 
by  1.2. 

After  Inversion. — 33  c.c.  of  the  filtrate  from  the  lead  acetate  in  (i) 
are  placed  in  a  flask  with  3  c.c.  strong  hydrochloric  acid.  After  mix- 
ing well  the  flask  is  placed  in  water  and  heated  until  a  thermometer, 
placed  in  the  flask  with  the  bulb  as  near  the  centre  of  the  liquid  as 
possible,  marks  68°,  consuming  about  fifteen  minutes  in  the  heating. 
It  is  then  removed,  cooled  quickly  to  room  temperature,  filtered,  and 
polarised,  the  temperature  being  noted.  The  polarimeter  reading  is 
multiplied  by  1.2. 

After  Fermentation. — 50  c.c.  of  wine,  are  dealcoholised  and  made 
up  to  the  original  volume  with  water,  and  mixed  in  a  small  flask  with 
well-washed  beer  yeast  and  kept  at  30°  until  fermentation  has  ceased, 
which  requires  from  two  to  three  days.  The  liquid  is  then  washed 
into  a  100  c.c.  flask,  a  few  drops  of  a  solution  of  acid  mercuric  nitrate 
and  then  basic  lead  acetate  solution,  followed  by  sodium  carbonate, 
added.  The  flask  is  filled  to  the  mark  with  water,  shaken,  and  the 
solution  filtered  and  polarised. 


WINES.  173 

(1)  The  Wine  Shows  No  Rotation. 

This  may  be  due  to  the  absence  of  any  rotatory  body  or  to  the  simul- 
taneous presence  of  dextrorotatory  and  laevorotatory  sugars. 

(a)  The  Wine  is  Inverted. — A  laevorotation  shows  that  the  sample 
contained  cane  sugar. 

(b)  The  Wine  is  Fermented. — A  dextro-rotation  shows   that  both 
laevorotatory  sugar  and  the  unfermentable  constituents  of  commercial 
dextrose  were  present. 

If  no  change  takes  place  in  either  (a)  or  (b)  in  the  rotation  it  proves 
the  absence  of  unfermented  cane  sugar,  the  unfermentable  constituents 
of  commercial  dextrose,  and  of  laevorotatory  sugar. 

(2)  The  Wine  Rotates  to  the  Right'. 

This  may  be  caused  by  unfermented  cane  sugar,  commercial  dex- 
trose, or  both. 

The  Wine  is  Inverted. 

(aj  It  Rotates  to  the  Left  After  Inversion. — Unfermented  cane 
sugar  was  present. 

(a.2)  It  Rotates  More  than  2.3°  to  the  Right.— The  unferment- 
able constituents  of  commercial  dextrose  are  present. 

(a3)  It  Rotates  Less  than  2.3°  and  More  than  0.9°  to  the  Right. 
— It  is  in  this  case  treated  as  follows: 

210  c.c.  of  the  wine  are  evaporated  to  about  one-third  volume  to 
expel  alcohol,  cooled,  diluted  with  water  to  the  original  volume,  and 
fermented  with  2  grm.  of  pressed  yeast.  The  fermented  liquid  is 
evaporated  in  a  porcelain  dish  to  a  thin  syrup  with  a  little  sand  and  a 
few  drops  of  a  20  %  solution  of  potassium  acetate.  To  the  residue  200 
c.c.  of  90  %  alcohol  are  added,  with  constant  stirring.  The  alcoholic 
solution  is  filtered  into  a  flask,  and  the  alcohol  removed  by  distillation 
until  about  5  c.c.  remain.  The  residue  is  mixed  with  washed  bone- 
black,  filtered  into  a  graduated  cylinder,  and  washed  until  the  filtrate 
amounts  to  30  c.c.  If  the  filtrate  shows  a  dextro-rotation  of  more  than 
1.5°  it  indicates  the  presence  of  the  unfermentable  constituents  of  com- 
mercial dextrose. 

(3)   The  Wine  Rotates  to  the  Left. 

It  contains  unfermented  laevorotatory  sugar,  derived  either  from 
the  must  or  from  the  inversion  of  added  cane  sugar.  It  may,  however, 


174  WINES   AND    POTABLE    SPIRITS. 

also  contain  unfermented  cane  sugar  and  the  unfermentable  constitu- 
ents of  commercial  dextrose. 

(a)  The  wine  is  fermented  according  to  the  process  already  de- 

scribed. 
(ax)  It  polarises  3°  after  fermentation.     It  contains  only  laevo- 

rotatory  sugar, 
(a^)  It   rotates   to   the   right.     It   contains  both  laevorotatory 

sugar  and  the  unfermentable  constituents  of  commercial 

dextrose. 

(b)  The  wine  is  inverted  according  to  the  process  already  described. 
(bx)  It  is  more  strongly  laevorotatory  after  inversion.  It  contains 

both  laevorotatory  sugar  and  unfermented  cane  sugar. 

Potassium  Sulphate. — Fifty  c.c.  of  the  original  wine  is  acidified 
with  hydrochloric  acid,  precipitated  hot  with  barium  chloride  and 
the  sulphate  found  calculated  as  potassium  sulphate. 

Sulphurous  Acid. — The  sulphuring  of  casks  is  a  common  and  not 
improper  practice,  but  the  presence  of  a  considerable  amount  of  sul- 
phurous in  wine  indicates  that  sulphites  have  been  added  as  preser- 
vative. Some  of  this  sulphurous  acid  is  combined  with  aldehyde, 
and  since  in  this  form  it  is  said  to  be  less  objectionable  (Marischler, 
Wien.  klin.  Wochenschr.,  1896,  31),  it  is  usual  to  make  two  estima- 
tions, one  of  total  sulphurous  acid,  the  other  of  sulphurous  acid  not 
in  organic  combination,  which  latter  is  in  contradistinction  de- 
scribed as  "free''  sulphurous  acid. 

"Free"  Sulphurous  Acid. — To  50  c.c.  of  the  wine,  contained  in  a 
flask,  a  little  sodium  carbonate  is  added  and  then  excess  of  dilute  sul- 
phuric acid.  The  flask  is  thus  filled  with  carbon  dioxide  and  the 
sulphurous  acid  can  be  titrated  fairly  accurately  with  N/50  iodine 
solution  and  starch. 

Total  Sulphurous  Acid. — 50  c.c.  of  the  wine  are  mixed  in  a  flask 
with  25  c.c.  of  normal  sodium  hydroxide  to  liberate  the  sulphurous 
acid  from  its  combination  with  aldehyde.  After  the  mixture  has 
stood  15  minutes  with  occasional  shaking,  10  c.c.  of  dilute  (1:3)  sul- 
phuric acid  are  added,  and  the  total  sulphurous  acid  quickly  titrated 
with  N/50  iodine  solution. 

More  exact  but  more  complicated  methods  for  the  estimation  of 
total  sulphurous  acid  may  be  found  in  Windisch  (page  133),  Bigelow 
(page  57)  and  in  /.  Soc.  Chem.  Ind.,  1898,  17,  279.  If  the  amount 
of  sulphur  dioxide  permissible  is  fixed  by  law  the  use  of  an  exact 


WINES.  175 

method  is  important.  There  is  a  tendency  for  the  amount  to  be 
slightly  overestimated  by  the  method  just  described,  but  it  is  suffi- 
ciently accurate  for  most  purposes. 

Tannin. — The  following  approximate  method,  due  to  Nessler  and 
Earth  (Zeit.  anal.  Chem.,  1883,  22,  595)  has  many  followers  on  the 
continent.  12  c.c.  of  wine  are  shaken  with  30  c.c.  of  96%  alcohol 
and  filtered.  35  c.c.  of  the  filtrate,  corresponding  to  10  c.c.  of  wine, 
are  evaporated  to  6  c.c.  and  transferred  to  a  measuring  tube  of  pre- 
scribed dimensions,  the  volume  brought  up  to  10  c.c.  by  addition  of 
water,  i  c.c.  .of  40%  sodium  acetate  added  and  finally  i  or  2  drops 
of  10%  ferric  chloride.  The  whole  is  t  hen  shaken  and  after  24 
hours  the  volume  of  the  precipitate  is  read  off.  This  volume  in  c.c. 
multiplied  by  0.033  *s  sa^  to  giye  tne  approximate  percentage  of 
tannin  in  the  wine.  The  lower  part  of  the  measuring  tube  is  0.8  cm. 
wide  and  shows  tenths  of  a  c.c.,  and  is  long  enough  to  hold  about  4 
c.c.;  the  upper  part  is  1.8  cm.  wide  and  has  marks  at  10,  n,  20  and 
22  c.c.  With  red  wines,  it  is  usual  to  add  n  c.c.  of  water  immediately 
after  the  addition  of  the  ferric  chloride  and  before  shaking. 

For  more  exact  work,  Neubauer's  modification  of  Lowenthal's 
method  (see  Tannins,  Vol.  Ill)  is  most  often  employed.  10  c.c.  of 
wine  is  a  convenient  quantity  to  take  for  the  process. 

Salicylic  Acid. — This  properly  belongs  to  another  section  of  this 
work.  Since,  however,  genuine  unsophisticated  wine  may  give  the 
reactions  of  salicylic  acid,  if  large  enough  quantities  are  taken  for  the 
test,  the  German  official  directions  for  carrying  out  the  test  are  given 
here.  It  is  said  that  few  or  no  genuine  wines  will  give  the  characteristic 
reactions  of  salicylic  acid  when  the  test  is  conducted  with  these  quanti- 
ties, whereas  added  salicylic  acid  will  be  infallibly  detected,  since  a 
quantity  undetectable  in  this  way  would  not  appreciably  increase 
the  keeping  properties  of  wine. 

50  c.c.  of  wine  are  shaken  (not  too  vigorously,  lest  an  emulsion 
forms)  with  50  c.c.  of  a  mixture  in  equal  proportions  of  ether  and  petrol- 
leum  spirit.  The  ethereal  layer  is  separated,  filtered  and  evaporated, 
and  the  residue  tested  with  very  dilute  ferric  chloride  solution. 
The  tannin  is  almost  insoluble  in  the  mixture  of  ether  and  petroleum, 
but  if  a  black  or  dark  brown  colour  result  on  the  addition  of  ferric 
chloride,  a  drop  of  hydrochloric  acid  is  added  and  the  extraction  with 
the  solvent  repeated. 

Saccaharin. — In  the  absence  of  salicylic  acid,  any  of  the  methods 


176  WINES   AND    POTABLE    SPIRITS. 

described  under  Saccharin  in  a  later  volume  of  this  work  may  be 
applied.  Methods  depending  on  the  conversion  of  saccharin  into 
salicylic  acid  are  clearly  not  applicable  when  salicylic  acid  is 
present. 

The  following  method,  due  originally  to  Herzfeld  and  Reischauer 
(Deutsche  Zuckerind.,  1886,  124),  was  especially  recommended  by  Allen 
(Analyst,  1888,  13,  105): 

100  c.c.  of  wine  are  mixed  with  coarse  sand  and  evaporated 
on  the  water-bath.  The  residue  is  treated  with  i  or  2  c.c.  of  30  % 
phosphoric  acid  and  repeatedly  extracted  with  a  moderately 
warm  mixture,  in  equal  proportions,  of  ether  and  petroleum  light. 
The  successive  extracts,  which  should  amount  in  all  to  200  c.c.  or  more 
are  filtered  through  asbestos  and  the  greater  part  of  the  solvent  removed 
by  distillation.  The  concentrated  extract  is  poured  into  a  basin,  the 
remainder  of  the  solvent  evaporated,  and  the  residue  taken  up  with 
dilute  sodium  carbonate  solution,  filtered  into  a  platinum  dish  and 
evaporated  to  dryness. 

The  residue  is  mixed  with  4  or  5  times  its  bulk  of  dry  sodium  car- 
bonate and  added  in  small  portions  to  fused  nitre.  The  melt  is 
dissolved  in  water,  acidified  with  hydrochloric  acid  and  precipitated 
with  barium  chloride.  Each  grm.  of  barium  sulphate  corresponds 
to  0.786  grm.  saccharin. 

Boric  Acid. — Methods  of  estimating  this  need  no  description  here, 
but  it  may  be  pointed  out  that  merely  qualitative  tests  are  valueless, 
since  it  is  now  known  that  boric  acid  is  a  normal  constituent  of  wines. 

Fluorides. — For  the  estimation  of  fluorides  in  wine,  Tread  well  and 
Koch  (Zeit.  anal.  Chem.,  1904,  43,  469)  recommend  the  following 
modification  of  Rose's  method.  100  c.c.  of  the  wine  are  rendered 
feebly  alkaline  with  sodium  hydroxide,  and  silver  nitrate  is  added  as 
long  as  it  produces  a  precipitate.  The  mixture  is  then  made  up  to 
250  c.c.,  filtered,  and  200  c.c.  of  the  filtrate  treated  with  an  excess  of 
sodium  chloride,  and  made  up  to  250  c.c.  After  24  hours,  175  c.c.  of 
the  clear  liquid  are  decanted  off  and  treated  with  3  or  4  c.c.  of  2N 
sodium  carbonate,  and  then  boiled  for  five  minutes  with  a  large 
excess  of  calcium  chloride.  The  precipitate  is  collected  on  a  filter, 
washed  with  hot  water,  dried  and  heated  to  dull  redness  for  15  minutes. 
When  cool,  3  c.c.  of  9%  acetic  acid  are  added  to  the  contents  of  the 
crucible  and  the  whole  digested  on  the  water-bath  for  half  an  hour, 
after  which  the  mixture  is  evaporated  to  dryness.  Two  drops  of  9  % 


WINES.  177 

acetic  acid  are  added,  and  the  residue  in  the  crucible  repeatedly 
extracted  with  small  portions  of  hot  water,  which  are  then  passed 
through  a  small  filter.  This  is  subsequently  washed,  dried,  ashed  and 
returned  to  the  crucible  and  the  latter  ignited  and  weighed.  Extraction 
with  acetic  acid  should  be  repeated  until  two  weighings,  differing  by 
less  than  0.5  mg.  are  obtained.  1.6  mg.  are  added  to  the  weight  for 
each  100  c.c.  of  wash-water  used. 

Occasionally,  but  rarely,  chlorine,  lime,  magnesia,  and  potash  are 
estimated  in  wines.  The  methods  for  their  estimation  need  no  de- 
scription here. 

For  the  estimation  of  total  tartaric  acid,  free  tartaric  acid,  potassium 
hydrogen  tartrate,  and  calcium  tartrate,  Halenke  and  Moslinger  (Zeit. 
anal.  Chem.,  1895,  34,  279)  have  worked  out  an  exact  scheme  of 
analysis,  which  is  described  very  fully  by  Windisch  (loc.  cit.,  120). 
These  determinations  are  apparently  considered  of  importance  by 
German  officials,  since  the  methods  of  Halenke  and  Moslinger  are 
set  out  in  some  detail  in  the  Imperial  decree  to  which  reference  has 
already  been  made.  The  results  will  have  more  significance  when  a 
larger  number  of  genuine  wines  have  been  examined  by  the  accurate 
methods  to  which  reference  has  been  made.  Most  of  the  published 
statistics  are  based  on  older  and  less  exact  methods  of  analysis. 

Foreign  Colouring  Matters. — Wines  should  always  be  examined 
for  the  presence  of  coal-tar  colours,  and  tested  as  to  their  behaviour 
with  lead  acetate.  Even  white  wines  may  have  received  an  addition 
of  caramel  or  of  a  coal-tar  colour  specially  prepared  as  a  caramel 
substitute.  Some  cleaned  wool,  mordanted  with  alum  and  sodium 
acetate,  should  be  boiled  with  the  wine  and  any  precipitated  colour 
examined  by  the  usual  reagents  (see  Vol.  V,  and  Green,  /.  Soc. 
Dyers  and  Col.,  1905,  21,  236).  It  is  usually  sufficient  to  establish 
the  presence  of  such  colours,  however,  and  not  necessary  to  identify 
them. 

The  following  tests  have  been  specially  recommended  for  the  detec- 
tion of  foreign  colouring  matters  in  wine. 

Lead  Acetate  Test. — 5  c.c.  of  basic  lead  acetate  solution  are 
added  to  20  c.c.  of  wine.  If  the  resulting  precipitate  is  red-violet  in 
colour,  the  fact  is  strong  evidence  of  the  presence  of  the  colouring  matter 
of  poke  berries  (Phytolacca  decandra).  Bilberry  juice  gives  a  blue 
precipitate  and  mallow  and  elderberry  juice  a  green  one,  but  these 
colours  are  much  less  characteristic  than  that  given  by  poke.  Gen- 
VOL.  I— 12 


178  WINES    AND    POTABLE    SPIRITS. 

uine  wines  may  give  a  grey,  blue-grey,  blue-green  or  green  precipitate, 
but  never  a  red-violet  one.  Another  volume  of  5  c.c.  of  lead  acetate  is 
added  and  the  liquid  warmed  and  filtered.  If  the  filtrate  is  red, 
rosaniline  may  be  suspected,  but  some  genuine  dark  red  wines  are 
only  with  difficulty  decolourised  by  basic  lead  acetate.  If  amyl 
alcohol,  shaken  with  the  filtrate,  assumes  a  red  colour  the  presence  of 
artificial  colouring  matters  may  be  inferred  with  certainty. 

Wool  Test. — White  wool,  mordanted  with  alum  and  sodium  acet- 
ate, is  boiled  with  the  wine  to  which  10%  of  its  bulk  of  10% 
potassium  sulphate  has  been  added.  Genuine  wines  may  impart 
a  red  colour  to  the  wool  which  remains  after  washing,  but  this  colour 
is  much  less  intense  than  that  given  by  minute  traces  of  coal-tar  dyes 
and  may  be  distinguished  by  its  turning  a  dirty  greenish-white  on  treat- 
ment with  ammonium  hydroxide.  If  the  colour  is  of  coal-tar  origin, 
it  will  remain  unchanged  or  change  to  a  yellowish  tint,  which  reverts 
to  red  on  washing  out  the  ammonia. 

Cazeneuve's  Mercuric  Oxide  Test. — 10  c.c.  of  wine  are  shaken 
with  0.2  gr.  yellow  mercuric  oxide  for  at  least  a  minute,  and  when  the 
oxide  has  completely  settled  the  liquid  is  filtered.  Several  thicknesses 
of  paper  are  sometimes  necessary  and  if  a  clear  filtrate  cannot  be 
obtained  in  this  way,  the  experiment  should  be  repeated  and  the 
mixture  heated  to  boiling  before  shaking.  A  clear  but  coloured 
filtrate  indicates  the  presence  of  coal-tar  colours,  but  a  colourless  one 
is  no  proof  of  their  absence,  since  many,  including  the  rosanilines,  are 
absorbed  by  mercuric  oxide.  The  test  serves,  however,  to  detect  acid 
fuchsin,  Bordeaux  red,  and  other  colours  which  escape  the  test  with 
basic  lead  acetate. 

Shaking  with  Ether  Before  and  After  Supersaturation  with 
Ammonium  Hydroxide. — To  100  c.c.  of  wine,  5  c.c.  of  ammonium 
hydroxide  are  added,  and  the  mixture  shaken  with  30  c.c.  of  ether. 
Another  100  c.c.  of  wine  are  shaken  with  ether  without  the  addition  of 
ammonia.  From  each  ethereal  layer,  20  c.c.  are  withdrawn  with  a 
pipette  and  allowed  to  evaporate  in  a  basin  containing  a  thread  of 
wool  about  2  inches  long.  If  the  wool  from  the  experiment  in  which 
the  ammonia  was  used  is  dyed  red,  the  presence  of  coal-tar  colours 
may  be  inferred.  With  genuine  wines  the  wool  from  the  experiment 
in  which  ammonia  was  used  remains  perfectly  white,  while  that  from 
the  experiment  without  ammonia  usually  acquires  a  brownish  tint. 
The  test  serves  for  the  detection  of  rosanilin,  safranin  and  chrysoidin, 


WINES.  179 

but  acid  fuchsin  and  many  other  colours  which  may  be  present  are 
not  detected  by  it. 

Shaking  with  Amyl  Alcohol. — This  test  is  best  performed  in  tripli- 
cate: (a)  on  the  original  wine;  (b)  on  the  wine  made  acid  with  sul- 
phuric acid,  and  (c)  on  the  wine  made  alkaline  with  ammonia.  One 
hundred  c.c.  of  wine  and  30  c.c.  of  amyl  alcohol  are  convenient 
quantities. 

a.  If  the  amyl  alcohol  is  coloured  red  the  presence  of  artificial  colour- 
ing matter  is  not  necessarily  to  be  inferred,  since  many  high-coloured 
young  wines  yield  red  colouring  matter  to  amyl  alcohol.     If  on  the 
addition  of  a  few  drops  of  ammonia  the  colour  remains  unchanged, 
the    presence    of   coal-tar    colours    is    tolerably    certain,    since    the 
red  colour  of  genuine  wines  is  changed  to  blue  or  green  on  such 
treatment. 

b.  The  amyl  alcohol  extract  from  acidified  red  wines  is  generally 
red,  but  any  artificial  colour  is  concentrated  by  the  treatment  and 
separated  from  some  other  matters  which  may  mask  its  reactions.    The 
amyl  alcohol  is  shaken  with  water  and  the  aqueous  solution  tested  with 
ammonia  or  submitted  to  the  wool  test. 

c.  If  the  amyl  alcohol  extract  from  the  ammoniacal  wine  is  red,  the 
presence  of  coal-tar  colours  may  be  safely  inferred.     If  it  is  colour- 
less the  experiment  should  be  repeated,  using  less  ammonia  since  in 
presence  of  a  large  excess  (above  3  %)  of  ammonia  the  amyl  alcohol  may 
remain  colourless  even  when  coal-tar  colours  are  present. 

The  detection  of  caramel  in  wine  is  less  important  now  than  it  was 
some  years  ago,  since  tar  colours  have  been  specially  prepared  to  replace 
it,  and  the  necessary  quantity  of  these  tar  colours  is  so  small  that  their 
expense  is  negligible,  and  the  sophisticator  probably  thinks  them  less 
easy  of  detection.  In  point  of  fact,  the  time-honoured  tests  for  cara- 
mel fail  to  detect  modern  preparations  sold  under  this  name.  This 
is  not  surprising  since  the  caramel  of  to-day  is  a  widely  different  product 
from  the  burnt  sugar  of  twenty  years  ago ;  it  contains  a  notable  propor- 
tion of  amino -compounds  and  is  chemically  very  different  from  earlier 
preparations,  in  the  published  analyses  of  which  nitrogen  was  never 
recorded.  The  white-of-egg  test  of  Carles  (/.  Pharm.  Chim.,  1875, 
22,  177)  remains  in  all  the  text-books,  although  a  liquid  coloured  by 
a  modern  preparation  of  caramel  loses  quite  as  much  colour  as  many 
genuine  wines  on  treatment  with  white  of  egg.  Schidrowitz  (/.  Soc. 
Chem.  Ind.,  1902,  21,816)  has  doubly  discredited  Amthor's  paralde- 


l8o  WINES   AND    POTABLE    SPIRITS. 

hyde  test  (Zeit.  anal.  Chem.,  1885,  24,  30)  which  may  discover  caramel 
where  there  is  none  and  fail  to  discover  it  when  actually  present. 

In  the  writer's  experience,  however,  caramel  will  be  readily  enough 
detected  by  the  general  tests  already  given.  Contrary  to  the  statements 
in  the  text-books,  caramel,  of  English  manufacture  at  least,  is  not  decol- 
ourised by  basic  lead  sub-acetate  so  that  this  test  will  show  the  presence 
of  foreign  colouring  matter  of  some  sort.  The  comparative  insolubility 
of  the  colour  in  amyl  alcohol  and  its  almost  complete  insolubility  in 
ether  will  serve  to  distinguish  it  from  coal-tar  colours  if  it  is  necessary 
to  do  this. 

The  foregoing  tests  have  many  years'  successful  application  to  re- 
commend them.  No  single  one  of  them  will  carry  the  analyst  very 
far,  but  if  they  are  all  applied,  few  artificially  coloured  wines  will  escape 
detection.  Those  few  will  be  coloured  with  bilberry  juice  or  similar 
fruit  juice,  and  the  methods  described  for  the  detection  of  bilberry 
juice  are  so  troublesome  and  withal  so  uncertain  that  they  are  scarcely 
worth  description  here. 

New  methods  for  the  detection  of  foreign  colouring  matters,  espe- 
cially of  magenta,  in  wines  are  described  each  year,  and  occasionally 
the  claim  is  made  for  a  new  test  that  it  enables  the  analyst  by  a  single 
operation  to  decide  whether  a  sample  has  been  artificially  coloured  or 
not.  The  continued  use  of  the  older,  more  troublesome  methods  by 
experienced  analysts  must  be  taken  as  evidence  that  the  comprehensive- 
ness of  the  new  tests  yet  lacks  proof. 

One  of  the  best  of  recent  suggestions  is  that  of  Jean  and  Frabot 
(Ann.  chim.  anal.,  1907,  12,  52,  and  Bull.  Soc.  Chim.,  1907,  I,  748). 
Extending  some  experiments  of  Trillat,  these  authors  find  that  all 
genuine  wines  yield  a  colourless  filtrate  when  treated  as  follows:  50 
c.c.  of  the  wine  is  warmed  on  the  water-bath  with  i  c.c.  of  formalin 
and  4  c.c.  of  hydrochloric  acid.  When  a  precipitate  has  formed,  an  ex- 
cess of  ammonia  is  added  and  the  heating  continued  till  all  the  free 
ammonia  has  been  expelled.  The  liquid  is  then  cooled  and  filered. 
They  also  find  that  artificially  coloured  wines  when  treated  in  this 
way  yield  a  coloured  filtrate.  It  is  useful  to  know  that  all  genuine 
wines  which  have  been  tested  in  this  way  yield  colourless  filtrates, 
but  it  would  be  unwise  to  regard  such  a  colourless  filtrate  as  proof  that 
no  colour  other  than  that  natural  to  the  wine  was  present. 

The  following  method,  due  to  Dupre  (/.  Chem.Soc.,  1880,  37,  572), 
has  been  useful  to  many.  The  best  colourless  commercial  gelatin  is  dis- 


WINES.  l8l 

solved  in  ten  parts  of  boiling  water,  and  the  solution  poured  into  a  soup- 
plate  or  other  flat  vessel.  When  cold  and  thoroughly  set,  a  cube  about 
j  in.  on  the  side  is  cut  from  the  jelly  by  means  of  a  sharp  knife  and 
placed  in  the  sample  of  wine  to  be  tested.  After  standing  24  hours, 
the  cube  is  removed,  washed  a  little  with  cold  water,  and  a  central 
slice  cut  out  of  it  in  a  direction  parallel  to  one  of  the  sides.  On  ex- 
amining this  section,  it  will  be  found,  in  the  case  of  a  pure  wine,  that 
the  colouring  matter  has  penetrated  but  a  very  little  way  into  the  jelly 
(perhaps  1/16  in.),  whereas  the  great  majority  of  foreign  colouring 
matters  will  have  penetrated  to  the  very  centre  of  the  cube. 

Of  a  large  number  of  colouring  matters  only  that  of  alkanet-root  re- 
sembles the  "cenolin"  of  pure  wine  in  the  slow  rate  at  which  it  diffuses 
into  the  jelly.  Hence,  if  coloration  of  the  interior  of  the  jelly  is  not 
observed,  alkanet  is  the  only  foreign  colouring  agent  likely  to  be  present. 
It  may  be  distinguished  by  its  absorption-spectrum,  which,  at  a  certain 
concentration  of  the  acidulated  solution,  shows  three  distinct  absorp- 
tion-bands between  the  sodium  line  and  the  blue  strontium  line,  and 
nearly  equidistant  from  these  lines  and  from  each  other.  Ammonia 
changes  the  colouring  matter  of  alkanet  to  blue,  and  reduces  the 
absorption-bands  to  two,  one  coincident  with  the  D  line  and  the 
other  less  refrangible  than  that.  Both  acid  and  alkaline  solutions  pro- 
duce a  general  absorption  of  the  violet  end  of  the  spectrum,  and  in 
moderately  concentrated  solutions  only  the  red  is  transmitted. 

The  colouring  matter  of  pure  red  wine  produces  a  general  absorption 
in  all  parts  of  the  spectrum  except  the  red,  but  generally  no  distinct 
absorption-band.  The  red  colour  is  changed  to  greenish-brown  on 
addition  of  ammonia,  and  the  liquid  then  shows  an  indistinct  absorp- 
tion-band in  the  orange-yellow  region. 

If  the  colouration  of  the  cube  of  jelly  points  to  the  presence  of  a  foreign 
colouring  matter,  the  nature  of  this  may  frequently  be  ascertained,  if 
desired.  As  a  rule,  the  slice  of  jelly  shows  the  colour  proper  to  the  added 
substance  much  more  clearly  than  did  the  wine  itself,  and  a  difference 
between  the  two  colours  is  a  strong  indication  of  the  presence  of  a  foreign 
matter.  Indigo  and  logwood  may  thus  be  readily  discovered.  The 
absorption-spectrum  exhibited  by  the  slice  will  serve  for  the  detection 
of  rosaniline,  cochineal,  beet-root,  red-cabbage,  litmus  etc.,  and  further 
information  may  be  gained  by  placing  the  slice  in  dilute  ammonia. 
Thus  treated,  a  slice  coloured  with  rosaniline  becomes  colourless;  with 
red  cabbage,  dark  green;  with  cochineal,  purple,  and  with  logwood, 


l82  WINES   AND    POTABLE    SPIRITS. 

brown.  This  last  reaction  is,  however,  frequently  produced  in  the 
absence  of  logwood.  When  present,  the  slice  will  be  coloured  brown 
or  yellow  to  a  considerable  depth  before  it  is  treated  with  ammonia. 
Operating  in  the  above  manner,  Dupre  found  that  an  addition  of 
foreign  colouring  matter  equal  to  10  %  of  the  total  intensity  of  the 
colour  of  the  wine  could  usually  be  readily  detected,  and  in  no  case 
could  20  %  be  overlooked.  In  the  case  of  logwood  5  %  could  be 
recognised,  and  as  little  as  i  %  of  rosaniline  could  be  found.  In 
making  the  tests  it  is  desirable  to  compare  the  sample  with  a  pure 
wine  of  the  same  kind. 


SIGNIFICANCE    OF   RESULTS    OF    WINE   ANALYSIS. 

The  chemist  who  needs  to  refer  to  a  general  work  of  this  kind  for  ana- 
lytical methods  will  presumably  only  seek  to  know  how  he  may  dis- 
tinguish genuine  wine  from  sophisticated  beverages.  The  significance 
of  the  results  to  the  owner  or  intending  purchaser  of  wine  of  undoubted 
genuineness  but  doubtful  capacity  for  improvement  on  keeping  can- 
not be  dealt  with  here,  experience  of  the  wines  of  a  particular  district 
and  the  possession  of  a  trained  palate  are  indispensable  to  the 
formation  of  a  sound  judgment  of  the  future  behaviour  of  a  wine. 

The  following  notes  assume  that  the  analyst  is  concerned  only  in 
deciding  as  to  the  genuineness  or  otherwise  of  a  sample.  Thus  the 
alcoholic  content  is  described  as  of  small  significance,  which  from  this 
standpoint  is  true,  but  to  a  wine  expert  a  difference  of  2%  may 
suggest  a  great  deal  as  to  the  relative  stability  of  two  wines. 

The  standards  most  respected  in  France  and  Germany  are  appli- 
cable only  to  wines  which  should  be  the  product  of  fermentation  of  nor- 
mal grape-musts,  without  concentration  of  these  musts  or  addition  of 
alcohol,  sugar  or  other  substance.  They  are  occasionally  subjected  to 
criticism  even  in  the  countries  of  their  origin,  and  it  would  be  unfair  to 
apply  them  to  the  wines  of  other  countries.  The  standards  which 
have  been  proposed  for  certain  sweet  wines  are  of  still  narrower  ap- 
plication, and  there  are  insufficient  data  available  concerning  the  wines 
of  Spain  and  Portugal  to  justify  any  standards  for  the  admittedly  forti- 
fied wines  of  those  countries.  Except  when  otherwise  stated,  the 
following  notes  refer  only  to  wines  which,  if  genuine,  are  the  undiluted 
product  of  the  fermentation  of  pure  grape-musts,  and  the  word 
"genuine"  when  used  is  to  be  understood  in  this  sense. 


WINES.  183 

Specific  Gravity. — This  is  of  small  significance  in  judging  a  wine, 
and  the  main  purpose  of  ascertaining  it  is  the  estimation  of  extract 
by  the  indirect  method.  The  sp.  gr.  of  wines  derived  by  natural 
fermentation  from  the  juice  of  the  grape,  without  concentration  or 
addition  of  any  kind,  is  never  far  from  unity,  seldom  less  than  0.99 
and,  according  to  certain  French  authorities,  never  less  than  0.985.  In 
wines  which  may  properly  be  derived  from  concentrated  musts  or  to 
which  the  addition  of  alcohol  is  a  recognised  practice,  the  variations 
in  sp.  gr.  may  be  very  great. 

Alcohol. — The  alcohol  content  of  genuine  wines  usually  lies  be- 
tween 5  and  10  grm.  per  100  c.c.,  but  numbers  as  low  as  2.1  and  as 
high  as  12.2  have  been  recorded.  Alcohol  in  excess  of  14.5  grm.  per 
100  c.c.  would  be  certain  evidence  of  added  spirit,  but  it  must  be  re- 
membered that  even  in  Germany  such  addition  is  permitted  by  law, 
provided  it  does  not  exceed  0.8  grm.  per  100  c.c.  of  wine.  Since  the 
alcohol  content  of  genuine  wine  may  vary  so  widely,  the  number  is  of 
small  value  in  determining  whether  a  sample  has  been  diluted  with 
water. 

Glycerol. — The  proportion  of  glycerol  usually  lies  between  0.4  and 
i%  but  may  be  as  low  as  0.16  or  as  high  as  1.4. 

Alcohol-glycerol  Ratio. — German  chemists  attach  more  im- 
portance to  this  number  than  to  the  absolute  percentages  of  alcohol  or 
glycerol,  and  this  is  reasonable,  but  the  standards  set  up  some  years 
ago  require  amendment  even  for  German  wines.  It  was  formerly 
supposed  that  the  ratio  of  alcohol  to  glycerol  in  genuine  wines  always 
lay  inside  the  limits  100  :  7  and  100  114.  A  wine  which  showed  a  higher 
ratio  of  alcohol  to  glycerol  than  100  :  7  was  held  to  have  been  fortified 
by  addition  of  spirit,  while  if  the  ratio  fell  below  100 :  14,  addition 
of  glycerol  was  suspected.  It  is  now  known  that  in  genuine 
Rhine  wines  the  alcohol-glycerol  ratio  may  exceed  100 :  6  or  fall 
below  100  :  19.  If  100  :  5  and  100 :  20  be  taken  as  the  limits,  few 
genuine  European  wines  will  be  excluded,  but  Bigelow  has  pointed 
out  that  the  average  alcohol-glycerol  ratio  for  American  wines  is 
about  100:6  and  in  his  table  are  included  wines  in  which  it  is  as 
high  as  100 :  2. 

Extract. — The  percentage  of  sugar  varies  within  wide  limits,  and 
plastered  wines  may  contain  notable  quantities  of  potassium  sulphate. 
Apart  from  these  two  constituents,  the  percentage  of  solids  in  solution 
in  young  wines  is  fairly  constant  and  has  been  ascertained  to  be  never 


184  WINES    AND    POTABLE    SPIRITS. 

less  than  a  certain  amount.  Unfortunately,  French  chemists  are  not 
content  with  recording  the  extract  less  sugar  and  potassium  sulphate, 
but,  since  these  latter  are  normally  present  in  small  amount,  they 
define  " reduced  extract"  as  x—  (S  —  o.  i)  —  (K— o.  i),  where  x,  S  and 
K  represent  the  percentage  of  extract,  sugar  and  potassium  sulphate  in 
the  wine.  For  the  purpose  of  comparison  with  arbitrary  standards  the 
simpler  formula  x  —  S  —  K  would  serve  equally  well,  but  in  this  and 
the  following  paragraphs  the  expression  "reduced  extract"  is  used  in 
the  French  sense.  The  reduced  extract  of  genuine  white  wine  of 
continental  origin  is  seldom  less  than  1.6  grm.  per  1000  c.c.  that  of  red 
wine  seldom  less  than  1.8  grm.  The  amount  of  extract  decreases  with 
age,  but  seldom  falls  below  1.5  grm.  Bigelow  quoting  M.  Curtis, 
of  San  Francisco,  says  that  American  red  wine  is  to  be  viewed  with 
suspicion  if  it  contain  less  than  2.4  or  more  than  3.3  grm.  reduced 
extract  per  1000  c.c.  For  American  white  wine  he  places  the  limits  at 
1.5  and  2.4  grm. 

Alcohol-extract  Ratio. — In  France  more  importance  is  attached 
to  this  number  than  to  the  ratio  of  glycerol  to  alcohol.  It  is  said  that 
for  genuine  red  wines  the  ratio  never  exceeds  4.5,  while  for  white  wines 
it  may  be  higher  but  is  never  in  excess  of  6.5.  Higher  values  are  to 
be  taken  as  proof  of  added  alcohol.  This  test  is  more  severe  when 
the  French  method  of  determining  extract  is  used,  since  by  that  method 
glycerol  is  largely  driven  off,  and  a  lower  number  obtained  for  the 
extract. 

Ash. — The  ash  content  of  wines  usually  lies  between  0.2  and  0.3% 
but  genuine  wines  have  been  known  to  contain  as  little  as  o.n 
and  as  much  as  0.44.  A  smaller  amount  than  0.14%  would 
justify  suspicion,  but  it  is  less  easy  to  fix  an  upper  limit,  though 
it  may  be  fairly  said  that  0.35  is  rarely  exceeded.  The  ash 
follows  the  reduced  extract  to  some  extent,  and  is  higher  for  red 
wines.  In  attempting  to  draw  conclusions  from  the  amount  of  ash 
it  is  well  to  deduct  from  this  the  percentage  of  potassium  sulphate 
found  less  o.i. 

Total  Acid. — The  total  acid,  calculated  as  tartaric  acid,  is  seldom 
less  than  0.4  or  more  than  1.5%.  In  France  the  total  acid  is  calcu- 
lated as  sulphuric  acid,  and  it  is  held  that  the  sum  of  the  alcohol 
(expressed  as  c.c.  per  100  c.c.)  and  the  acid  (calculated  as  grm.  of 
sulphuric  acid  per  1000  c.c.)  is  never  less  than  12.5  for  a  genuine  wine. 
A  lower  value  is  held  to  be  evidence  of  dilution  with  water.  This  is  per- 


WINES.  185 

haps  the  most  frankly  empirical  standard  which  has  been  applied  to 
wines,  but  it  has  behind  it  the  experience  of  a  whole  generation  of 
French  chemists  and  may  presumably  be  applied  with  confidence  to 
wines  purporting  to  be  of  French  origin.  When  the  alcohol-extract 
ratio  exceeds  4.5  for  red  wines  or  6.5  for  white  wines,  the  "natural" 
percentage  of  alcohol  is  substituted  for  that  actually  found.  For 
example,  if  a  red  wine  contains  12  grm.  alcohol  and  1.5  grm.  reduced 
extract  per  100  c.c.,  it  is  obvious  that  alcohol  has  been  added.  This 
added  alcohol  must  not  be  taken  into  account  in  applying  the  test 
for  added  water.  Instead,  the  extract,  1.5,  is  multiplied  by  4.5  to  give 
the  " natural  percentage"  by  weight  of  alcohol,  and  then  divided  by  0.8 
to  obtain  the  percentage  by  volume.  To  the  number  so  obtained,  in 
this  case  8.5,  the  acidity  in  grm.  per  1000  c.c.  is  added,  and  if  the  sum 
is  less  than  12.5  it  may  be  taken  as  evidence  that  both  water  and  alcohol 
have  been  added. 

Volatile  Acid. — The  volatile  acid,  calculated  as  acetic  acid,  is 
usually  below  0.08  %  and  wine  containing  much  more  than  0.15 
would  be  condemned  not  as  fraudulent,  but  as  unsound.  As  has  been 
said  already,  considerable  experience  is  necessary  in  forming  judgments 
of  soundness.  Thus  a  wine  high  in  alcohol  might  be  and  remain  quite 
sound  although  the  volatile  acid  was  as  high  as  0.15  \\hile  another 
poor  in  alcohol  and  otherwise  deficient  might  have  less  than  o.io  per 
cent,  and  be  quite  unmerchantable.  A  trained  palate  is  of  the  first 
importance  here. 

Sugar. — The  sugar  content  of  dry  wines  is  of  the  order  of  0.1%. 
In  the  Paris  municipal  laboratory  it  is  usual  to  add  together  the 
sugar  and  twice  the  alcohol,  both  expressed  as  grm.  per  100  c.c., 
and  if  this  sum  exceeds  32.5,  to  decide  that  the  wine  has  received  an 
addition  of  alcohol  or  sugar. 

Potassium  Sulphate. — The  juice  of  the  grape  contains  sulphates 
equivalent  to  perhaps  0.05  %  of  potassium  sulphate  and  a  further 
amount  results  from  the  sulphuring  of  casks,  so  that  wines  on  the  aver- 
age contain  about  o.i  %.  An  amount  in  excess  of  0.2  %  is  held  to 
be  evidence  of  plastering — that  is,  of  the  addition  of  gypsum  to  the 
must — a  practice  which  is  most  common  in  the  sherry  district, 
though  not  confined  to  it.  It  is  impossible  to  discuss  here  the  complex 
reasons  for  the  practice  or  the  arguments  which  have  been  brought 
against  it  by  hygienists.  Red  wines,  except  sweet  dessert  wines, 
must  not  in  Germany  contain  more  than  0.2%  of  potassium  sul- 


1 86  WINES   AND    POTABLE    SPIRITS. 

phate,  and  similar  regulations  apply  to  the  sale  of  wines  in  France  and 
Switzerland. 

Sulphurous  Acid.— In  France  and  Switzerland,  sulphurous  acid 
in  excess  of  200  mg.  per  1000  c.c.  is  forbidden,  whilst  the  "free" 
sulphurous  acid  must  not  exceed  30  mg.  per  1000  c.c.  in  France  or  20 
mg.  per  1000  c.c.  in  Switzerland. 

Most  of  the  work  in  connection  with  wine  has  been  carried  out  in 
Germany  and  France,  and  the  standards  suggested  by  French  and 
German  chemists  are  strictly  applicable  only  to  the  wines  typical  of 
those  countries,  the  red  and  white  Bordeaux  wines,  and  hocks.  All 
these  are  or  should  be  natural  wines.  The  same  standards  may  with 
a  considerable  amount  of  caution  be  applied  to  the  wine  of  any  other 
country  if  that  wine  purports  to  be  a  natural  wine.  But  wines  are  sel- 
dom so  labelled;  they  have  a  distinctive  name.  The  word  " claret" 
has  a  perfectly  definite  significance  in  England.  The  purchaser  expects 
a  wine  grown  in  the  Bordeaux  district,  treated  in  the  manner  usual  in 
that  district  and  having  the  character  common  to  wines  of  that  name. 
The  analyst  would  not  pass  as  genuine  claret  a  sample  which  showed 
signs  of  being  fortified  or  heavily  plastered.  Suppose,  however,  the 
sample  is  sold  as  "  Spanish  claret, "  and  proves  to  be  fortified  and  heavily 
plastered.  The  typical  wine  largely  exported  from  Spain  is  sherry, 
which  is  always  fortified  and  always  plastered,  and  it  might  be  argued 
with  some  truth  that  fortifying  and  plastering,  though  they  found  their 
highest  development  in  the  manufacture  of  sherry,  were  not  restricted 
to  sweet  wines  but  were  more  or  less  typical  of  Spanish  practice.  Cer- 
tainly wines  of  every  degree  of  sweetness  and  alcoholic  strength  from  a 
typical  claret  up  to  something  indistinguishable  from  sweet  port  are 
sold  in  Spain  itself  under  one  name.  Such  a  note  of  warning  is  neces- 
sary, as  wines  of  every  type  are  now  being  produced  in  four  continents, 
and  it  is  doubtful  if  the  purchaser  of  Australian  burgundy  or  Califor- 
nian  sauterne  has  any  right  to  expect  more  than  a  reasonable  resem- 
blance to  previous  consigments  bearing  the  same  label. 

Port,  sherry  and  other  Spanish  wines  less  frequently  imported  to 
this  country,  marsala  and  many  Italian  wines,  and  madeira  always 
receive  an  addition  of  alcohol  to  arrest  fermentation,  and  cane  sugar 
is  a  normal  addition  to  sparkling  wines.  No  champagne  maker 
would  risk  his  valuable  crop  by  using  anything  but  refined  cane  sugar, 
but  in  Germany  it  has  been  found  necessary  to  institute  penalties  to 
prevent  the  use  of  commercial  glucose. 


POTABLE    SPIRITS.  187 

CIDER. 

The  literature  of  cider  continues  to  grow,  French  and  American 
chemists  being  responsible  for  most  of  the  work,  but  no  special  analyt- 
ical methods  of  importance  have  been  described.  Most  of  the  methods 
applied  to  wines  may  be  extended  to  cider.  It  is  usual  to  calculate  the 
non-volatile  acid  as  malic  acid  and  to  return  it  as  such.  The  state- 
ment which  appears  in  the  text-books,  for  example  in  the  last  edition 
of  this  work,  that  the  solid  matter  of  cider  differs  from  that  of  wine  in 
the  presence  of  malic  acid,  seems  to  rest  on  this  convention  rather  than 
on  the  results  of  analyses  directed  to  the  differentiation  of  malic  and 
tartaric  acids.  A  method  for  the  differentiation  of  malic,  tartaric  and 
succinic  acids  in  wines,  etc.,  has  been  worked  out  by  Schmit  and 
Hiepe  (Zeit.  anal.  Chem.,  1882,  21,  534)  and  may  be  found  described  in 
Windisch  (loc.  cit.,  185).  The  method  is  said  to  be  accurate,  but  it  is 
very  tedious  and  of  doubtful  utility.  So  far  as  it  has  been  applied  to 
wines,  the  results  seem  to  indicate  that  malic  acid  may  be  the  chief 
constituent  of  the  non-volatile  acid  of  grape  wines  as  well  as  of  cider. 

In  the  Paris  municipal  laboratory  it  is  held  that  dry  cider — that 
is,  cider  containing  less  than  i%  sugar — should  not  contain  less 
than  3%  of  alcohol  by  volume.  In  judging  sweet  cider,  the  sugar 
percentage  less  i  is  divided  by  2  and  then  by  0.79  and  the  num- 
ber so  obtained  added  to  the  actual  alcohol  percentage.  The  same 
authority  fixes  the  minimum  extract  percentage  of  genuine  cider  at  1.8, 
and  the  minimum  ash  at  0.17%.  This  latter  figure  should  be 
0.15  or  less  for  English  cider,  whilst  a  higher  alcohol  percentage,  say  4, 
might  not  unreasonably  be  insisted  on.  Information  on  the  manufac- 
ture of  English  cider  may  be  found  in  a  pamphlet  by  F.  J.  Lloyd,  pub- 
lished by  the  Board  of  Agriculture  in  1903. 

POTABLE  SPIRITS. 

The  estimation  of  alcohol  in  potable  spirits  does  not  call  for 
special  consideration  here.  It  is  usually  estimated  from  the  sp/gr.  of 
the  distillate  on  the  assumption,  not  quite  correct,  that  the  distillate 
consists  solely  of  water  and  alcohol.  The  error  introduced  by  this 
assumption  is,  with  most  spirits,  very  small. 

Higher  Alcohols. — The  only  method  which  can  be  recommended 
is  the  Allen-Marquardt  method.  Two  others  must,  however,  be  de- 


l88  WINES   AND    POTABLE    SPIRITS. 

scribed  in  some  detail,  partly  because  they  have  official  sanction  in  cer- 
tain foreign  countries,  but  more  particularly  because  the  analyst  may  be 
asked  by  his  clients  to  apply  these  specific  tests  in  order  that  the  re- 
sults may  be  compared  with  older  records  or  with  the  numbers  re- 
turned by  a  continental  chemist  to  whom  the  same  sample  has  been 
submitted. 

Allen-Marquardt  Method. — The  following  description  differs 
slightly  from  that  given  by  Allen  in  the  last  edition  of  this  work,  in  that 
certain  suggestions  of  Schidrowitz  (J.Soc.  Chem.  Ind.,  1902,  21,  815) 
have  been  adopted.  To  200  c.c.  of  the  sample  about  i  c.c.  of  strong 
potash  solution  is  added  and  the  whole  boiled  for  an  hour  under  a 
reflux  condenser.  The  liquid  is  then  transferred  to  a  distilling  flask 
through  the  cork  of  which  there  passes,  to  within  a  few  mm.  of  the 
bottom  of  the  flask,  a  tube  for  the  introduction  of  steam.  Before 
•connecting  up  with  the  supply  of  steam,  distillation  is  commenced  by 
•the  use  of  an  ordinary  gas-burner  and  continued  till  only  about  20  c.c. 
is  left.  Steam  is  then  turned  on  and  the  flame  under  the  flask  so  regu- 
lated that  the  contents  of  the  same  are  reduced  to  about  10  c.c.  by  the 
time  300  c.c.  in  all  have  passed  over.  The  distillate  is  divided  into 
two  equal  parts  and  each  is  treated  in  the  following  manner,  thus  giving 
a  duplicate  determination  of  the  higher  alcohols: 

A  saturated  solution  of  common  salt  is  added  to  the  liquid  until  the 
resulting  mixture  has  a  sp.  gr.  of  at  least  i.i,  when  it  is  extracted 
in  a  separator  four  times  with  carbon  tetrachloride,  using  40  c.c. 
of  the  tetrachloride  for  the  first  extraction,  30  c.c.  for  the  second,  20  c.c. 
for  the  third,  and  10  c.c.  for  the  last  extraction.  The  carbon  tetra- 
chloride now  contains  all  the  higher  alcohols,  and  some  ethyl  alcohol. 
To  remove  the  latter,  the  carbon  tetrachloride  is  shaken  with  50  c.c.  of 
brine,  and  after  this  has  been  separated  it  is  shaken  with  50  c.c.  of  a 
.saturated  solution  of  sodium  sulphate  to  remove  the  chloride.  The 
carbon  tetrachloride  is  next  treated  with  an  oxidising  mixture  consisting 
of  5  grm.  of  potassium  dichromate,  2  grm.  of  strong  sulphuric  acid, 
and  10  c.c.  of  water.  The  oxidation  is  carried  out  in  a  flask  which  is 
connected  to  a  reflux  condenser,  the  liquid  being  kept  gently  boiling 
by  means  of  a  water-bath  for  at  least  eight  hours.  Any  higher  alcohols 
extracted  by  the  carbon  tetrachloride  will  by  this  treatment  be  con- 
verted into  their  corresponding  acids.  After  oxidation,  the  liquid  is 
diluted  with  30  c.c.  of  water,  and  distilled  over  a  naked  flame  until  only 
.20  c.c.  remain  in  the  flask,  which  is  provided  with  a  tube  for  the  in- 


POTABLE    SPIRITS.  189- 

troduction  of  steam  as  in  the  first  distillation.  Steam  is  now  turned 
on,  and  the  flame  under  the  flask  so  regulated  that  not  much  more 
than  5  c.c.  remains  when  the  total  distillate  measures  300  c.c.  Dis- 
tillation is  then  stopped  and  the  distillate  titrated  with  N/io  barium 
hydroxide,  using  methyl-orange  as  the  indicator,  and  shaking  the 
liquid  thoroughly  after  each  addition.  The  amount  of  alkali  required 
to  neutralise  the  liquid  at  this  stage  should  not  exceed  2  c.c.,  and 
generally  less  is  required.  Phenolphthalein  is  next  added  to  the 
liquid,  and  the  titration  continued  until  the  neutral  point  is  reached 
with  this  last  indicator.  Each  c.c.  of  N/ 10  alkali  required  in  the  second 
stage  of  the  titration  corresponds  to  0.0088  grm.  of  higher  alcohols 
expressed  as  amyl  alcohol.  The  alkali  added  when  titrating  with 
methyl-orange  was  formerly  supposed  to  represent  mineral  acid  which 
distilled,  and  is  still  usually  not  taken  into  account. 

Notes  on  Above  Method. — The  brine  is  best  made  by  saturating 
water  with  clean  table  salt,  adding  dilute  sulphuric  acid  until  the  liquid 
has  a  distinctly  acid  reaction,  and  filtering  the  solution. 

The  carbon  tetrachloride  intended  for  use  in  the  process  must  be 
previously  purified  by  treatment  with  chromic  acid  mixture  and  sub- 
sequent distillation  over  barium  carbonate.  The  carbon  tetrachloride 
recovered  at  the  end  of  the  process  may  after  similar  treatment  be  used 
again. 

The  corks  used  in  distilling  the  spirit  must  be  kept  separate  from 
those  used  during  and  after  the  oxidation  process.  They  are  liable  to 
absorb  amyl  alcohol  and  valeric  acid,  to  prevent  which  they  must  all 
be  carefully  covered  with  tinfoil.  Rubber  bungs  should  not  be  used. 
Schidrowitz  and  Kaye  (Analyst,  1905,  30,  191)  recommend  a  con- 
denser tube  ground  to  fit  the  neck  of  the  flask  used  during  the  eight 
hours'  digestion.  They  also  recommend  the  use  of  a  Young's  "rod-and- 
disc"  apparatus  (Trans.  Chem.  Soc.,  1899,  75,  689)  inside  the  24  in. 
condenser-tube. 

The  steam  used  for  the  final  distillation  must  be  free  from  carbon 
dioxide,  since  phenolphthalein  is  to  be  used  as  indicator.  This  con- 
dition is  easily  satisfied  by  having  the  steam  can  or  flask  briskly  boiling 
some  minutes  before  steam  is  wanted. 

The  methyl-orange  acidity  was  formerly  attributed  to  hydrochloric 
acid,  and  consequently  not  taken  into  account  in  calculating  the  higher 
alcohols,  of  which  the  total  acidity  less  the  methyl-orange  acidity  was 
held  to  be  the  measure.  It  has  been  pointed  out  by  Schidrowitz  and 


WINES   AND    POTABLE    SPIRITS. 

Kaye  (Analyst,  1906,  31,  183)  that  in  the  neutralised  liquid  resulting 
from  the  final  titration  of  a  carefully  conducted  determination,  only 
a  trace  of  chlorine  can  be  found,  whereas  the  methyl-orange  acidity 
is  almost  invariably  about  10%  of  the  total  acidity  and  is,  in  fact,  due 
to  the  fatty  acids  which  are  not  absolutely  neutral  to  methyl-orange. 
They  recommend  calculation  of  the  total  acidity  to  amyl  alcohol,  with 
the  reservation  that,  if  the  methyl-orange  acidity  much  exceeds  10  % 
of  the  whole,  a  gravimetric  estimation  of  chlorine  is  indicated.  The 
preferable  plan  would  be  to  add  to  the  number  of  c.c.  of  barium  hydrox- 
ide, required  in  the  second  (phenolphthalein)  stage  of  the  titration, 
one-ninth  or  the  actual  volume  required  in  the  first  (methyl-orange) 
stage,  whichever  is  the  least,  and  to  repeat  the  determination  if  the 
methyl-orange  acidity  much  exceeds  10  %  of  the  whole.  These  sug- 
gestions are  placed  in  a  note  and  not  in  the  text,  as  evidence  is  lack- 
ng  that  they  find  general  adoption.  The  use  of  both  indicators  is  ad- 
visable in  any  case,  as  a  check  is  thus  provided  on  the  manner  in  which 
the  analysis  has  been  carried  out. 

If  an  unexpectedly  high  value  for  higher  alcohols  is  found  and  the 
methyl-orange  acidity  is  normal,  there  is  always  a  suspicion  that  some 
of  the  ethyl  alcohol  has  remained  in  the  carbon  tetrachloride  extract  and 
been  oxidised  to  acetic  acid.  Schidrowitz  and  Kaye  (Analyst,  1905, 
30,  193)  say  that  though  some  ethyl  alcohol  is  certainly  extracted  and 
is  not  entirely  washed  out,  yet  this  in  their  experience  yields  but  little 
acetic  acid  and  is  mainly  converted  into  some  non-acidic  compound. 
It  is,  however,  easy  to  determine  the  mean  equivalent  of  the  acids  com- 
bined with  barium  hydroxide.  To  this  end,  the  neutralised  aqueous 
extract  is  separated  from  the  carbon  tetrachloride,  evaporated  to  dry- 
ness,  dried  at  130°  C.  and  weighed.  Let  the  weight  be:  a  mg.  and 
b  the  number  of  c.c.  of  baryta  consumed  in  determining  the  total 
(methyl-orange  and  phenolphthalein)  acidity,  supposing  the  methyl- 
orange  acidity  normal.  Then  the  mean  equivalent  of  the  acids  is 
given  by  10  £  —67 . 7.  The  equivalent  thus  determined  will,  as  a  rule, 
indicate  that  if  acetic  acid  is  present,  its  quantity  must  be  very  small. 
Where  the  methyl-orange  acidity  is  abnormally  high,  the  abnormal  part 
of  it  may  be  calculated  to  barium  chloride  first,  but  in  such  a  case  a 
repetition  of  the  whole  process  is  indicated. 

Crampton  and  Tolman  (7.  Amer.  Chem.  Soc.,  1908,  30,  98) 
recommend  the  use  of  an  oxidising  mixture  consisting  of  5  grm.  of 
potassium  dichromate  and  5  c.c.  of  sulphuric  acid  made  up  to  50  c.c. 


POTABLE    SPIRITS.  IQI 

with  water.     This  quantity  is  used  by  them  to  oxidise  the  higher 
alcohols  extracted  from  50  c.c.  of  whisky. 

Rose-Herzfeld  Method. — This  method,  as  slightly  modified  by 
Stutzer  and  K.  Windisch,  has  official  sanction  in  Germany.  It  depends 
on  the  increase  in  volume  of  chloroform  when  shaken  up  with  the  spirit 
under  certain  rigidly  defined  conditions.  For  measuring  the  increase 
in  volume  a  special  apparatus  is  supplied  by  dealers,  in  whose  cata- 
logues it  may  be  found  figured  and  described  as  a  " fusel-oil  tube." 
From  a  20  c.c.  bulb  springs  a  narrow  tube,  graduated  throughout  its 
length,  and  this  tube  is  surmounted  by  a  much  larger  bulb  which  is 
provided  with  a  stopper.  Several  modifications  of  the  tube,  differing 
in  the  range  and  fineness  of  the  graduations,  are  obtainable,  but  to 
be  of  any  service  they  should  show  0.02  c.c.,  and  be  readable  to  half 
this,  as  the  total  effective  reading  may  be  no  more  than  0.05  c.c. 
Alcohol,  absolutely  free  from  fusel  oil,  is  required  for  control  experi- 
ments; it  should  be  at  least  twice  fractionated  over  potassium  hy- 
droxide and  only  the  middle  fractions  taken.  For  use  in  the  test 
this  control  alcohol,  as  well  as  the  spirit  under  examination,  must  be 
freed  from  carbon  dioxide  by  boiling  under  a  reflux  condenser  and 
diluted  with  great  exactness  to  30%  alcohol  by  volume;  that  is 
to  say  the  sp.  gr.  must  lie  between  0.96555  and  0.96560.  The  apparatus 
is  next  charged  with  20  c.c.  of  a  mixture  of  fuming  and  ordinary  con- 
centrated sulphuric  acid,  rotated  so  that  the  whole  of  the  inner  surface 
is  wetted  by  the  acid,  gradually  warmed  up  and  finally  kept  for  an  hour 
in  a  water-bath  not  much  short  of  boiling.  It  is  then  rinsed  with 
distilled  water  and  dried  by  a  current  of  dry  air.  The  apparatus  is  then 
suspended  in  a  vessel  of  water  at  exactly  15°,  and  anhydrous  redis- 
tilled chloroform  (20  c.c.)  poured  in  down  a  thistle  funnel  which  extends 
nearly  to  the  bottom  of  the  apparatus ;  the  object  is  to  fill  with  chloro- 
form the  lower  bulb,  and  the  stem  up  to  the  lowest  graduation  mark, 
or  a  little  above  it,  without  wetting  the  upper  part  of  the  tube.  After 
beaving  the  chloroform  a  sufficient  length  of  time  to  insure  its  being 
at  exactly  15°,  its  level  is  exactly  adjusted  by  withdrawing  a  fraction 
of  a  drop  of  chloroform  by  means  of  a  long  capillary  tube. 
100  c.c.  of  the  exactly  30%  control  alcohol,  exactly  at  15°,  is 
then  introduced,  and  i  c.c.  of  sulphuric  acid  of  sp.  gr.  1.268.  The 
apparatus  is  stoppered,  turned  upside  down  so  that  the  contents  mix 
in  the  large  bulb,  and  shaken  vigorously  150  times  under  water,  the 
temperature  of  which  must  remain  15°.  The  apparatus  is  then 


IQ2  WINES   AND    POTABLE    SPIRITS. 

lifted  out  of  the  water  and  gently  inclined  so  that  the  chloroform  slowly 
trickles  back  into  the  lower  bulb;  in  this  way  a  sharper  line  of  separa- 
tion is  obtained.  The  apparatus  is  again  suspended  in  a  cylinder  of 
water  at  15°  and  after  an  hour  (not  sooner)  the  reading,  a,  taken 
where  the  two  layers  meet.  The  whole  process  is  next  repeated 
with  the  spirit  under  examination.  Let  the  reading  this  time  be  b. 
The  German  Public  Health  Department  multiplies  the  number  b-a 
by  2.22,  and  returns  the  result  as  parts  of  fusel  oil  per  100  c.c.  of 
absolute  alcohol  in  the  sample.  The  method  gives  results  limited 
in  accuracy  only  by  the  manner  of  graduation  of  the  instrument, 
when  applied  with  every  precaution  to  solutions  in  pure  spirit  of 
the  higher  alcohols  which  may  occur  in  fusel  oil.  Each  of  the 
alcohols  has  the  same  or  nearly  the  same  effect  on  the  chloroform,  but 
commercial  spirits  are  not  simply  alcoholic  solutions  of  higher  alcohols, 
and  the  actual  reading  is  the  algebraic  sum  of  the  readings  which 
would  be  given  by  each  constituent  of  the  spirit  singly.  Some  of  these 
constituents  may  cause  a  contraction  of  the  chloroform  column,  and 
Schidrowitz  (/.  Soc.  Chem.  Ind.,  1902,  21,  815)  has  stated  that  certain 
samples  of  whisky  actually  gave  negative  results  in  his  hands.  The 
method  is  described  at  length  in  all  German  text-books,  e.  g.,  in 
Maercker's  "Spiritusfabrication"  (ed.  Delbruck,  1903).  In  the  papers 
of  Schidrowitz  (loc.  cit.}  and  Veley  (/.  Soc.  Chem.  Ind.,  1906,  25, 
398)  those  interested  will  find  a  fairly  complete  set  of  references,  but 
little  encouragement  to  make  use  of  them. 

Sulphuric  Acid  Method. — This  method  has  official  sanction  in 
France.  Since  some  brandy  shippers  allege  that  it  more  often  con- 
firms their  palate  judgment  than  does  the  Allen-Marquardt  test,  it 
will  be  described  here  in  the  first  place  substantially  as  its  advocates 
describe  it  (cf.  Girard  et  Cuniasse,  U  Analyse  des  Alcools,  1899). 
The  criticisms  to  which  it  has  been  subjected  cannot  be  incorporated 
in  this  description,  since  they  are  not  helpful,  but  of  such  a  nature 
as  to  absolutely  discredit  the  method. 

50  c.c.  of  the  spirit,  which  by  previous  dilution  or  concentration 
has  been  brought  to  50  %  strength,  is  first  boiled  under  a  reflux 
condenser  with  some  reagent  which  will  fix  the  aldehydes,  i'  grm. 
of  metadiaminobenzene,  or  i  c.c.  of  syrupy  phosphoric  acid  and  i  c.c. 
of  aniline  (Mohler,  Ann.  Chim.  Phys.,  1891,  23,  129),  is  generally  used, 
but  Schidrowitz  and  Kaye  prefer  calcium  phenylhydrazine  sulphonate 
(Hewitt's  reagent),  and  this,  if  obtainable,  is  no  doubt  excellent  for  the 


POTABLE    SPIRITS.  193 

purpose.  A  few  pieces  of  pumice  are  added  and  the  whole  boiled  for  an 
hour.  After  cooling,  the  condenser  is  rearranged  for  distillation,  and 
the  spirit  distilled  until  45  c.c.  has  come  over.  The  distillate  is  made 
up  to  50  c.c.  with  distilled  water  and  10  c.c.  transferred  to  a  small  dry 
flask.  10  c.c.  of  the  purest  sulphuric  acid  obtainable  are  now  deliv- 
ered by  a  pipette  in  such  a  manner  that  the  acid  flows  down  the  side  of 
the  flask  and  reaches  the  bottom  without  much  mixing  with  the  spirit. 
The  contents  of  the  flask  are  then  well  shaken  and  left  for  an  hour  on 
the  water-bath.  Some  workers  heat  over  a  naked  flame  to  incipient 
boiling  and  then  allow  to  cool,  others  substitute  a  brine-bath  for  the 
water-bath.  After  cooling,  the  colouration  developed  is  compared 
with  that  given  under  the  same  conditions  by  a  standard  solution 
of  isobutyl  alcohol  in  pure  50%  ethyl  alcohol.  This  solution  is 
made  by  dissolving  exactly  0.5  grin,  of  pure  isobutyl  alcohol  in 
1000  c.c.  of  50%  ethyl  alcohol.  For  the  purpose  of  strict  com- 
parison 50  c.c.  of  this  solution  should  be  distilled  with  the  chosen 
de-aldehyding  reagent  and  the  first  45  c.c.  of  the  distillate  collected 
and  diluted  to  50  c.c.  10  c.c.  of  this  solution  are  treated  with  10 
c.c.  of  sulphuric  acid  and  heated  exactly  like  the  spirit  under  ex- 
amination. The  resulting  liquid  constitutes  the  colour  standard.  If 
the  tints  of  the  standard  and  of  the  assay  liquid  are  identical,  the  50  % 
spirit  under  examination  may  be  returned  as  containing  0.083  % 
of  higher  alcohols,  since  average  fusel  oil  is  said  to  develop  only 
0.6  of  the  colour  given  by  isobutyl  alcohol.  Results  are  more 
conveniently  returned  in  mg.  per  100  c.c.  of  absolute  alcohol, 
thus  a  sample  exactly  matching  the  standard  would  be  returned  as 
containing  167  mg.  per  100  c.c.  of  absolute  alcohol.  If,  as  is  usual,  the 
tints  of  the  standard  and  assay  liquid  differ,  it  is  necessary  to  compare 
them  accurately.  Numerous  special  colorimeters  have  been  devised 
with  the  object  of  facilitating  this  comparison,  but  it  is  to  be  noted  that 
the  colour  does  not  vary  directly  with  the  content  of  higher  alcohols, 
and  that  something  more  than  a  rule-of-three  sum  is  required  in  cal- 
culating the  results.  Suppose,  for  example,  that  a  layer  of  the  assay 
liquid  has  the  same  intensity  of  colour  as  a  layer  of  the  standard  only 
half  its  depth,  the  number  to  be  returned  is  not  83,  but  1 16  mg.  of  higher 
alcohols  per  100  c.c.  of  absolute  alcohol.  Girard  and  Cuniasse  (loc. 
«'/.)  give  a  curve  and  table  connecting  " apparent"  and  "real"  content 
of  isobutyl  alcohol,  but  as  this  is  only  a  secondary  constituent  of  fusel 
oil,  the  following  table  is  perhaps  more  useful. 
VOL.  1—13 


194  WINES   AND    POTABLE    SPIRITS. 

Ratio  of  intensity  of  colour  of  assay  Mg.  of  higher  alcohols  per  100  c  c. 

liquid  to  that  of  standard.  of  absolute  alcohol  in  sample. 

O-1  53 

0.2  77 

0.3  92 

0.4  105 

0.5  116 

0.6  127 

0.8  147 

i.o  167 

1.2  184 

1.4  2OI 

1.6  218 

1.8  235 

2.O  252 

The  above  table  is  calculated  from  the  curve  of  Girard  and  Cuniasse 
on  the  assumption  that  "average"  fusel  oil  produces  only  0.6  as  much 
colour  as  its  own  weight  of  isobutyl  alcohol  under  the  conditions  of  the 
test.  The  last  figure  of  each  of  the  numbers  in  the  right-hand  column 
has  no  justification,  but  the  writer  has  not  yet  met  with  any  chemist  who 
is  content  with  a  o  in  this  place.  "  Average"  fusel  oil  is  but  a  figment 
of  the  imagination.  The  proportions  of  the  higher  alcohols  present 
differ  with  the  raw  material  and  manner  of  distillation  of  the  spirit,  and 
each  one  has  its  own  capacity,  greater  or  less,  for  producing  colour  in  this 
test.  Experiment  shows  that  the  numbers  obtained  in  this  test  bear 
no  constant  relation  to  those  obtained  by  the  Allen-Marquardt  method, 
which,  whatever  its  imperfections,  is  based  on  scientific  principles. 
The  most  serious  criticism  to  which  the  test  has  yet  been  subjected, 
however,  is  that  of  Veley  (J.Soc.  Chem.  Ind.,  1906,  25,  400),  who  found 
that  isobutyl  alcohol  itself,  if  carefully  purified,  gives  no  colouration 
with  pure  sulphuric  acid.  The  reason  for  devoting  so  much  space  to 
so  unsatisfactory  a  test  has  been  already  given,  and  is  sufficient. 
Even  Veley  says  the  test  is  capable  of  giving  valuable  information. 
No  one  will  refuse  a  chemist  the  right  to  make  any  test  which  aids 
him  in  forming  a  judgment  regarding  a  sample,  but  if  the  number 
obtained  by  the  sulphuric-acid  test  is  returned  in  a  certificate  as  a 
measure  of  the  higher  alcohols,  it  is  reasonable  to  require  the  addition 
of  the  words  "colorimetric  method,"  since  the  colour  may  be  and 


POTABLE    SPIRITS.  195 

probably  is  the  measure  of  something  else  and  not  at  all  of  the  higher 
alcohols. 

It  has  already  been  said  that  the  Allen-Marquardt  method  is  the  only 
one  which  can  be  generally  recommended.  No  method  for  the  esti- 
mation of  such  a  variety  of  substances  as  is  included  under  the  head- 
ing of  " fusel  oil"  can  be  entirely  satisfactory,  and  .isopropyl  alcohol 
is  theoretically  not  estimated  by  the  Allen-Marquardt  method,  since 
on  oxidation  it  yields  acetone  and  no  acid.  Jenks  and  Bedford  (/. 
Soc.  Chem.  Ind.,  1907,  26,  123)  find  that  the  Allen-Marquardt  method 
greatly  underestimates  every  constituent  of  fusel  oil  except  amyl  al- 
cohol, and  they  have  devised  a  method  which  they  allege  enables  them 
to  differentiate  between  amyl  alcohols  on  the  one  hand  and  butyl 
and  propyl  alcohols  on  the  other,  but  little  experience  has  yet  been 
gained  with  the  method,  and  so  far  as  the  writer  knows  it  is  used  only 
by  its  authors. 

Acids  and  Esters. — 100  c.c.  of  the  spirit  is  distilled  until  only 
about  10  c.c.  remain;  distillation  is  then  continued  by  passing  in 
steam,  free  from  carbon  dioxide,  as  in  the  Allen-Marquardt  process 
for  the  estimation  of  higher  alcohols.  The  bulk  of  the  distillate 
should  be  about  150  c.c.  and  the  residue  left  in  the  flask  not  much 
more  than  5  c.c.  This  residue  may  be  diluted  with  water  and  the  fixed 
acid  determined  by  titration  with  N/ 10  alkali,  using  phenolphthalein 
as  indicator,  and  the  result  calculated  in  terms  of  tartaric  acid.  Only 
spirits  which  have  been  stored  long  in  wood  contain  any  appreciable 
amount  of  fixed  acid. 

The  distillate  contained  in  a  Jena  flask  is  exactly  neutralised  with 
sodium  hydroxide,  using  phenolphthalein  as  indicator,  and  the  volatile 
acid  calculated  as  acetic  acid,  though  higher  acids  are  certainly 
present  in  some  spirits.  A  further  10  c.c.  of  N/io  alkali  is  now 
added  and  the  whole  boiled  under  a  reflux  condenser  for  half  an  hour. 
After  cooling  10  c.c.  of  N/ 10  acid  is  added  and  then  N/ 10  alkali  to  ex- 
act neutralization.  The  amount  of  N/io  alkali  required  in  this  last 
titration  is  calculated  in  terms  of  ethyl  acetate,  though  more  complex 
esters  are  no  doubt  generally  present. 

Allen  preferred  to  remove  aldehydes  before  proceeding  to  the  esti- 
mation of  esters.  Though  this  is  desirable  on  theoretical  grounds, 
in  practice  the  error  involved  by  neglecting  the  action  of  the  aldehydes 
on  the  standard  alkali  is  very  small,  whereas  the  use  of  any  of  the 
dealdehyding  reagents  suggested  may  introduce  errors  of  unknown 


TQ6  WINES    AND    POTABLE    SPIRITS. 

magnitude.  Hewitt's  reagent  (sodium  or  calcium  phenylhydra- 
zine-^>-sulphonate)  is  the  least  objectionable  of  these  reagents,  but 
Hewitt  himself  (Analyst,  1905,  30,  153)  does  not  recommend  its  use 
in  this  connection. 

Bulletin  107,  (U.S.Dept.  of  Agric  )  recommends  that  after  distilling 
the  alcohol  over  sodium  hydroxide,  3  grm.  of  metaphenylenediamine 
should  be  added  and  the  mixture  allowed  to  stand  for  several  days  at 
room  temperatures  or  boiled  in  a  reflux  condenser  for  several  hours, 
then  distilled  slowly  rejecting  the  first  100  c.  c.  and  the  last  200  c.c. 

Furfural. — In  a  colourless  spirit  this  is  easily  estimated  by  com- 
paring the  tint  produced  in  the  liquid  by  the  addition  of  aniline  acetate 
with  that  produced  in  a  standard  solution  of  furfural  in  pure  50% 
alcohol.  The  alcohol  used  for  preparing  and  diluting  the  control  solu- 
tion must  be  free  from  aldehyde.  It  is  digested  with  potassium  hy- 
droxide and  fractionated,  and  only  the  portion  boiling  between  78°  and 
80°  collected.  If  this  gives  any  colouration  with  aniline  acetate,  the 
treatment  should  be  repeated  or  recourse  may  be  had  to  any  of  the 
de-aldehyding  reagents  already  mentioned.  In  the  reviser's  experience 
the  glacial  acetic  acid  supplied  to  analytical  chemists  never  contains  fur- 
fural or  even  traces  of  those  bodies,  present  in  commercial  acid,  which 
develop  a  yellow  colour  with  aniline.  It  is  convenient  to  boil  for  a 
few  minutes  equal  bulks  of  aniline,  acetic  acid  and  water.  The  mix- 
ture when  cool  constitutes  the  reagent,  and  the  boiling  effectually  de- 
stroys any  furfural  which  might  be  present  in  the  acid.  The  most  con- 
venient strength  for  the  control  liquid  is  0.05  grm.  furfural  per  1000  c.c. 
of  50  per  cent,  alcohol,  and  it  is  of  course  made  by  diluting  a  stronger 
solution.  Since  the  colouration  is  in  some  measure  dependent  on  the 
alcoholic  strength  of  the  liquid,  it  is  advisable,  when  the  spirit  under 
examination  differs  much  from  50%  strength,  to  dilute  the  con- 
trol liquid  with  water  or  pure  alcohol  until  its  alcoholic  content  approxi- 
mates that  of  the  sample.  To  20  c.c.  of  the  spirit  and  20  c.c.  of  the 
control  solution,  each  contained  in  Nessler  glasses,  i  c.c.  of  the  aniline- 
acetate  solution  is  added,  and  after  ten  minutes  the  tints  compared. 
Some  of  the  darker  solution  is  now  withdrawn  until,  on  looking  down 
the  tubes,  the  tints  appear  identical.  If  the  control  liquid  was 
diluted  to  adjust  its  alcoholic  content,  this  must  not  be  overlooked 
in  the  calculation,  which  is  otherwise  similar  to  that  .applied  in 
nesslerising. 

When,  as  is  usual,  the  spirit  has  considerable  colour,  this  must 


POTABLE    SPIRITS.  197 

in  some  manner  be  removed.  Hewitt  (/.  Soc.  Chem.  Ind.,  1902,  21, 
98)  recommends  distilling  nearly  to  the  last  drop,  adding  pure  dilute 
alcohol  to  the  distilling  flask,  and  again  distilling  nearly  to  the  last 
drop,  and  so  on  three  or  four  times.  The  united  distillates  are  then 
made  up  to  some  definite  volume.  Schidrowitz  (/.  Soc.  Chem.  Ind., 
1902,  21,  8 1 6)  strongly  criticises  this  procedure  mainly  on  the  ground 
that  furfural  may  be  formed  during  the  distillation.  He  prefers  to 
decolourise  as  far  as  possible  with  lead  acetate,  and  then  to  add  the 
aniline  reagent  to  the  liquid  under  examination  and  to  the  control. 
If  the  shades  (not  the  intensity  of  colour)  differ,  dilute  tincture  of  galls 
is  added  to  the  control  until  they  match.  The  tincture  of  galls  is  added 
after,  and  not  before,  the  reagent  because  it  is  intended  to  neutralise 
not  only  the  tint  remaining  in  the  spirit  after  treatment  with  lead  acetate, 
but  also  the  yellow  colour  which  certain  aldehydic  bodies  give  with 
aniline.  To  20  c.c.  of  the  sample,  Schidrowitz  adds  a  few  drops  of 
basic  lead  acetate  solution,  shakes,  adds  enough  saturated  potassium- 
sulphate  solution  to  precipitate  the  excess  of  lead,  filters  and  proceeds 
as  above  described. 

Aldehydes  other  than  furfural.     Many  methods  for  the  estimation 
of  aldehydes  in  potable  spirits  have  been  described.     The  only  one  in 
common    use,   however,  is    a    colorimetric  estimation  by  means  of 
Schiff's  reagent.     The  usual  formula  for  the  reagent  is: 
0.15  grm.  of  fuchsin  in  150  c.c.  of  water, 

•  ico  c.c.  of  sodium  hydrogen  sulphite  solution  (sp.  gr.  1.36), 
10  c.c.  of  concentrated  sulphuric  acid. 

As  the  presence  of  much  mineral  aci'd  greatly  reduces  the  sensibility 
of  the  reagent,  the  following  modification  is  recommended: 

0.2  grm.  rosaniline  base  is  dissolved  in  20  c.c.  of  a  cold  saturated 
solution  of  sulphurous  acid;  if  the  colour  is  not  discharged  after  24 
hours,  a  further  10  c.c.  of  sulphurous  acid  is  added;  after  a  further 
24  hours  the  colour  will  usually  be  discharged,  but  if  not,  more  sul- 
phurous acid  is  added  and  the  solution  when  finally  decolourised  is 
diluted  to  200  c.c.  with  water.  Some  samples  of  rosaniline  yield 
yellowish-brown  solutions  which  cannot  be  entirely  bleached,  but 
when  diluted  to  200  c.c.,  the  colour,  even  of  bad  samples,  is  sel- 
dom of  serious  account. 

A  control  solution  of  acetaldehyde  in  pure  50  %  alcohol  is  re- 
quired. A  convenient  strength  is  0.2  grm.  acetaldehyde  per  1000  c.  c. 
The  alcohol  must  be  freed  from  aldehyde  similarly  to  that  used  in  pre- 


198  WINES    AND    POTABLE    SPIRITS. 

paring  the  furfural  control.  It  is  convenient  to  prepare  a  stock  which 
reacts  neither  with  Scruff's  reagent  nor  with  aniline. 

Bulletin  107,  U.  S.  Dept.  of  Agriculture,  gives  the  following  as 
a  provisional  method  for  preparing  a  standard  aldehyde  solution. 
Grind  aldehyde  ammonia  in  a  mortar  with  ether  and  decant  the 
ether,  repeating  this  operation  several  times;  then  dry  the  purified 
material,  first  in  a  current  of  air  and  then  in  vacuum  over  sulphuric 
acid.  Dissolve  1.386  grm.  of  this  substance  in  50  c.c.  of  95%  alcohol, 
purified  from  aldehyde;  to  this  solution  add  22.7  c.c.  of  N/i  sulphuric 
acid,  made  with  alcohol  instead  of  water,  make  up  to  TOO  c.c.  and  add 
0.8  c.c.  to  compensate  for  the  volume  of  the  ammonium  sulphate 
precipitate.  Let  the  liquid  stand  overnight  and  then  filter.  The 
solution  contains  i  grm.  of  aldehyde  in  100  c.c.  and  keeps  well. 

The  most  convenient  standard  is  prepared  by  adding  2  c.c.  of  the 
above  solution  to  100  c.c.  of  50%  (by  volume)  of  alcohol;  i  c.c.  of 
this  dilute  solution  contains  0.0002  grm.  aldehyde.  This  dilute 
solution  does  not  keep. 

The  test  is  carried  out  by  adding  to  20  c.c.  of  the  liquid  under  exami- 
nation and  to  20  c.c.  of  the  control  solution,  5  c.c.  of  the  reagent, 
and  comparing  the  tints  produced  after  20  minutes.  Portions  of  the 
darker  are  withdrawn  until,  on  looking  down  the  tubes,  the  tints  appear 
equal.  Dubosc's  or  other  colorimeter  is  used  by  those  who  make 
many  of  these  determinations,  but  the  chemist  in  general  practice  may 
use  Nessler  glasses,  and  calculate  on  the  assumption,  not  quite  true, 
that  the  intensity  of  colour  is  proportional  to  the  amount  of  aldehyde 
present.  The  influence  of  furfural  may  be  neglected,  since  it  gives 
a  very  faint  colouration  with  Schiff 's  reagent,  compared  with  that  given 
by  acetaldehyde.  It  is  desirable  that  the  solution  under  examina- 
tion and  the  control  solution  should  be  of  approximately  the  same  alco- 
holic strength,  and  this  is  effected  by  adding  to  one  or  other  of  them 
water  or  pure  alcohol. 

Highly  coloured  spirits  are  best  treated  by  Schidrowitz's  method, 
described  under  Furfural.  The  spirit  is  decolourised  as  far  as  possible 
with  basic  lead  acetate,  the  excess  of  the  latter  removed  by  the  addition 
of  potassium  sulphate,  and  the  liquid  filtered.  The  control  is  then 
coloured  with  tincture  of  galls  until  it  exactly  matches  the  sample, 
Schiff's  reagent  added  to  both  control  and  assay  liquid  and  the  com- 
parison made  after  20  minutes. 

Non-volatile  Residue. — This  is  sometimes  of  importance.     When 


POTABLE    SPIRITS.  IQ9 

freshly  distilled,  spirits  contain  no  trace  of  non-volatile  matter.  When 
kept  in  casks  they  take  up  more  or  less  fixed  matter,  but  the  amount 
rarely  exceeds  100  grains  per  gallon.  The  fixed  matter  may  include, 
among  other  substances,  tannin,  colouring  matter,  sulphates  and  traces 
of  sugar.  The  proportion  of  non-volatile  matter  in  spirits  is  ascer- 
tained by  evaporating  50  or  100  c.c.  to  dryness  on  a  water-bath. 
Some  indication  of  its  nature  may  be  obtained  by  tasting  the  residue. 
On  ignition  in  the  air,  any  zinc,  lead,  or  copper  present  in  the  spirit 
will  be  left  as  an  oxide.  Very  sensible  traces  of  these  metals  may  be 
present  accidentally,  and  there  is  good  evidence  that  their  salts  were 
in  the  past  occasionally  used  as  adulterants.  Occasionally,  clarifying 
materials  containing  lead  acetate  have  been  employed.  Alum  was 
also  used  occasionally.  The  reaction  of  the  ignited  residue  should  be 
observed,  as,  if  alkaline,  an  alkaline  carbonate,  acetate,  tartrate,  etc., 
must  have  been  present. 

Sulphates  will  be  detected  on  adding  barium  chloride  to  the  diluted 
spirit.  Free  sulphuric  acid  has  been  met  with  in  whisky,  and  is 
said  to  have  been  used  formerly  for  adulterating  gin.  This  is  ex- 
tremely improbable.  The  presence  of  free  sulphuric  acid  may  be 
detected  by  the  methods  used  for  examining  vinegar  for  mineral  acids. 

Tannin  is  often  present  in  brandy,  being  chiefly  extracted  from 
the  casks  used  for  storing.  Sometimes  it  is  purposely  added  in  the 
form  of  tincture  of  galls  or  oak-bark.  It  may  be  detected  by  the  dark- 
.ening  produced  on  adding  ferric  chloride  to  the  spirit,  and  any  reaction 
thus  obtained  may  be  confirmed  by  boiling  off  the  alcohol  from  another 
portion  of  the  spirit  and  adding  solution  of  gelatin  to  the  residual 
liquid,  when  a  precipitate  will  be  produced  if  tannin  be  present. 

A  few  analyses  of  spirits  are  given  here,  not  to  serve  as  " types" 
nor  to  prove  the  folly  of  referring  spirits  to  types,  but  to  give  some 
idea  of  the  results  to  be  expected.  Girard  and  Cuniasse,  at  the  end 
of  their  book  and  elsewhere,  have  published  a  large  number  of  spirit 
analyses;  the  most  interesting  of  their  numbers  are  those  which  relate 
to  brandy,  but  they  give  several  examples  of  French  industrial  alcohol. 
Probably  the  whiskies  selected  by  Schidrowitz  (/.  Soc.  Chem.  Ind., 
1902,  21,  818)  are  more  typical  of  the  spirit  consumed  in  Great  Britiain 
than  are  the  whiskies  on  which  continental  chemists  report  from  time 
to  time.  Vasey  (Analysis  of  Potable  Spirits,  London,  1904)  gives 
a  number  of  analyses,  some  from  continental  sources  but  many  original, 
while  in  Konig's  "Chemie  der  menschlichen  Nahrungs-  und  Genussmit- 


20O 


WINES   AND    POTABLE    SPIRITS. 


tel"  there  are  many  more.  Reference  to  Vasey  may  lead  the  analyst  to 
suppose  that  the  judgment  of  spirits  is  comparatively  simple,  and 
Girard  and  Cuniasse  appear  to  base  confident  judgments  on  ana- 
lytical data,  but  some  of  their  own  selected  analyses  invalidate  the 
standards  they  suggest.  Both  Vasey  and  Girard  and  Cuniasse,  it  is 
true,  assume  that  the  analyst  will  call  on  his  palate  to  aid  him  in  his 
judgment,  but  they  may  fairly  be  quoted  as  representing  the  school 
which  believes  most  strongly  in  the  ability  of  the  chemist,  qua  chemist, 
to  decide  whether  spirits  are  "genuine"  or  otherwise.  As  a  corrective 
to  too  great  confidence  in  numbers,  the  analyst  may  be  referred  to  a 
communication  by  Windisch  (Zeit.  Unters.  Nahrungs-  und  Genussm., 
1904,  8,  465)  and  to  a  paper  on  " Brandy,"  by  Hehner  (Analyst,  1905, 
30,  36)- 

RESULTS  OF  ANALYSES  OF  POTABLE  SPIRITS. 


Milligrams  per  100  c.c. 

of  absolute  alcohol. 

Alcohol 
per  cent. 

Aldehydes 

by  vol. 

Higher    Esters 

Acid. 

Furfural. 

excl. 

alcohols. 

furfural. 

i.   Brandy,     genuine     grape,     2 

years. 

64  .  4 

253 

136 

77 

i  .  3 

19 

2.   Brandy,    genuine    grape,     16 

years  

61.1 

95 

81 

59 

I  .0 

24 

3.   Brandy,     genuine    grape,     35 

years  

47-5 

345 

133 

202 

I  .2 

48 

4.   Brandy,   admittedly    blended 

with  patent  spirit  
5.   "  Brandy,  '  admittedly  flavour- 
ed patent  spirit  (no  grape).  . 

SO.D 
50.0 

60               67 
18              32 

58 

19 

0.9 

O  .  2 

18 
6 

6.  Sold  as  "  cognac  "  

64  .0 

Nil 

14                II 

0.3         i                   2 

7.  Whisky,  malt,  new  

62.8 

189              70             16 

4.4        !               II 

8.   Whisky,  malt,  4  years  
9.  Whisky,  grain,  new  

60.5 
61.5 

217 
76 

95              55 
48            Nil 

3Nfl 

23 
5 

10    Whisky,  grain,  4  years  

59-7 

77 

77 

II 

Nil 

ii 

1  1    Rum   Jamaica  genuine 

69.5 

94 

440            176 

2  -9 

22 

12.  Rum  admittedly  blended  with 

patent  spirit  

36-° 

114 

83            127 

0.9 

II 

1  3.  Sold  as  "  rum  "  

s  ?  .0 

8 

45               65 

0.6 

6 

14.  Gin  

45 

37             Nil 

Nil 

2 

15.  Highly  rectified  spirit  i                            3 

3               3 

Nil                  o.i 

Brandy  is  usually  defined  as  a  spirituous  liquid,  distilled  from  wine 
and  matured  by  age.  The  best,  that  is  the  most  palatable  and  valu- 
able brandies,  are  no  doubt  produced  in  this  way,  but  it  is  difficult, 
if  not  impossible,  for  a  chemist  to  decide  with  certainty  whether  a 
particular  sample  of  "brandy"  is  properly  so  described.  It  is  true 
that  on  the  average  brandies  contain  80  to  100  mg.  of  esters  per 
100  c.c.  of  absolute  alcohol,  and  that  some,  including  some  of  the 
finest,  contain  much  more,  but  some  genuine  wine  brandies  contain 


POTABLE    SPIRITS.  2OI 

less  than  half  this  amount,  and  there  is  nothing  to  prevent  a  distiller 
from  obtaining  pure  alcohol  from  wine  except  the  consideration  that 
pure  alcohol  is  flavourless  and  not  saleable  at  the  price  obtained  for 
less  pure  distillates.  On  the  other  hand,  except  as  regards  the  all- 
important  flavour,  there  is  no  difficulty  in  producing  a  spirit,  innocent 
of  grapes,  but  complying  with  any  of  the  standards  which  have  been 
laid  down.  A  little  rum,  with  400  ing.  esters  per  100  c.c.  will  supply  the 
necessary  esters  to  a  large  bulk  of  silent  spirit  and  so  on  with  other 
constituents.  The  sum  of  the  higher  alcohols,  esters,  acid,  aldehydes 
and  furfural  is  usually  over  300  mg.  per  100  c.c.  of  absolute  alcohol, 
but  it  is  generally  agreed  now  that  no  rules  can  be  laid  down  for  this 
total  which  was  formerly  spoken  of  as  the  "coefficient  of  impurities." 

Nor  is  it  easy  to  decide  on  the  age  of  brandy  or  other  spirit.  Some 
oxidation  with  formation  of  aldehyde  and  acid  is  to  be  expected  and 
the  increased  acid  determines  some  further  esterification,  but  as  spirits 
start  with  such  widely  different  compositions  it  is  possible  for  one 
2o-year-old  brandy  to  be  indistinguishable  analytically  from  a  new 
brandy  from  another  still.  No.  2  is  a  case  in  point.  The  low  ester 
number,  which  would  cause  some  to  doubt  the  age  of  this  sample,  is 
no  doubt  due  to  the  manner  of  storage  which  was  such  that  compara- 
tively little  oxidation  took  place  with  consequent  small  increase  of  the 
acidity  on  which  the  degree  of  esterincation  probably  depends.  It  is 
highly  improbable  that  any  distiller  of  genuine  grape  brandy  would 
deliberately  refine  his  product  so  as  to  get  an  article  like  No.  6,  but  the 
figures  given  do  not  prove  that  the  spirit  was  other  than  brandy  as  de- 
fined by  the  British  Pharmacopoeia. 

Whisky. — A  Royal  Commission  is  engaged  in  hearing  evidence 
as  to  what  whisky  should  be.  Like  other  potable  spirits  it  is  more 
or  less  aqueous  alcohol,  containing  a  small  proportion  of  other  matters 
which  give  it  the  characteristic  flavour  associated  with  the  name ;  flavours, 
perhaps,  would  be  more  correct,  since  several  types  of  whisky  are  dis- 
tinguished by  makers  and  drinkers  of  the  beverage.  It  may  be  derived 
exclusively  from  malt  and  distilled  in  the  comparatively  simple  pot 
still,  or  mainly  from  raw  grain  and  distilled  in  a  patent  still  which  is 
capable  of  bringing  about  very  complete  rectification.  The  whisky 
distiller  does  not  work  his  patent  still  so  as  to  bring  about  the  maxi- 
mum degree  of  rectification  of  which  it  is  capable,  and  in  pot-still 
distillation  about  two-thirds  of  the  total  volatile  impurities  are  elimi- 
nated with  the  pot  ale  and  spent  lees,  so  that  the  difference  between  pot 


202  WINES   AND    POTABLE    SPIRITS. 

still  and  patent  spirits  is  not  necessarily  so  great  as  is  sometimes  sup- 
posed. It  is  incorrect  to  speak,  as  was  done  in  the  last  edition  of  this 
work,  of  the  pot  still  as  an  apparatus  in  which  little  or  no  fractionation 
occurs,  but  equally  incorrect  to  lay  stress  on  the  temporary  separation 
of  the  distillate  into  three  fractions  as  do  Schidrowitz  and  Kaye  (/. 
Inst.  Brew.,  1906,  12,  496).  Of  these  fractions  the  first  and  last  are 
added  to  the  next  charge  to  recover  the  alcohol  contained  in  them,  and 
the  only  certain  measure  of  impurities  eliminated  is  the  amount  con- 
tained in  the  pot  ale  and  spent  lees,  which  with  whisky  are  the  sole 
ultimate  products  of  pot-still  distillation.  Schidrowitz  and  Kaye  have 
shown  that  the  esters  of  the  foreshots  and  feints  may  be  partially  hydro- 
lysed  on  repeated  distillation,  and  that  aldehyde  may  be  oxidised  to 
the  much  less  volatile  acetic  acid  is  probable,  but  their  figures,  based 
on  a  single  run,  scarcely  justify  their  conclusion  that  only  10%  of  the 
total  impurities  find  their  way  into  pot-still  whisky;  in  fact,  they  may 
equally  well  be  made  to  support  an  estimate  of  30%. 

A  large  proportion  of  the  whisky  sold,  and  approved  by  its  purchasers, 
is  a  blend  of  grain  whisky  containing  notably  less  impurities  than  Nos.  9 
and  10  with  a  pot-still  whisky  containing  notably  more  impurities  than 
Nos.  7  and  8. 

AMERICAN  WHISKY  is  the  subject  of  a  special  paper  (/.  Amer. 
Chem.  Soc.,  1908,  30,  98)  by  Crampton  and  Tolman,  who  show  that 
its  composition  may  range  within  wide  limits.  Thirty  whiskies 
were  examined  and,  what  is  more  important,  were  preserved  in 
bonded  warehouses  in  barrels,  which  were  opened  once  a  year  for 
8  years  and  a  sample  from  each  withdrawn  and  analysed.  No  such 
thorough  investigation  into  the  effects  of  long  storage  in  wood  has 
been  made  before,  and  if  it  is  said  that  no  new  information  has  been 
brought  to  light,  the  answer  is  that  this  investigation  transforms 
into  facts  what  were  previously  no  more  than  reasonable  hypotheses. 
The  result  of  this  investigation  is  to  establish  the  following  facts 
Water  passes  more  easily  than  alcohol  through  the  pores  of  the  wood, 
with  the  result  that  the  alcoholic  strength  of  spirits  stored  in  wood 
increases  about  i%  per  annum.  The  increase  in  the  percentage  of 
higher  alcohols  with  age  is  entirely  explained  by  the  diffusion  of  water 
and  ethyl  alcohol  through  the  pores  of  the  wood,  which  appears  to  be 
practically  impervious  to  the  higher  alcohols.  The  other  ''impurities" 
do  actually  increase  in  amount,  the  increase  being  comparatively 
rapid  during  the  first  3  or  4  years  and  after  that  proceeding  very 


POTABLE    SPIRITS.  203 

slowly.  The  work  of  Crampton  and  Tolman  also  establishes  the 
fact  that  the  source  of  furfural  in  whisky  is  two-fold;  it  may  be  derived 
from  the  grain  of  the  mash  or  from  the  charred  wood  of  the  barrel. 
The  aroma  and  flavor  of  the  whisky  are  derived  from  the  charred 
interior  of  the  barrel. 

Rum,  especially  Jamaica  rum,  is  usually  characterised  by  its  high 
content  of  esters  and  volatile  acid  and  by  its  flavour. 

Gin  is  made  by  flavouring  highly  rectified  spirit  with  oil  of  juniper 
berries  or  other  substances,  with  or  without  the  addition  of  sugar. 
Previous  to  sale  the  gin  is  broken  down  considerably  by  addition  of 
water. 


YEAST. 


BY  EMIL  SCHLIGHTING. 

Yeast  is  an  organized  ferment,  belonging  to  a  class  of  fungi  grouped 
botanically  as  ''budding  fungi"  and  generally  characterized  by  their 
faculty  of  causing  alcoholic  fermentation  in  a  saccharine  solution  and 
by  their  mode  of  propagation  by  "budding,"  although  at  times  prop- 
agation by  fission  has  been  observed. 

The  yeast  fungi  constitute  the  genus  "Saccharomyces,"  which  is 
again  subdivided  into  many  species.  The  Saccharomycetes,  or  yeast 
fungi  having  the  distinctive  faculty  of  forming  endospores,  are  the 
only  and  most  important  ones  for  the  fermentation  industry,  while 
all  other  yeasts  and  many  Saccharomycetes  are  of  no  value  to  the 
industry  and  arts;  in  fact,  some  of  these  are  frequently  detrimental. 
The  yeast  plant  is  abundantly  distributed  thoughout  the  vegetable 
kingdom  and  in  the  air. 

Physical  Appearance. — Observed  in  the  distillery  and  brewery,  it 
forms  a  pale  yellowish-white  frothy  mass  with  a  peculiar  ethereal  odor 
and  generally  bitter  taste.  The  brewer  distinguishes  between  top  and 
bottom  fermenting  yeast;  the  former  acts  at  temperatures  of  18°  to  25° 
and  appears  at  the  surface  of  the  liquid  while  the  latter  ferments 
at  temperatures  from  4°  to  10°  and  settles  at  the  bottom  of  the  fer- 
menting liquid. 

Microscopical  Structure. — Examined  under  the  microscope,  yeast 
appears  in  the  form  of  many  small  cells  of  7  to  TO//  in  diameter. 

They  are  seen  as  either  single  cells  or  colonies;  their  shape  differs  with 
the  various  species  from  a  round  to  oblong,  sometimes  elliptical  form, 
but  even  this  variation  of  form  occurs  in  the  same  species,  so  that,  ac- 
cording to  Hansen,  a  grouping  or  differentiation  of  species  by  this 
means  alone  becomes  almost  impossible.  The  yeast  cell  consists  of  a 
colourless  cell  wall  with  equally  colourless  cell  contents;  the  latter 
consisting  of 

a.  Protoplasm, 

b.  Nucleus, 

c.  Vacuoles,  and 

d.  Some  other  granular  enclosures  of  various  description. 

205 


CELL    CONTENTS.  2Oy 

fated  by  a  5%  borax  solution  similar  to  plant  gelatins;  this  is 
utilized  in  practice  for  facilitating  the  settling  and  pressing  of  yeast 
by  the  addition  of  borax.  Will  considers  the  formation  of  this  network 
due  to  a  gelatinization  of  the  cell  membrane,  the  protein  content  also 
taking  an  active  part.  The  exact  constitution  and  formation  of  this 
network  under  certain  conditions  and  in  various  yeasts  have  not  been 
established,  but  former  investigators,  i.  e.,  Nageli  and  Pasteur,  have 
attributed  to  yeast  the  faculty  of  separating  and  excreting  protein 
bodies  or  peptones. 

Cell  Contents. — The  cell  nucleus  is  difficult  to  distinguish  in  the 
living  cell.  It  may  be  made  visible  by  staining.  It  is  generally 
spherical,  sometimes  disc-shaped.  Its  diameter  is  about  1/3  of  the 
whole  cell. 

According  to  investigations  of  Janssens  and  Leblanc,  there  exists 
only  one  nucleus  in  each  cell.  Dangeard,  Janssens  and  Wager  assert 
that  it  encloses  a  nucleolus  or  granular  body,  possessing  a  membrane. 
The  intermediate  space  consists  of  a  fine  network  of  granular  proto- 
plasm. At  the  end  of  fermentation,  at  a  stage  of  exhaustion,  vacuoles 
appear  filled  with  a  fluid  of  unknown  composition,  differing  from 
protoplasm  in  lower  refraction.  They  sometimes  occupy  the  largest 
portion  of  the  cell  and  also  contain  crystalline  enclosures.  Frequently 
they  have  been  observed  to  contain  very  small  granular  bodies  which 
are  in  constant  motion  (Brownian  movement).  Kiister  considers 
them  decomposition  products  of  protoplasm  of  a  semi-liquid  consistency 
which  eagerly  absorb  stains. 

Strange  refractive  bodies  are  often  seen  in  the  protoplasm,  appearing 
generally  at  the  end  of  fermentation;  these  were  formerly  considered 
as  oil  drops;  they  are  now  called  granules;  their  number  and  size  differ 
considerably  in  the  various  cells;  they  are  at  times  round  and  then 
angular.  According  to  Will,  their  membrane  consists  of  proteid 
matter,  with  a  similarly  constituted  interior  network;  their  contents 
are  of  a  fatty  nature;  as  it  may  be  removed  by  fat-dissolving  reagents 
(ether,  chloroform,  alkalies,  alcohol,  petroleum  spirit).  The  proteid 
cell  wall  is  dissolved  by  concentrated  sulphuric  acid,  the  oily  drops 
flow  together,  and  color  first  green,  then  bluish-green  and  finally 
black.  Absolute  alcohol  added  to  yeast  causes  the  cells  to  shrink, 
and  they  are  soon  killed.  Dead  cells  are  generally  distinguished  from 
live  ones  by  their  greater  absorbing  faculty  and  ease  of  staining  ' 

Chemical  Composition  of  Yeast. — The  percentage  composition 


208  YEAST. 

of  yeast  shows  only  very  slight  differences  in  the  analyses  of  top  and 
bottom  yeasts.  The  nitrogen  is  usually  somewhat  higher  in  top  yeast, 
but  generally  the  composition  will  depend  on  the  nutrition.  Accord- 
ing to  Mitcherlich,  Schlossberger,  Dumas,  Wagner  and  Liebig,  the 
ash-free  dry  substance  of  yeast  has  the  following  composition: 

Carbon       Hydrogen       Nitrogen 
Top  Yeast,  48.64          6.76  11.46 

Bottom  Yeast,         44.99          6.72  8.73 

Older  yeast,  according  to  Schlossberger,  is  generally  somewhat 
poorer  in  nitrogen,  owing  to  decomposition  of  its  cell  contents. 

The  moisture  ranges  from  75  and  83  %. 

The  sulphur  ranges  from  0.39  and  0.69  %.     (Liebig). 

Ash  of  Yeast. — Investigators  differ  considerably  in  their  results 
regarding  the  ash  content.  This  is  stated  for  top  yeast  to  be  from  2.5 
to' 1 1.5%;  for  bottom  yeast  from  3.5  to  10.1%.  yeast.  Too  much  re- 
liance, however,  cannot  be  placed  upon  these  figures,  as  the  original 
materials  for  analysis  were  not  uniform  or  have  not  been  stated.  The 
ash  is  stated  to  consist  of  phosphates,  sulphates,  silicates,  chlorides 
and  potassium,  sodium,  magnesium,  and  calcium;  potassium  phos- 
phate constituting  the  largest  proportion. 

Nitrogenous  Constituents. — Mostly  proteins;  Schlossberger  ex- 
tracted with  potassium  hydroxide  a  substance  containing  13.9% 
nitrogen,  Mulder  obtained  with  dilute  acetic  acid  a  substance  with 
16%  nitrogen,  and  Nageli  and  Loew  found  in  a  bottom  yeast  with  8% 
nitrogen  as  follows:  Albumin,  36%;  glutin-casein,  9%;  peptones, 
2%.  The  nuclein  bodies,  forming  the  main  constituents  of  the  cell 
nucleus  have  been  studied  closely  and  were  isolated  by  Kossel,  and 
their  presence  proved  by  Hoppe-Seyler.  Stutzer  found  in  a  beer 
yeast  having  8.65%  nitrogen,  2.26%  present  as  nuclein. 

The  protein-like  substance  formed  by  the  action  of  dilute  alkalies 
upon  nuclein  resists  the  action  of  pepsin  and  trypsin.  Other  protein 
bodies  not  yet  clearly  defined  are  thought  to  form  a  gelatinous  net- 
work around  the  cells ;  these  are  also  partly  transferred  to  the  beer  and 
aid  in  the  retaining  of  larger  amounts  of  carbonic  dioxide.  Reichard 
maintains  that  these  gelatinous  bodies  are  indispensable  for  the  pro- 
duction of  a  fine,  creamy  foam  in  beer. 

Fat. — The  fat  content  fluctuates  with  the  nutrition  of  the  yeast. 
Nageli  and  Loew  state  it  to  be  about  5  %.  It  consists,  according  to 


CARBOHYDRATES    OF    YEAST.  2OQ 

Darexy  and  Gerard,  mainly  of  stearic  and  palmitic  acids  and  a  little 
butyric  acid,  partly  as  glycerides,  partly  free.  It  serves  as  a  reserve 
food  material.  Lecithin  and  cholesterol  have  also  been  isolated 
from  yeast  by  Hoppe-Seyler. 

Carbohydrates  of  Yeast. — 

The  following  have  been  isolated: 

1.  Glycogen. 

2.  Yeast-pectose. 

3.  Yeast-cellulose. 

Yeast-glycogen  was  first  obtained  by  Cremer  (1894),  who  proved 
it  to  be  identical  with  the  glycogen  of  the  liver.  The  dry  substance  of 
yeast  contains  between  31  and  32%  of  glycogen;  its  percentage  may 
be  increased  by  suitable  nourishment.  Contrary  to  the  claim  of 
Laurent,  glycogen  cannot  be  absorbed  and  assimilated  from  nutrient 
solution  by  yeast.  Henneberg  asserts  that  the  various  types  of  yeast 
can  be  distinguished  by  the  extent  of  glycogen  formation. 

According  to  investigations  made  by  Cremer,  and  later  confirmed 
by  Buchner  and  Rapp,  yeast  also  contains  an  enzyme  capable  of 
converting  glycogen  into  a  glucose.  "  Yeast  gum"  or  yeast  pectinous 
substances  have  been  isolated  by  several  investigators. 

Yeast  cellulose  or  substances  resembling  cellulose  are  contained  in 
the  membrane  of  the  cell.  This  cellulose  behaves  differently  from 
ordinary  pure  cellulose;  is  insoluble  in  ammoniacal  cupric  hydroxide 
and  gives  none  of  the  usual  cellulose  reactions.  Salkowski  obtained 
by  extraction  with  a  3  %  potassium  hydroxide  a  substance  resembling 
cellulose,  having  a  constitution  of  C6H10O5;  boiled  in  water  it  was 
split  into  a  soluble  substance  giving  a  red  color  with  iodine,  and  an- 
other insoluble  jelly-like  substance.  The  former,  so-called  erthyro- 
cellulose,  gave  on  hydrolysis  only  dextrose,  while  the  latter  resulted 
into  achroocellulose  and  a  small  amount  of  mannose. 

Payen  states  cellulose  to  be  present  in  dry  yeast  up  to  29.4%. 
Liebig  and  Pasteur  found  only  16  to  18%. 

Tannin. — Jorgensen  claims  the  presence  of  tannin  in  yeast  during 
the  first  stages  of  fermentation,  but  Naumann  and  Will  were  not 
able  to  find  it. 

Mineral  Constituents  of  Ash. — There  are  many  analytical  data 
by  different  authorities  regarding  the  ash  constituents  of  yeast  and 
they  generally  are  found  to  range  between  the  following  limits: 
VOL.  1—14 


210  YEAST. 

Potassa  (K2O)  Soda   (Na2O)  Magnesia  (MgO)  Lime  (CaO) 

23-3  to  39.5  0.5  to  2.5  4.1  to  6.5  i.o  to  7.6 

Phosphoric  Acid  (P2O5)  Sulphuric  Acid  (SO 0    Silica  (SiO2)  Chlorine 

44.8  to  59.4  0.3  to  6.4  0.9  to  1.9  0.03  to  o.i 

Vitality  of  Yeast. — According  toHansen,  yeasts  retain  their  vitality 
longest  in  a  10%  sucrose  solution.  Of  44  species  after  20  years' 
observation  only  3  varieties  died  in  this  solution.  They  die  quicker 
in  wort,  also  in  water,  but  generally  keep  for  a  period  of  several 
months  to  years.  Drying  in  a  very  finely  divided  state  kills  yeast  after 
a  few  days;  some  varieties  may  live  for  several  months;  spores  are 
more  resistant.  Dried  on  filter  paper  or  cotton,  yeast  may  retain  its 
vitality  for  at  least  one  year;  spores  two  or  three  years.  Will  made 
thorough  and  successful  experiments  by  drying  yeast  with  powdered 
wood  charcoal;  the  yeast  was  still  alive  after  10  years. 

Heat. — Moist  heat  is  detrimental  to  yeast,  and  kills  it  between  50 
and  60°;  spores  are  more  resistant.  In  a  wine  with  6.4%  alcohol  the 
yeast  cells  were  killed  after  heating  at  45°  for  2  hours.  Cooling  to 
—130°  and  freezing  for  months  is  not  detrimental  to  the  yeast  cells. 

Light. — Diffused  daylight  and  electric  arc  light  retard  the  budding; 
sunlight  kills  the  cells.  It  is  not  known  whether  yeasts  also  participate 
in  the  detrimental  action  of  sunlight  upon  the  taste  and  odor  of  beer. 

Characterisation  of  Saccharomycetes. — If  brought  into  saccha- 
rine fermentable  solutions,  yeast  will  form  a  sediment  which  increases 
with  the  period  of  fermentation;  in  breweries  and  distilleries  this  con- 
sists mostly  of  round  or  oval  cells.  Such  yeasts  are  classed  as  the 
Saccharomyces  cerevisice  type. 

Wine  yeasts  and  some  other  types  are  elliptical,  and  are  classed, 
according  to  Rees,  as  the  Ellipsoideus  type.  A  third  type,  called 
Pastorianus,  is  characterized  by  its  elongated  sausage-shaped  form. 
These  latter,  Pastorianus  yeasts,  are  generally  detrimental  to  the  fer- 
mentation process  and  are  considered  as  disease  ferments. 

Although  the  cells  of  one  type  are  not  always  strictly  uniform,  there 
exist  for  the  most  part  a  larger  number  of  characteristic  cells  enabling 
positive  identification. 

Spore  Formation. — Besides  vegetative  propagation  by  budding, 
the  Saccharomycetes  cells  also  form  endospores,  the  cell  being  trans- 
formed into  an  ascus.  Hansen  has  used  the  different  spore  formation 
and  its  properties  to  differentiate  between  the  various  types  of  culture 
and  wild  yeasts.  The  spores  of  culture  yeasts  appear  to  be  empty, 


CARBOHYDRATES    OF    YEAST.  211 

while  the  spores  of  wild  yeast  are  strongly  refractive.  These  phenomena 
are  utilized  in  the  analysis  of  brewery  yeast. 

Enzymes. — The  yeast-cell  contains  many  enzymes  distinct  from 
each  other  in  their  respective  action.  The  kind  and  number  of  en- 
zymes in  different  types  differ  materially  and  may  be  considered  as 
one  of  the  safest  and  most  constant  factors  of  identification  and 
differentiation. 

Some  of  these  enzymes  have  the  faculty  of  diffusing  through  the 
cell  membrane;  others  are  partly  incapable  of  diffusion  and  are  then 
utilized  for  assimilation  and  disassimilation  within  the  cell.  Hahn 
proposes  for  these  enzymes  the  name  "endoenzymes." 

A  synthetic  action  of  yeast  enzymes  has  only  been  proved  for  "  yeast 
glucase"  by  Croft  Hill  and  Emmerling,  the  final  product  from  dextrose 
being  maltose,  according  to  Croft  Hill,  and  isomaltose,  according  to 
Emmerling. 

The  yeast  enzymes  may  be  grouped  as  follows: 

1.  Hydrolysing  enzymes: 

a.  Sugar  splitting: 

Invertase,   Maltase,  Lactase,    Melibiase,  Raffinase,  Tre- 
halase,  Diastase  and  a  glycogen-splitting  enzyme. 

b.  Proteolytic. — Endotryptase. 

c.  Coagulating. — Rennet. 

2.  Oxidising:     Oxydase,  Catalase. 

3.  Reducing  enzymes. 

4.  Fermenting  enzymes:  zymase. 

Invertase  splits  sucrose  into  dextrose  and  lasvulose;  raffmose  is 
broken  up  into  laevuose  and  melibiose  (Bau).  Invertase  was  first  iso- 
lated by  Berthelot.  It  occurs  in  brewery  and  other  culture  yeasts  as 
well  as  in  most  wild  yeasts,  is  easily  soluble  in  water,  thereby  differ- 
ing from  other  sugar-splitting  enzymes,  acts  only  in  acid  solution  and 
is  not  affected  by  drying  for  one  hour  at  140  to  150°. 

Maltase  changes  maltose  into  dextrose;  is  difficultly  soluble  in  water 
and  can  only  be  extracted  from  crushed  and  ground  cells  by  leaching; 
it  occurs  in  most  yeast  types;  optimum  temperature  (Lindner  and 
Kroeber),  40°.  It  is  destroyed,  according  to  Beyerinck,  at  50  to  55°. 

Melibiase. — This  splits  melibiose  into  dextrose  and  galactose;  it  is 
soluble  in  water  and  has  been  extracted  from  bottom  fermenting  yeasts 
by  leaching  dried  cells  with  water.  It  occurs  also  in  some  of  the  top 
fermenting  yeast  types  (Lindner). 


212  YEAST. 

Raffinase  splits  raffinose,  but  not  sucrose.  It  occurs  in  several 
yeasts. 

Lactase  splits  lactose  into  d-galactose  and  dextrose  and  occurs  in 
only  a  few  saccharomycetes,  never  in  brewery  culture  yeast.  It  has 
been  found  in  Kefir  organisms;  it  does  not  diffuse  or  penetrate  the  cell 
wall. 

Trehalase,  splits  trehalose,  not  diffusing.  E.  Fischer  proved  its 
presence  in  the  Frohberg  type,  and  considers  it  identical  with  diastase ; 
Effront  does  not  agree  with  this  view. 

Glycogen-splitting  Enzyme. — This  was  found  in  the  yeast  juice 
obtained  by  E.  Buchner  under  high  pressure.  It  ferments  glycogen 
which  is  not  accomplished  by  the  yeast  proper.  It  probably  plays 
an  important  part  in  the  "so-called"  self-fermentation  or  auto -digestion. 
Wroblewski  considers  it  identical  with  diastase. 

Diastase. — Starch  is  also  attacked  (Wroblewski)  by  yeast  juice  in  a 
small  degree,  while  the  yeast  proper  has  no  action  upon  the  same. 
Lately  yeasts  have  been  discovered  capable  of  fermenting  dextrins. 

Proteolytic  Enzyme. — The  presence  of  this  enzyme  was  proved 
by  Will,  Wehmer,  and  Beyerinck.  Beyerinck  considers  it  similar  to 
trypsin,  as  proteolysis  is  stronger  in  alkaline  than  in  acid  gelatin. 
Hahn,  however,  claims  it  must  act  in  an  acid  solution;  its  optimum 
action  occurs  in  0.2%  solution  of  hydrochloric  acid  (similar  to  pepsin). 
Yeast  juice  proteins  lose  their  power  of  coagulation  after  10  to  14 
days'  auto-digestion.  The  products  are  tyrosin,  leucin,  xanthin  bodies, 
passive  albumoses,  but  no  peptones. 

Hahn  and  Geret  have  established  the  following  properties  of  yeast- 
endotryptase;  it  is  precipitated  from  yeast  juice  by  alcohol;  cannot  be 
separated  from  invertase;  gives  no  reaction  with  Millon's  reagent. 
Optimum  temperature,  40  to  45°,  destroyed  at  60°;  retains  its  effi- 
ciency in  yeast  juice  9  to  15  days  at  37°.  Endotryptase  plays  an  im- 
portant role  in  the  auto-digestion,  or  self-fermentation  of  the  yeast. 

Coagulating  Enzymes. — The  presence  of  a  coagulating  enzyme 
in  yeast  juice  was  proved  by  Rapp  and  in  extracts  obtained  by  treat- 
ing yeast  with  chloroform  under  pressure  at  60°.  It  coagulates  boiled 
milk,  acts  towards  alkalies,  acids  and  salts  as  rennet,  and  is  destroyed 
in  solution  by  heating  for  two  hours  at  65°;  very  resistant  when  dry, 
remains  efficient  in  juice  for  months;  does  not  dialyse. 

Oxidising  Ferments. — Effront  first  presumed  the  presence  of 
such  an  enzyme  in  yeast,  as  heat  is  generated  when  air  is  passed 


CARBOHYDRATES    OF    YEAST.  213 

through  finely-ground  yeasts  and  yeast  juice.  Gruess  established 
its  oxidizing  action  upon  tetramethyl-i-4-diamidobenzene  (violet); 
alcohol  weakens  it;  heat  (60  to  65°.)  destroys  its  action. 

According  to  Loew's  investigations,  there  also  exists  in  yeast  the 
enzyme  called  catalase,  which  he  claims  to  be  capable  of  decomposing 
hydrogen  peroxide  with  the  formation  of  oxygen. 

The  presence  of  reducing  enzymes  is  indicated  in  yeast  juice  by  the 
generation  of  nitrogen  from  nitrites,  of  hydrogen  sulphide  from  sulphur 
and  thiosulphates,  as  well  as  the  reduction  of  iodine  to  hydriodic  acid. 
The  optimum  temperature  is  40°.  The  reduction  of  methylene  blue 
is  especially  of  an  enzymic  character. 

Fermenting  Enzyme. — E.  Buchner  first  showed  (1897)  the  existence 
of  an  enzyme  capable  of  splitting  sugar  into  alcohol  and  carbonic- 
acid  gas,  and  gave  it  the  name  "Zymase." 

Zymase  is  contained,  in  addition  to  the  other  enzymes  mentioned, 
in  the  juice  obtained  by  means  of  hydraulic  pressure  from  the  yeast 
previously  ground  in  mixture  with  quartz  and  infusorial  earth;  the 
zymase  can  also  be  extracted  by  water  or  glycerol  from  yeast  that  is 
previously  killed  with  ether  or  acetone  and  then  finely  ground.  Bot- 
tom yeasts  are  generally  more  suitable  for  the  production  of  zymase. 

The  yeast  juice  ferments:  dextrose,  fructose,  maltose,  sucrose 
quickly,  raffinose  slowly,  glycogen  and  starch  very  slowly,  galactose 
very  little.  Lactose,  arabinose  and  mannose  are  not  fermented. 

The  zymase  does  not  dialyse  and  its  active  power  is  destroyed  in  the 
juice  at  40  to  50°;  it  acts  much  more  slowly  than  other  enzymes;  it 
is  precipitated  by  alcohol  and  ether  together  with  other  substances. 
It  may  be  evaporated  to  dryness  at  low  temperature  without  materially 
injuring  its  efficiency;  the  residue  may  be  heated  to  85°  for  8  hours 
without  harm;  it  may  be  preserved  for  i  year  without  losing  its  fer- 
mentative energy.  Its  deterioration  in  the  juice  is  due  to  the  presence 
of  endotryptase. 

The  action  of  zymase  is  increased  by  weak  alkalies,  such  as  potassium 
carbonate  or  sodium  hydrogen  phosphate.  A  temperature  of  28  to  30° 
causes  the  quickest  action,  but  the  highest  fermenting  power  is  attained 
at  12  to  14°.  In  30  to  40%  sugar  solutions  zymase  produces  the 
largest  percentage  of  carbon  dioxide,  but  the  speed  of  fermentation 
is  highest  in  10  to  15%  solutions.  Thirty  to  40%  sugar  solutions 
generate  0.8  grm.  of  carbon  dioxide  within  96  hours.  The  yeast  juice 
retains  its  fermentative  power  even  in  a  dilution  of  1.25. 


214  YEAST. 

Antiseptics  do  not  materially  influence  the  action  of  zymase;  it  may 
be  preserved  without  injury  by  toluene,  chloroform,  sugar  and  glycerol. 
The  proportions  of  carbon  dioxide  and  alcohol  produced  by  fer- 
mentation are  approximately  equal;  succinic  acid  and  glycerol  are 
apparently  not  formed.  Up  to  the  present,  zymase  has  never  been 
obtained  in  the  pure  state;  a  preparation  of  active  fermentative  power 
may  be  made,  according  to  Buchner,  Albert,  and  Rapp,  from  "  pre- 
served yeast,"  ("Dauerhefe")  made  by  bringing  yeast  into  ether  or 
acetone  or  by  heating  yeast  in  a  stream  of  hydrogen.  Such  yeast 
finely  ground  with  sand  can  be  used  for  the  production  of  powerful 
fermentative  agents.  The  percentage  of  zymase  in  yeast  varies;  it 
increases  if  the  yeast  is  stored  at  low  temperatures. 

Variation  of  Saccharomycetes. — The  practical  application  of 
Hansen's  pure  culture  system  is  based  upon  the  assumption  that  pure 
culture  yeast  does  not  suffer  any  physical  changes  in  practice.  At 
times  changes  have  been  observed  in  such  yeasts,  which  were  only  tem- 
porary, but  Hansen  succeeded  in  cultivating  varieties  and  types  with 
permanent  characteristic  properties. 

The  Circulation  of  Yeast  in  Nature. — The  normal  source  and 
origin  of  yeast  are  the  damaged  surfaces  of  sweet  juicy  friuts,  the 
juice  of  which  forms  the  natural  and  best  nutrient  for  their  propaga- 
tion. Rain  washes  the  yeasts  to  the  ground,  where  they  remain  during 
winter  and  spring,  whence  they  are  again  transferred  to  their  summer 
breeding  places.  Insects  are  active  factors  of  transferring  and  dis- 
tributing the  yeast  cells.  Soils  of  orchards  are  especially  rich  in  yeasts. 

Important  Yeast  Types  of  the  Brewing,  Distilling  and  Wine 
Industries. — Culture  yeasts  are  such  that  have  been  cultivated  for  long 
years  in  the  fermentation  industries,  possessing  certain  qualities  which 
make  them  especially  adapted  and  available. 

CULTURE  YEASTS. 

The  following  are  those  most  frequently  mentioned  in  literature: 

1.  Saccharomyces   Cerevisia. — Hansen,  from  English    and  Scotch 
breweries;  a  vigorous  beer  top  yeast. 

2.  Carlsberg  Bottom  Yeast,  i. — Hansen. 

3.  Carlsberg  Bottom  Yeast,  2. — Hansen. 

No.  i  produces  very  stable  beer,  not  so  readily  clarifying. 
No.  2  beers  not  so  stable,  but  with  better  clarification. 


CULTURE    YEAST.  215 

4.  Four  Culture  Yeasts  from  Munich  Station  (described  by  Will). 
Tribes  93,  2,  6  and  7;  the  first  two  having  a  high  fermenting 
power,  tribe  6  with  a  medium,  and  tribe  7  with  a  low  fermen- 
ting power. 

5.  Distillery    Yeast,    II,    Berlin,    isolated    from  .  a   distillery   in 
West  Prussia,    is   a   top   yeast  of  the  Frohberg  type,  suited 
for    fermenting     highly    concentrated    mashes,    difficult    to 
ferment  and   possessing    great    power   of   resistance  to  high 
alcoholic  content. 

6.  Berlin   Race,   V,  mostly  used    for    the  manufacture  of  com- 
pressed yeast. 

7 .  Wild  Yeast. — Saccharomyces  Pastorianus,  /,  II,  III. — Hansen. 
Sausage-shaped    cells,  disease   ferments    in   beer.     I  imparts 
a   bitter  taste   and  odor;  III   causes   turbidity.     I  may  give 
a  good  product  in  the  preparation  of  wine.     All  occur  in  air. 
II  and  III  are  top  yeasts,  I  is  a  bottom  yeast. 

8 .  Saccharomyces  ellipsoideus,  I  and  II. — Hansen. 

Yeast  I. — A  wine  yeast,  found  by  Hansen  on  the  surface  of  ripe 
grapes  in  the  Vosges  district,  cells  have  an  ellipsoidal  shape; 
found  to  be  useful  and  active  in  wine  fermentation. 
Yeast  II  is  a  dangerous  disease  yeast  for  breweries  causing 
turbidity.     Two  similar  types  have  been  isolated  by  Will. 

9 .  Saccharomyces  ilicis  (bottom  yeast)  and  S.  aquifolii  Gronlund 
(top  yeast)  found  on  fruit  of  Ilex  aquifolium.     They  produce 
bitter  and  disagreeable  taste  in  worts;  cells  mostly  spherical  in 
shape. 

10 .  Saccharomyces  pyriformis — Marshall  Ward.    Produces  alcoholic 
fermentation   of   English    ginger   beer,    forms   together   with 
Bacterium  veriforme  the  so-called  gingerbeer  plant,  used  for 
the  production  of  an  acid  frothing  beverage— ginger  beer. 

1 1 .  Saccharomyces  membranafaciens. — Hansen.  Found  in  wines,  also 
in  polluted  waters;  generates  from  sugar  no  alcohol,  but  acids; 
propagates  in  the  presence  of  12  %  alcohol;  consumes  maltic, 
acetic  and  succinic  acids ;  destroys  the  bouquet  of  wine. 

12 .  Saccharomyces  mali,  Du  Clauxi,  Kayser,  isolated  from  cider;  fer- 
ments invert  sugar,  and  produces  esters  (bouquet). 

13.  Schizoaccharomyces  pombe,  found  by  Saare  in  pombe   (negro 
millet  beer)  from  Africa     A  top  yeast,  fermenting  also  dextrin ; 
used  in  South  American  distilleries  with  success. 


2l6  YEAST. 

14.  Schizosaccharomyces     mellacei.  —  Jorgensen.      Isolated     from 
Jamaica  rum.     Greg  claims  to  have  found  8  similar  species  in 
Jamaica  rum  mashes. 

15 .  Schizosaccharomyces  octosporus. — Beyerinck.  Found  on  currants 
and  raisins  (Greece);  ferments  maltose  and  dextrose,  but  not 
saccharose,  shows  characteristic  ascus  formation. 

PURE  CULTURE  OF  YEAST  AND  ITS  APPLICATION 
IN  PRACTICE. 

Pasteur  showed,  that  bacteria  could  cause  disease  and  detrimental 
effects  in  these  industries,  and  that  one  of  the  principal  sources  of  in- 
fection in  the  brewery  was  the  open  coolship.  His  proposal  to  replace 
the  coolship  by  closed  apparatus  was  not  universally  approved  and 
did  not  find  any  practical  recognition.  The  reason  is  that  this  method 
does  not  prevent  beer  diseases,  as  another  and  very  dangerous 
source  of  infection  still  exists,  namely,  the  employment  of  impure 
yeast. 

Pasteur  had  advocated  a  cleaning  of  yeast  by  means  of  tartaric  acid, 
which  kills  part  of  the  bacteria,  but  he  at  that  time  did  not  know  the 
existence  of  the  abnormal  or  disease  yeasts  and,  as  Hansen  proved 
later,  the  addition  of  tartaric  acid  favored  the  development  of  these 
disease  yeasts. 

Hansen  proved  in  1879  that  numerous  abnormal  phenomena  were 
directly  caused  by  yeasts  which  are  contained  in  the  pitching  yeast 
besides  culture  yeasts.  He  showed  that  the  culture  yeast  does  not 
consist  of  a  uniform  species,  but  of  many  varieties,  of  which  each  one 
imparts  to  beer  peculiar  properties  and  which  employed  collectively 
may  at  times  even  cause  disease  phenomena.  Actuated  by  these  in- 
vestigations, Hansen  founded  his  system  of  the  use  of  pure  culture 
yeasts  in  breweries,  based  upon  the  fact  that  by  systematic  selection 
a  single  suitable  type  may  be  made  from  the  culture  yeast  which  is 
alone  allowed  to  develop  in  the  wort. 

The  pure  cultivation  of  yeast  is  made  by  the  following  method : 
A  suitable  quality  of  yeast  is  mixed  with  sterile  water,  and  a  small 
quantity  of  this  mixture  is  distributed  into  wort  gelatin  so  that  the 
various  cells  are  separated  from  each  other  on  cover-glasses.  These 
cover-glasses  are  then  transferred  to  small  moist  chambers  and  the 
development  of  one  cell  is  continually  observed  under  the  microscope. 


PURE    CULTURE    OF    YEAST.  217 

After  these  colonies  are  large  enough  a  part  of  them  is  carefully  trans- 
ferred into  sterile  wort  for  further  propagation.  In  this  manner  an 
absolutely  pure  culture  is  obtained  from  a  single  cell;  these  cells  are 
examined  as  to  their  action  in  wort  and  the  most  suitable  or  appro- 
priate species  are  selected  for  use  in  practice.  Hansen  showed  that 
the  properties  of  the  yeasts  in  practice  are  not  subject  to  variation  in 
a  serious  degree,  and  that  some  varieties  quickly  assume  their  old 
characteristics. 

The  so-procured  culture  yeast  is  then  transferred  to  larger  quantities 
of  a  nutrient  wort,  and  in  a  short  time  sufficient  yeast  is  propagated 
for  a  large  quantity  of  wort.  The  time  and  period  of  stability  and 
purity  of  such  a  cultivated  yeast  differs  according  to  general  con- 
ditions, seasons,  etc.,  and  the  resisting  powers  of  the  different  pure 
culture  species  differ  considerably. 

It  is,  therefore,  required,  to  introduce  new  pure-culture  yeast  periodic- 
ally into  a  brewery;  as  soon  as  the  biological  tests  and  control  show  any 
deterioration  of  the  pitching  yeast,  it  should  be  renewed.  The  pro- 
duction of  large  quantities  of  pure  cultivated  yeast  is  accomplished 
in  the  so-called  pure-culture  apparatus  in  breweries  and  institutes 
devoted  to  fermentation  industry  in  the  manner  described  by 
Hansen. 

The  apparatus  provides  for  aeration  of  the  sterilised  wort  with  filtered 
air;  the  wort  is  continually  fermented  and  the  yeast  sediment  is  re- 
tained. Hansen  introduced  personally  the  production  and  application 
of  pure-culture  yeast  in  bottom  fermenting  breweries,  and  the  largest 
plants  in  the  world  work  according  to  his  system,  which  has  abolished 
all  empiricism  and  replaced  it  by  absolutely  safe  working  methods  in 
practice.  The  pure  culture  of  top  fermenting  yeast  was  first  applied 
in  practice  by  Jorgensen  in  1885. 

Spirit  and  Compressed  Yeast. — The  pure-culture  system  has 
also  found  recognition  by  these  industries  owing  to  the  efforts  of  Prof. 
Lindner  in  Berlin.  He  has  introduced  Race  II  for  almost  all  dis- 
tilleries in  Germany  with  good  results.  In  the  United  States  they  are 
only  used  to  a  limited  extent. 

Recently,  pure  cultures  of  lactic  acid  have  been  used  together  with 
pure-culture  yeast  in  the  distilling  industry  in  order  to  prevent  the 
harmful  butyric  acid  fermentation.  The  pure  culture  has  also  been 
used  for  the  manufacture  of  compressed  yeast,  particularly  by  the 
efforts  of  Lindner  who  recommended  Race  V  for  this  industrv. 


2l8  YEAST. 

PURE    CULTURE  IN  WINE    INDUSTRY. 

This  has  been  introduced  especially  since  Wortmann  has  proved 
by  his  searching  investigations  that  different  wine-yeast  types  are 
capable  of  yielding  most  different  products  in  regard  to  acidity, 
bouquet,  as  well  as  taste.  It  was  also  expected  that  yeasts  from 
different  localities  would  impart  to  any  must  some  characteristics, 
but  it  is  found  that  the  taste  and  bouquet  are  dependent  to  a  much 
larger  degree  upon  the  type  of  grapes,  the  soil,  degree  of  ripeness, 
and  some  other  factors.  The  bouquet  substance  and  flavor  of  yeast  are 
of  a  volatile  nature;  the  use  of  foreign  wine-yeast  types  has,  therefore, 
been  abandoned,  and  pure  cultures  are  mostly  made  from  the  yeast 
types  found  on  the  native  grapes  and  in  the  produced  wines. 

The  main  advantage  of  pure  culture  in  wine  manufacture  is  the 
rapid  and  vigorous  fermentation  before  the  foreign  germs  and  wild 
yeasts,  especially  apiculatus  or  the  equally  dangerous  acetic-acid  bac- 
teria, are  capable  of  any  vigorous  development.  Pure-culture  wines 
also  clarify  quicker  and  better,  and  the  bouquet  of  the  young  wines  is 
generally  purer. 

Owing  to  the  extremely  short  season  of  wine  fermentation  and  the 
great  variability  of  yeast  types  for  the  wine  manufacture,  the  pure  cul- 
tures are  not  cultivated  in  large  apparatus  as  in  the  brewing  industry, 
but  the  yeasts  are  fermented  in  small  quantities  by  establishments 
specially  devoted  to  this  work.  The  wine  producer  propagates  this 
yeast  in  about  2.5  to  3  gallons  (10  to  12  liters)  of  pure  boiled  must 
and  adds  this  to  the  bulk  of  his  must  as  soon  as  it  is  in  a  vigorous  stage 
of  fermentation. 

Very  good  results  have  been  obtained  in  the  manufacture  of  spark- 
ling wines  by  Wortmann,  who  isolated  races  having  the  characteristic 
property  of  forming  a  solid  sediment  on  the  cork  and  producing  but 
very  little  turbidity. 

Seifert  has  introduced  the  pure  culture  especially  for  production  of 
sweet  wines,  which  are  distinguished  by  their  resistance  towards  high 
concentration  of  sugar  and  alcohol. 

CIDER    MANUFACTURE. 

In  the  production  of  this  beverage  pure  cultures  have  already  been 
introduced  successfully  by  Wortmann,  and  Kramer.  Jorgensen, 
Kayser  and  Nathan  have  investigated  their  use  in  this  field  and  rec- 


YEAST    IN    BAKING.  219 

ommend  the  same  procedure  as  in  the  wine  manufacture.  The  re- 
sults have  been  satisfactory,  the  yeasts  imparting  to  the  cider  a  more  or 
less  vinous  taste  and  flavour. 


YEAST    IN    BAKING. 

Saccharomyces  cerevisicz  generates  in  the  dough  carbon  dioxide 
and  alcohol  from  the  dextrose  and  maltose  formed  in  bread  during  the 
raising  and  baking  process.  The  alcohol  assists  the  carbon  dioxide  in 
its  raising  power  of  the  dough,  causing  the  sponginess  of  bread,  owing 
to  the  fact  that  it  is  mostly  volatilised  in  baking.  Top  fermenting 
yeast  was  mostly  used  formerly;  the  bottom  fermenting  yeast  is  very 
slow  in  action  and  bitter;  both  kinds  of  yeast  have  now  been  entirely 
replaced  by  the  so-called  " compressed  yeast." 

The  yeast  mash  forms  an  abundant  yeast  foam  which  is  skimmed 
off,  washed,  watered  and  deprived  of  most  of  its  water  by  filter  presses 
or  centrifuges. 

Air  yeast  is  produced  from  yeast  mash  in  large  fermenting  vats  by 
aerating  it  with  sterilised  air.  After  a  fermentation  of  20  hours,  the 
yeast  is  washed  and  pressed  in  filter  presses. 

Good  compressed  yeast  is  of  a  light,  pale  yellow  color,  somewhat 
crumbly,  not  slimy,  and  of  a  pleasant  odour.  It  must  be  protected 
from  light  and  air,  and  kept  at  low  temperatures;  it  should  be  even  in 
texture,  should  have  no  sourness,  an  apple  or  fruity,  not  cheesy 
odour,  and  should  not  exhibit  any  dark  specks  and  streaks.  It  is  some- 
times mixed  with  starch,  but  this  is  not  necessary,  as  the  machinery  of 
to-day  removes  the  water  sufficiently.  The  former  occasional  addi- 
tion of  gypsum  and  chalk  as  adulteration  is  hardly  met  with  to-day. 

At  times  bottom  yeast  from  which  the  bitter  taste  has  been  removed 
is  added  to  compressed  yeast;  this  may  be  recognised  by  the  absence 
of  spore  colonies  and  the  remnants  of  organic  hop  particles,  especially 
the  lupulin  or  oil  glands  of  hops. 

Authorities  seem  to  differ  in  regard  to  the  addition  of  starch,  but 
most  of  them  state  that  starch  is  added  for  the  purpose  of  reducing 
cost,  and  consider  it  a  reduction  of  quality  and  a  distinct  adulteration. 
The  addition  of  starch  should  be  stated  on  the  label. 

Compressed  yeast  should  be  used  when  fresh ;  it  easily  becomes  stale 
and  deteriorates;  it  is  generally  wrapped  in  tinfoil  and  kept  cold; 
texture  and  fracture  should  be  uniform  and  even. 


220  YEAST. 

Dry  yeast  is  classed  by  Leach  as  a  product  obtained  by  mixing 
fresh  yeast  with  starch  or  meal  into  a  stiff  dough  which  is  subsequently 
dried  at  low  temperature  and  under  reduced.pressure;  this  preparation 
is  said  to  keep  for  a  long  time,  and  although  the  cells  are  largely  ren- 
dered inactive  by  the  drying  process,  they  do  not  lose  their  power  of 
fermentation. 

PHYSICAL  EXAMINATION  OF  YEAST. 

Examination  of  the  physical  charactertistics  of  yeast  is  often  made 
by  the  chemist,  and  is  no  doubt  of  some  practical  value,  although 
the  results  cannot  be  claimed  as  decisive.  Among  the  more  important 
physical  tests  the  following  may  be  mentioned: 

1.  The  yeast  should  form  a  solid  sediment  after  fermentation. 

2 .  The  yeast  should  be  crumbly,  not  doughy  or  slimy. 

3.  Odour  should  be  pleasant,  pure,  clean,  aromatic,  not  sharp, 
repulsive,  or  cheesy,  taste  slightly  and  agreeably  bitter. 

4 .  Colour  should  be  light  yellow  (sometimes  darker  from  beers  with 
deeper  colour. 

5 .  Mixed  with  cold  water  it  should  settle  rapidly  and  form  a  solid 
compact  sediment. 

For  a  more  extensive  and  comprehensive  examination  we  must 
resort  to  a  microscopical  and  biological  examination. 

MICROSCOPICAL    EXAMINATION. 

Some  of  the  sample  is  mixed  with  sterilised  water  to  a  milky  fluid, 
some  of  this  is  brought  by  means  of  a  sterile  glass  rod  upon  a  slide, 
the  cover-glass  put  on  and  the  yeast  examined  with  a  power  of  600  to 
.800.  Thus  the  form,  shape  and  size  of  the  cells  are  observed,  the  con- 
dition of  the  cell  membrane  and  the  cell  contents  (protoplasm) ;  the 
presence  of  dead  yeast  cells  is  determined  by  adding  to  another 
sample  of  the  water  and  yeast  mixture  a  drop  of  stain,  such  as 
methyl  violet,  eosin,  or  fuchsin.  A  solution  of  the  stain  is  made  by 
dissolving  i  grm.  of  the  dye  in  160  c.c.  of  water  and  i  c.c.  of  alcohol. 
Living  and  active  cells  do  not  absorb  the  stain  so  readily,  while  dead 
cells  are  immediately  stained. 

Lindner  recommends  the  following  stain  and  method:  i  part  of 
powdered  indigo  is  rubbed  with  4  parts  of  concentrated  sulphuric 


221 

acid,  allowed  to  stand  24  hours,  diluted  with  20  to  30  times  its  volume 
of  water,  heated  to  50°  and  neutralised  with  calcium  or  sodium 
carbonate.  To  a  sample  of  yeast  i  drop  of  staining  solution  is  added, 
allowed  to  act  a  few  seconds,  diluted  with  a  weak  sucrose  solution, 
the  whole  thoroughly  mixed  and  a  drop  examined  on  the  slide  under  a 
cover-glass.  Old  and  dead  yeast  cells  exhibit  a  thickened  membrane.- 
A  good  yeast  should  contain  no  more  than  3  to  4  %  of  stained  cells. 

The  microscope  field  shows  also  the  presence  of  foreign  ferments r 
the  addition  of  other  substances,  such  as  starch,  as  well  as  con- 
tamination with  mould  spores  and  bacteria.  The  detection  of  the 
latter  is  simplified  by  adding  a  5  %  sodium  hydroxide  solution  to  the 
preparation. 

It  is  obvious  that  a  yeast  should  be  as  free  as  possible  from  any 
contaminating,  foreign  organisms,  such  as  lactic,  acetic,  and  butyric 
acid  bacteria.  It  should  also  be  free  from  any  so-called  wild  or 
abnormal  yeasts  (as  described  below) .  These  are  generally  recognized 
by  their  variation  and  distinct  difference  in  shape,  although  the  presence 
of  abnormal  yeasts  (not  culture  yeasts)  should  always  be  corroborated 
by  the  so-called  plate  cultures  and  spore  methods  as  described  in 
special  works  by  Hansen  and  Klocker. 

The  formation  of  ascospores  as  studied  by  Hansen  proceeds  under 
the  following  prevailing  conditions: 

1.  Abundant  air  must  be  admitted  to  the  yeast  cells;  propagation 
occurs  on  a  moist  surface  (gypsum  block). 

2 .  Only  young,  vigorous  cells  produce  these  spores. 

3 .  The  optimum  temperature  is  25°  for  the  most  known  species. 

4 .  Some  few  species  form  spores,  even  if  present  in  fermenting,  nu- 
trient solutions. 

The  fundamental  differences  between  the  varous  species  are  espe- 
cially the  temperature  and  the  time  necessary  for  spore  formation^ 
/.  e.,  S.  cerevisia  is  distinguished  from  the  wild  yeasts  in  that  the 
latter  form  ascospores  in  a  much  shorter  time  under  the  same  conditions 
and  temperature.  The  ascospores  of  the  culture  yeast  are  also- 
much  larger  than  those  of  wild  yeasts. 

CHEMICAL    TESTING    OF   YEAST. 

The  water  and  ash  of  a  yeast  are  determined  according  to  the  stand- 
ard methods  of  food  analysis. 


222  YEAST. 

The  general  and  most  important  criterion  for  the  valuation  of  yeast 
in  the  fermentation  industry  is  the  so-called  fermentative  and  raising 
power  which  is  especially  required  for  the  valuation  of  compressed 
yeast. 

By  activity  or  energy  of  fermentation  is  understood  the  degree  of  in- 
tensity with  which  a  yeast  is  able  to  decompose  a  certain  quantity  of 
sugar  within  a  specified  time.  It  not  only  serves  to  distinguish  the 
various  yeast  species  from  each  other,  but  is  also  useful  in  establish- 
ing a  criterion  for  the  different  physiological  conditions  of  any  given 
species  of  yeast. 

The  methods  used  for  this  determination  are  based  upon  the  estima- 
tion of  the  carbon  dioxide  generated  from  a  sugar  solution.  The 
amount  is  ascertained  either  by  weight  or  by  volume.  The  former 
method,  according  to  Meissl,  is  especially  applicable  if  only  small 
amounts  of  yeast  are  at  disposal.  The  latter  (Hayduck  and  Kusserow) 
is  principally  used  to  examine  yeasts  in  practice. 

Meissl's  Method. — This  method  determines  the  weight  of  carbon 
dioxide  which  is  generated  by  i  grm.  of  yeast  within  6  hours  at  30° 
from  a  solution  in  ordinary  tap  water  of  a  mixture  of  400  grm.  of 
pure  sucrose,  25  grm.  of  ammonium  phosphate  and  25  grm.  of  potas- 
sium phosphate. 

According  to  Meissl,  a  "normal"  or  " standard"  yeast  is  one  that 
liberates  under  these  conditions  1.75  grm.  of  carbon  dioxide,  and 
the  energy  of  the  yeast  is  then  figured  as  100. 

.The  fermenting  power  is  then  found  according  to  the  following 
equation: 

1.75    :  n   =    100   :  x  in  which 

n   =   quantity  of  carbon  dioxide. 

Prior  found  according  to  this  method  the  following  values  for  the 
various  species: 

Carlsberg  bottom  yeast,  No.  i,  136 . 40 
Carlsberg  bottom  yeast,  No.  2,  106 . 13 
S.  pastorianus  I,  155.48 

II,  280.72 

III,  202.20 

S.  ellipsoideus,    I,  285 . 76 

II,  219.03 


FERMENTING    POWER.  223 

FERMENTING   POWER. 

Meissl's  Method. — Of  the  above  mixture  4.5  grm.  are  dissolved 
in  50  c.c.  of  tap  water;  it  is  also  suggested  to  use  gypsum  water  by 
mixing  15  parts  of  a  saturated  solution  of  calcium  sulphate  with  35 
parts  of  distilled,  aerated  water. 

The  solution  is  introduced  into  an  Erlenmeyer  flask  of  about  100  c.c. 
capacity,  together  with  exactly  i  grm.  of  yeast,  which  should  be  thor- 
oughly distributed  so  as  to  form  a  uniform  mixture  without  lumps. 
The  flask  is  then  fitted  with  a  doubly  perforated  rubber  stopper,  having 
2  tubes,  one  of  which  is  bent  and  passes  nearly  to  the  bottom  of  the  flask 
and  fitted  at  the  other  end  with  a  rubber  tube  and  glass  plug,  while  the 
other  is  connected  with  a  calcium  chloride  tube.  The  whole  ap- 
paratus thus  arranged  is  weighed  accurately  and  kept  in  a  thermostat 
or  water-bath  at  30°  for  6  hours.  At  the  end  of  this  time  it  is  removed 
from  the  thermostat,  quickly  cooled  in  cold  water,  the  rubber  tube  and 
glass  plug  taken  off  and  the  remaining  carbon  dioxide  drawn  out  by 
suction;  the  glass  plug  and  rubber  tube  are  replaced  and  the  flask 
carefully  weighed  as  before.  The  loss  of  weight  is  equal  to  the 
quantity  of  carbon  dioxide  generated  by  the  fermentation  of  the 
sugar  owing  to  the  activity  of  the  yeast.  A  good  compressed  yeast 
should  have  at  least  75  to  80  %  of  fermentative  energy  or  fermenting 
power. 

Methods  of  Hayduck  and  Kusserow. — In  both  methods  the 
carbon  dioxide  generated  by  a  given  quantity  of  yeast  in  a  certain 
sugar  solution  is  measured  by  volume.  Hayduck  measures  the  volume 
of  carbon  dioxide  directly,  while  Kusserow  ascertains  the  quantity  of 
water  displaced  by  it  and  measured  in  a  graduated  cylinder,  which 
serves  as  a  receptacle. 

Hayduck  uses  an  apparatus  similar  to  Scheibler's  carbon  dioxide 
apparatus  consisting  essentially  of  a  500  c.c.  burette  divided  into 
c.c.  and  connected  by  a  rubber  tube  with  a  large  glass  bulb. 

For  both  methods  the  following  procedure  is  prescribed:  40  grm.  of 
pure  sucrose  are  dissolved  in  400  c.c.  of  water  and  this  solution  brought 
to  30°.  10  grm.  of  compressed  yeast  are  intimately  mixed  with  successive 
portions  of  the  solution  in  a  porcelain  dish  until  no  more  lumps  are  visible. 
The  mixture  is  introduced  into  a  1000  c.c.  flask  and  the  porcelain  dish 
is  thoroughly  rinsed  with  the  remainder  of  the  sugar  solution  until  all  of 
the  solution  is  put  into  the  flask;  the  whole  is  now  thoroughly  shaken 


224  YEAST. 

and  placed  into  a  water-bath  at  30°  allowed  to  stand  open  in  the  bath 
for  i  hour,  while  carbon  dioxide  freely  escapes. 

The  flask  is  then  connected  by  means  of  glass  and  rubber  tubing 
with  the  apparatus  filled  with  water  to  the  zero  mark.  In  order  to 
avoid  any  absorption  of  carbon  dioxide  by  the  water,  a  little  petroleum 
is  used  floating  in  a  very  thin  layer  upon  the  water. 

After  i  /  2 -hour  connection  the  vent  is  closed,  the  flow  of  carbon 
dioxide  is  shut  off  and  the  measured  volume  of  gas  is  read  off  in  the 
burette  after  the  water  in  the  burette  and  the  glass  bulb  are  brought 
to  an  equal  level.  The  c.c.  of  carbon  dioxide  may  express  directly 
the  fermenting  power  of  the  yeast;  or  the  weight  of  sucrose,  which  has 
been  decomposed  by  100  grm.  of  yeast,  may  be  calculated  by  multiply- 
ing the  found  figure  by  0.03841;  as  342  grm.  of  sucrose  will  give 
176  grm.  carbon  dioxide,  i  c.c.  of  which  weighs  0.001977  grm.  The 
weight  of  sucrose  necessary  for  the  production  of  i  c.c.  carbon  dioxide  = 

iff*  0.001977  =  0.003841. 

Kusserow's  Method. — In  this  method  exactly  the  same  quantities 
of  materials  are  used,  but  after  the  flask  has  been  standing  in  the  water- 
bath  at  30°  for  an  hour  it  is  connected  with  another  flask  of  exactly 
the  same  capacity  absolutely  full  of  water.  This  flask  has  a  doubly 
perforated  stopper  through  which  pass  two  glass  tubes,  both  bent  at 
right  angles,  going  to  the  bottom  of  the  flask,  and  bent  again  at  right 
angles  under  which  is  standing  a  graduated  cylinder  of  500  c.c. 

After  an  hour  the  gas  is  allowed  to  pass  into  the  second  flask; 
it  forces  the  water  out  and  this  is  collected  in  the  graduated  cylinder. 

A  good  baker's  yeast  should  have  according  to  this  method  a  ferment- 
ing power  of  250  c.c. 

Kusserow  also  estimated  the  fermenting  power  after  the  first  and 
second  half-hour;  during  the  first  period  a  good  yeast  should  give  50  c.c. 
and  in  the  second  half-hour  150  c.c.  of  carbon  dioxide. 

Acidity. — 5  to  6  grm.  of  yeast  are  mixed  with  distilled  water,  in- 
troduced into  a  flask  and  titrated  with  normal  sodium  hydroxide 
using  phenolphthalein  as  an  indicator.  The  acid  degree  is  expressed 
in  mg.  of  the  alkali  for  100  grm.  of  yeast  or  in  %  of  lactic  acid,  i  c.c. 
normal  alkali  =  0.09  grm.  lactic  acid. 

Starch. — The  addition  of  starch  to  yeast  before  pressing  has  long 
been  customary,  basing  its  use  upon  the  drying  qualities  of  starch. 


BIBLIOGRAPHY.  225 

The  best  grades  of  compressed  yeast  contain  about  5  %.,  some  as  high 
as  50  %.      The  larger  amounts  are  looked  upon  as  an  adulteration. 
Estimation  of  Starch. — See  under  starch. 

BIBLIOGRAPHY. 

Additional  data  and  special  information  may  be  gained  from  the  following  pub- 
lications which  have  been  freely  consulted  by  the  writer: 

Ahrens.     Das  Gdhrungs-problem. 

Brown,  A.  J.     Handbook  of  Scientific  Brewing. 

Buchner,  E.  H.,  and  M.  Hahn.     Die  Zymasegdhrung. 

Effront.    Les  Diastases. 

Green- Windisch.     Die  Enzyme. 

Hansen,  E.  Chr.     Practical  Studies  in  Fermentation. 

Jago.    Science  and  Art  of  Breadmaking. 

Jorgensen.     Micro-Organisms  of  Fermentation. 

Kloecker.     Fermentation  Organisms. 

Koenig.     Chemie  der  Nahrungs  und  Genussmittel. 

Koenig.     Unters.  landw.  und  gewerbl.  ivichtiger  Stoffe. 

Lafar.     Technical  Mycology. 

Lindner,  P.     Mikroskopische  Betriebskontrolle. 

Lintner,   C.    J.     Handbuch  d.   landw.   Gewerbe. 

Moritz  and  Morris.     Text-book  Science  of  Brewing. 

Mayer,  A.     Die  Gdhrungschemie. 

Maercker.     Handbuch  der  SpirUusfabrikation. 

Oppenheimer.     Die  Fermente. 

Prior.     Chemie  und  Physiologic  des  Maizes  und  Bieres. 

Sykes.     Principles   and   Practice  of  Brewing. 


VOL.  I— 15 


NEUTRAL  ALCOHOLIC  DERIVATIVES. 


BY  HENRY  LEFFMANN. 

The  neutral  derivatives  of  the  alcohols  include  a  number  of  impor- 
tant bodies,  of  which  chloroform,  chloral,  ether,  some  esters,  formal- 
dehyde and  acetaldehyde  are  prominent  examples. 

ETHER. 

Ethyl  Ether.    Ethyl  Oxide. 

When  used  as  a  name  " ether"  always  signifies  ethyl  ether.  When 
employed  generically  the  word  has  a  wider  signification. 

Ether  is  obtained  in  many  reactions,  but  usually  by  distilling  alcohol 
with  strong  sulphuric  acid,  hence  the  common  name  "sulphuric  ether" 
— a  name  that  belongs  to  ethyl  sulphate.  The  reaction  consists  in  the 
production  of  ethyl  hydrogen  sulphate  (sulphovinic  acid),  and  this 
at  a  higher  temperature  acts  on  a  second  molecule  of  alcohol  with 
formation  of  ether. 

Theoretically,  a  limited  quantity  of  sulphuric  acid  is  capable  of 
converting  a  large  quantity  of  alcohol.  Advantage  is  taken  of  this  in 
practice,  but  the  formation  of  secondary  products  ultimately  interferes. 
The  first  distillate  contains  several  impurities,  among  which  are  alco- 
hol, water,  sulphurous  and  acetic  acids  and  oil  of  wine.  By  addition 
of  water  much  of  the  alcohol  may  be  eliminated,  the  ether  forming  a 
layer  on  the  surface.  The  acids  and  water  may  be  removed  of  by 
agitation  with  potassium  carbonate,  and  the  ether  obtained  nearly 
pure  by  redistillation. 

Ether  is  a  highly  volatile,  colourless,  odourous  limpid  liquid,  of  pun- 
gent, sweetish  taste.  It  boils  at  35°  and  has  a  sp.  gr.,  according  to 
Mendelejeff,  of  0.7195  at  15°,  or  6.7364  at  o°.  It  solidifies  at  —129° 
to  a  white  crystalline  mass,  which  liquifies  at  —117.4°.  It  is  sparingly 
soluble  in  water,  less  so  in  glycerol ;  the  solutions  are  neutral  to  ordinary 
indicators.  With  alcohol,  chloroform,  benzene,  petroleum  spirit,  fixed 
and  volatile  oils,  it  is  miscible  in  all  proportions. 

227 


228 


NEUTRAL   ALCOHOLIC    DERIVATIVES. 


Ether  dissolves  resins,  fats;  many  alkaloids;  phosphorus,  bromine, 
and  iodine ;  ferric,  mercuric  and  auric  chlorides ;  and  mercuric  (but  not 
mercurous)  iodide.  In  the  air,  it  oxidises  very  slowly  to  acetic  acid. 
Both  the  liquid  and  vapor  burn  freely  with  a  white  flame. 

Commercial  Ether. — Commercial  ether  contains  water  (i  part  of 
water  dissolves  in  35  of  ether)  and  considerable  quantities  of  alcohol. 
"  Ether,"  British  Pharmacopoeia,  is  described  as  having  a  sp.  gr.  of 
0.735,  and  containing  not  less  than  92  %  by  volume  of  real  ether. 

"  Ether,"  United  States  Pharmacopoeia,  is  a  liquid  composed  of  about 
96%  by  weight  ethyl  oxide  and  about  4%  of  alcohol  containing  a 
little  water.  Sp.  gr.  — 0.716  to  0.717  at  25°. 

"When  20  c.c.  are  shaken  with  20  c.c.  of  water  previously  saturated 
with  ether,  the  upper  layer  upon  separation  should  measure  not  less 
than  19.2  c.c.  If  10  c.c.  of  ether  are  shaken  occasionally  during  one 
hour  with  i  c.c.  of  potassium  hydroxide  solution,  no  colour  should  be 
developed  in  either  liquid  (absence  of  aldehyde)." 

Water  or  alcohol  in  ether  tends  to  raise  the  b.  p.  and  increase  the 
sp.  gr.  of  the  liquid. 

Dr.  Squibb  found  the  following  sp.  gr.  for  mixtures  of  ether 
(0.71890)  with  alcohol  (0.82016)  (  =  90.94%  by  weight  of  absolute 
alcohol);  the  observations  being  taken  at  15.5°,  and  compared  with 
water  at  the  same  temperature  taken  as  unity : 


Percentage 
of  ether  by 
weight. 

Specific 
gravity. 

Percentage 
of    ether    by 
weight. 

Specific 
gravity. 

Percentage 
of     ether    by 
weight. 

Specific 
gravity. 

99 

0.72021 

89 

0.73298 

79 

o  .  74495 

98 

0.72152 

88 

0.73428 

78 

0.74612 

97 

0.72284 

87 

0-73547 

77 

0.74729 

96 

0.72416 

86 

0.73666 

76 

0.74846 

95 

0.72541 

85 

0.73785 

75 

0-74975 

94 

0.72666                 84 

0.73904 

74 

0.75104 

93 

0.72792                 83 

0.74022 

73 

o.75233 

92 

0.72918 

82 

0.74141 

72 

0.75362 

9i 

o.73043 

81 

0.74260 

7i 

0.75492 

9° 

0.73168                 80 

0.74378 

7o 

0.75623 

Absolute  ether  forms  a  clear  mixture  with  any  proportion  of  oil  of 
copaiba.  If  alcohol  or  water  is  present  an  emulsion  is  formed  when 
shaken  with  a  considerable  proportion  of  the  oil.  Anhydrous  ether 
also  forms  a  perfectly  clear  mixture  with  an  equal  bulk  of  carbon 


ETHER.  229 

disulphide,  but  if  the  smallest  quantity  of  water  is  present  the  mixture 
is  milky. 

Tannin  is  not  affected  by  anhydrous  ether,  but  it  deliquesces  to  a 
syrup  if  a  small  proportion  of  alcohol  or  water  is  present. 

The  most  delicate  test  for  alcohol  in  ether  is  that  of  Lieben,  depend- 
ing on  the  formation  of  iodoform.  The  method  is  described  on  page 
105.  Careful  purification  is  necessary  to  obtain  ether  which  will  not 
respond  to  this  test;  mere  keeping  in  presence  of  moisture  generates 
traces  of  alcohol  sufficient  to  produce  the  reaction. 

Several  chemists  have  pointed  out  that  rosaniline  acetate  is  insolu- 
ble in  pure  ether  or  chloroform,  but  imparts  more  or  less  colour  to  these 
when  alcohol  or  water  is  present. 

When  a  sample  is  well  agitated  with  dry  calcium  chloride  to  remove 
alcohol  and  water,  it  loses  the  power  of  dissolving  the  rosaniline  salt, 
becoming  tinged  very  faintly  when  shaken  with  it. 

To  utilize  this  fact  for  the  estimation  of  small  quantities  of  alcohol 
in  ether,  Allen  suggested  the  following  process.  A  minute  quantity  of 
powdered  rosaniline  acetate  is  placed  in  a  narrow  test-tube,  10  c.c.  of 
the  ether  added,  the  tube  corked,  and  the  whole  agitated.  If  the  ether 
is  anhydrous,  the  colouration  of  the  liquid  will  be  almost  inappreciable. 
If  the  colouration  is  considerable,  10  c.c.  of  ether  treated  with  calcium 
chloride  is  placed  in  another  tube  of  the  same  bore  as  the  first,  adding 
the  dye  as  before,  o.i  c.c.  of  alcohol  is  then  added  from  a  finely 
divided  burette,  and  the  mass  shaken.  If  this  quantity  of  alcohol  is 
insufficient  to  produce  a  colour  equal  to  that  of  the  sample,  further  addi- 
tions of  alcohol  must  be  made  until  the  liquids  have  the  same  depth 
of  colour.  The  tint  is  best  observed  by  holding  the  two  tubes  side  by  side 
in  front  of  a  window  and  looking  through  them  transversely.  The  use 
of  a  piece  of  wet  filter-paper  behind  them  facilitates  the  observation. 
It  is  well  to  permit  the  alcohol  to  drop  right  into  the  ether,  and  not 
allow  it  to  run  down  the  sides  of  the  tube,  as  in  the  latter  case  it  will 
dissolve  any  adherent  particles  of  dye,  forming  a  solution  which  will 
be  precipitated  on  mixing  with  the  ether.  It  is  also  not  advisable 
to  dilute  the  sample  with  pure  ether,  so  as  to  reduce  the  color 
to  that  of  a  standard  tint.  In  practice,  each  o.i  c.c.  of  alcohol  added 
from  the  burette  may  be  considered  as  indicating  i  %  of  impurity 
in  the  sample;  the  error  thus  introduced  is  insignificant  when  the  per- 
centage of  alcohol  is  small.  The  method  is  unsatisfactory  when  the 
alcohol  exceeds  5  %  of  the  sample,  owing  to  the  intensity  of  the  colour. 


230  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

The  results  are  within  0.25  %  of  the  truth.  Occasionally  the  tints  of 
the  two  liquids  are  not  readily  comparable,  but  on  placing  the  tubes 
for  a  few  minutes  in  cold  water,  this  difficulty  is  overcome.  It  has 
been  pointed  out  by  E.  R.  Squibb,  that  this  test  fails  to  detect  less  than 
0.2  %  alcohol,  but  allows  the  recognition  of  very  minute  traces  of  water. 

Ether  free  from  alcohol  is  soluble  in  eleven  times  its  measure  of 
water.  Agitation  with  water  extracts  any  alcohol  it  may  contain,  and 
thus  diminishes  the  volume  of  the  ether.  With  certain  precautions, 
this  method  may  be  used  in  connection  with  the  above  test.  The 
following  are  the  details  of  the  procedure  that  Allen  devised:  A 
small  quantity  of  rosaniline  acetate  is  placed  in  a  separator  which  is 
then  filled  with  water  and  a  small  proportion  of  ether,  and  the  whole 
agitated.  A  coloured  etherised  water  is  obtained,  in  which  ether  is 
quite  insoluble,  while  alcohol  readily  dissolves.  10  c.c.  of  the  etherised 
water  are  run  into  a  glass  tube  holding  about  25  c.c.,  and  having  divi- 
sions of  o.i  c.c.;  10  c.c.  of  the  sample  of  ether  are  next  added, the  tube 
corked,  and  the  whole  well  shaken.  On  the  ether  rising  to  the  surface, 
its  volume  can  be  easily  read  off.  Any  reduction  in  its  volume  is  due 
to- admixture  of  alcohol.  Each  o.i  c.c.  lost  represents  i  %  of  alco- 
hol. If  the  alcohol  does  not  exceed  20  %  the  ether  will  be  colourless, 
and  the  result  of  the  experiment  will  be  correct;  but  if  the  alcohol  is 
much  above  20  %  the  ether  will  be  coloured,  and  the  result  below 
the  truth.  The  absence  of  colour,  therefore,  in  the  ethereal  layer,  in- 
dicates the  accuracy  of  the  experiment.  If  the  ether  is  coloured,  an 
accurate  result  can  still  be  obtained  by  adding  5  c.c.  of  anhydrous 
ether,  and  again  agitating.  It  is  better,  however,  to  dilute  a  fresh  por- 
tion of  the  sample  with  an  equal  bulk  of  pure  ether,  and  use  the  diluted 
sample  instead  of  the  original.  By  proceeding  in  this  manner  the  pro- 
portion of  alcohol  in  mixtures  of  that  liquid  with  ether  can  be  ascer- 
tained within  i  or  2  %  with  great  facility.  The  process  has  been  verified 
up  to  60  %  of  alcohol. 

In  all  cases  the  proportion  of  alcohol  must  be  deduced  from  the 
reduction  in  the  volume  of  the  ether,  and  not  from  the  increase  in 
that  of  the  aqueous  liquid.  Care  must  be  taken  to  prevent  any  vola- 
tilisation of  the  ether. 

Some  of  the  objectionable  impurities  in  ether  may  be  detected  by 
allowing  a  small  amount  not  less  than  10  c.c.  to  evaporate  at  ordinary 
temperature  on  filter-paper  lying  in  a  flat  dish.  The  odour  of  the  last 
portion  should  be  examined. 


ESTERS — COMPOUND    ETHERS.  231 

Good  ether  gives  no  unpleasant  odour.  Allen  noted  samples  of  ether 
which  liberated  iodine  from  potassium  iodide,  an  action  which  he 
ascribed  to  the  presence  of  ethyl  nitrite. 

Methyl  Ether. — When  methyl  alcohol  is  heated  with  sulphuric  acid 
it  yields  methylic  ether,  which  is  a  gas  condensible  only  at  a  very  low 
temperature,  and  the  solution  of  which  in  ordinary  ether  possesses 
anaesthetic  properties.  Ether  prepared  from  methylated  spirit  is 
known  as  "  methylated  ether,"  but  this  should  not  be  used  in  medical 
work. 

Spirit  of  Ether,  British  Pharmacopoeia,  is  a  solution  of  about  28  parts 
of  ether  in  72  of  rectified  alcohol.  The  United  States  Pharmacopceia 
preparation  is  prepared  by  mixing  325  c.c.  of  official  ether  and  675  c.c. 
of  official  alcohol.  Compound  spirit  of  ether,  United  States  Pharma- 
copceia, is  made  by  substituting  25  c.c.  of  "ethereal  oil"  for  an 
equal  quantity  of  the  alcohol  in  the  simple  spirit,  otherwise  as  in  that 
substance. 

ESTERS— COMPOUND  ETHERS. 

This  term  is  applied  to  the  products  of  acids  on  alcohols  with  elimi- 
nation of  water.  They  are  analogous,  therefore,  to  the  ordinary  inor- 
ganic salts: 

Esters  can  be  produced  in  many  ways.  The  following  are  general 
methods: 

By  the  action  of  concentrated  acids  upon  anhydrous  or  concentrated 
alcohols. 

By  distilling  an  alcohol  with  strong  sulphuric  acid  and  a  salt  of  the 
acid  the  radicle  of  which  is  to  be  introduced. 

By  dissolving  an  acid  in  an  alcohol  and  passing  hydrochloric-acid 
gas  into  the  solution. 

By  reaction  between  the  iodide  of  the  radicle  and  the  silver  salt  of 
the  acid. 

The  esters  are  analogous  to  salts,  but  they  rarely  react  directly  with 
the  ordinary  tests  for  the  contained  radicles. 

As  a  class,  they  are  mostly  colourless,  volatile  liquids  slightly  soluble 
in  water,  but  miscible  in  all  proportions  with  alcohol  and  ether. 

The  fats,  fixed  oils  and  waxes  consist  largely  of  esters,  but  are  consid- 
ered in  a  separate  section  on  account  of  differing  much  in  physical 
characters  and  practical  applications  from  the  esters  here  described. 

A  method  of  assay  applicable  to  most  esters  is  "saponification,"  by 


232  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

which  is  meant  decomposition  by  means  of  sodium  hydroxide  or  potas- 
sium hydroxide.  By  this  action  an  alcohol  and  a  salt  of  the  acid  radicle 
present  is  formed.  High-pressure  steam  decomposes  many  esters  by 
simple  hydrolysis,  often  erroneously  termed  saponification.  The 
two  actions  are  shown  in  contrast  in  the  following  equations: 

The  saponifying  substance  is  usually  dissolved  in  alcohol  or  glycerol. 
The  latter  liquid,  suggested  by  Leffmann  and  Beam,  is  especially  ap- 
plicable to  the  saponification  of  the  complex  esters  contained  in  fats, 
fixed  oils  and  waxes  and  its  preparation  and  use  is  described  in  con- 
nection with  the  analysis  of  that  class  of  substances.  Aqueous  solu- 
tions are  very  slow  in  action  and  the  direct  action  of  high-pressure  steam 
is  suitable  only  to  operations  on  the  large  scale. 

Many  esters  are  hydrolyzed  at  ordinary  temperatures  by  some 
enzymes.  Such  an  enzyme  is  found  in  the  secretion  of  the  pancreas; 
another  very  active  one  in  the  castor  bean.  Practical  use  of  the  latter 
enzyme  has  been  made  in  the  decomposition  of  oils  on  the  large  scale. 

The  following  are  the  details  of  the  ordinary  process  of  saponification 
which  is  practically  identical  with  that  of  Koettstorfer  for  the  examina- 
tion of  fats : 

A  volume  of  50  c.c.  (measured  with  the  greatest  attainable  accuracy) 
of  a  solution  of  potassium  hydroxide  (about  60  grm.  in  1000  c.c.  of  alco- 
hol) is  introduced  into  a  strong  bottle  holding  about  100  c.c.  A  weighed 
quantity  of  the  ester  (from  4  to  6  grm.)  is  then  added  in  such  a  manner 
as  to  avoid  loss.  This  may  be  contained  in  a  small  glass  bulb,  or  a 
known  weight  dissolved  in  pure  alcohol  may  be  added.  The  bottle  is 
closed  with  an  india-rubber  stopper  firmly  secured  by  wire,  heated  to 
100°  for  half  an  hour,  allowed  to  cool,  opened,  a  few  drops  of  phenol- 
phthalein  solution  added,  and  the  liquid  at  once  titrated  with  normal 
acid.  A  blank  experiment  is  made  by  heating  50  c.c.  of  the  reagent 
alone  for  half  an  hour  and  titrating.  The  difference  between  the  acid 
required  in  the  blank  experiment,  and  that  in  which  the  ester  was 
present,  is  acid  corresponding  to  the  alkali  neutralised  by  the  ether. 
Each  cubic  centimetre  of  normal  acid  represents  0.0561  grm.  of  potas- 
sium hydroxide,  or,  in  other  words,  each  i  c.c.  of  difference  between  the 
measure  of  the  acid  originally  employed,  and  that  used  in  the  blank 
experiment  represents  one  equivalent  in  mg.  of  the  ester  present. 

As  an  example :  Suppose  that  45  c.c.  of  normal  acid  were  employed 
in  the  blank  experiment,  and  that  8  c.c.  were  required  after  saponifi- 
cation. The  difference  of  37  c.c.  represents  the  alkali  taken  for  the 


ESTERS — COMPOUND    ETHERS.  233 

decomposition  of  the  ester.  As  each  centimetre  of  this  contains  56.1 
mg.  or  one  equivalent  in  mg.  of  alkali,  it  follows  that  the  sample  con- 
tained a  number  of  mg.  equal  to  37  times  its  equivalent.  Supposing 
the  weight  of  ester  was  4.810  grm.,  then  its  equivalent  would  be 
4810/37  =  130.  Of  course,  the  equivalent  thus  found  is  identical 
with  the -molecular  weight,  1/2  or  1/3  of  the  same,  according  to  the 
constitution  of  the  ester. 

Conversely,  if  the  equivalent  of  the  ester  known  to  be  130,  the  weight 
of  it  present  in  the  quantity  of  the  sample  taken  will  be  130  X  37  = 
4.810  grm. 

This  method  often  furnishes  valuable  evidence  of  the  purity  of  the 
substances  examined.  An  elementary  analysis  would  scarcely  detect 
10%  of  ethyl  alcohol  in  ethyl  acetate,  or  of  amyl  alcohol  in  amyl  ace- 
tate, but  the  saponification  process  would  indicate  these  with  certainty. 

After  decomposing  the  ester  and  titrating  with  acid,  further  knowledge 
may  be  obtained  as  follows: 

The  free  alcohol  is  removed  by  distilling  or  evaporating  the  liquid 
after  rendering  it  slightly  alkaline.  The  residue  is  treated  with  an 
amount  of  sulphuric  acid  double  that  sufficient  neutralise  the  alkali 
originally  added  (i.e.,  to  produce  potassium  hydrogen  sulphate),  and 
the  liquid  is  distilled.  The  acid  of  the  esters  will  be  liberated,  and, 
if  volatile  without  decomposition,  will  pass  more  or  less  perfectly  into 
the  distillate,  where  it  may  be  further  examined.  It  is  obvious  that 
if  such  operation  is  to  be  applied  sulphuric  acid  should  be  used  in 
the  titration. 

This  method  may  be  employed  for  the  estimation  of  chloroform 
and  chloral  hydrate  when  n  alcoholic  solution. 

Each  c.c.  of  difference  in  the  amounts  of  normal  sulphuric  acid 
required  will  represent  0.0299  grm.  of  chloroform  or  0.0331  grm.  of 
chloral  hydrate. 

For  estimation  of  esters  in  spirits,  see  page  195. 

Many  fruits  owe  their  flavour  to  mixtures  of  esters,  principally  those 
containing  the  alcohol  radicles  of  the  methyl  series.  It  has  become  a 
common  practice  to  use  artificial  esters  for  imitating  such  flavours.  The 
complete  analysis  of  the  mixtures  sold  is  often  impossible  at  present, 
but  special  ingredients  may  be  detected.  The  following  table  shows 
some  of  the  constants  of  the  more  important  esters  of  the  series  men- 
tioned above.  For  important  salicylic  and  benzoic  esters,  see  Vol.  II, 
part  3,  of  this  work. 


234 


NEUTRAL   ALCOHOLIC    DERIVATIVES. 


The  data  in  this  table  were  compiled  from  several  sources,  princi- 
pally Fehling's  Handu'drterbuch  d.  Chemie;  Meyer  and  Jacobsen's 
Lehrb.  d.  org.  Chem.,  and  Landolt  and  Bernstein's  Tabellen.  In  many 
cases  the  numbers  must  be  considered  as  provisional,  as  the  purification 
of  these  esters  is  difficult;  moreover,  all  compounds  of  this  series  con- 
taining more  than  three  carbon  atoms  in  either  radicle,  present  iso- 
meric  forms,  which  in  the  higher  members  are  quite  numerous;  these 
forms  will  differ  in  b.  p.  and  sp.  gr.  The  table  will  serve,  however, 
to  show  some  of  the  general  characters.  A  few  esters  require  descrip- 
tion at  considerable  length. 


B.  p.;  under  standard  \    Sp.  gr.;  at  o°,  unless 
pressure, unless  other-  |  •    otherwise  noted, 
wise  stated. 


Methyl  formate 

--0 

o  04.0 

Methyl  acetate.           ... 

o  Qtc6 

Methyl  butyrate     

96°-!  02° 

o  020 

Methyl  chloride  
Methyl  bromide  
Methyl  iodide  

-23-7° 

4-5° 
45° 

0.952 

!-732 
2  .  2QT. 

Methyl  sulphate  

i87°-i88 

I  .  327 

Ethyl  formate  

54-3° 

0.941; 

Ethyl  acetate  

74.6° 

0.8981 

Ethyl  butyrate 

II5°-I2I° 

o  004. 

Ethyl  nitrate 

87° 

i  109  at  20° 

Ethyl  nitrite 

17° 

o  900  at  15.15° 

Ethyl  sulphate            

06°  (i^  mm  ) 

i  184  at  19° 

Ethyl  chloride  
Ethyl  bromide  
Ethyl  iodide  
Isoamyl  formate  
Isoamyl  acetate 

12.2° 
38.4° 
72.3° 

116° 

148° 

0.925  (°°/°°) 
1.473  (°°/°°) 

I  .935    at  20°/20° 

0.874  at  21° 
o  8063 

Isoamyl  butyrate  

176° 

0.852  at  15° 

Isoamvl  nitrate  

I470-i48° 

0.999  ai  20° 

Isoamyl  nitrite 

Q4°-Qi;0 

O    QO2 

Isoamyl  chloride 

101° 

o  813 

Isoamyl  bromide 

121° 

1  .  236 

Isoamyl  iodide  

148° 

1.468 

These  constants  are  of  less  practical  value  than  is  usual  with  such 
data,  as  most  esters  are  encountered  in  commerce  in  more  or  less  com- 
plex mixture,  so  that  determinations  of  b.  p.  and  sp.  gr.  have  little 
indicative  value.  The  following  examples  of  formulas  for  commercial 
artificial  flavours  are  taken  from  a  recent  publication.  The  propor- 


ESTERS — COMPOUND    ETHERS.  235 

tions  are  parts  by  volume  added  to  100  parts  of  cologne  spirit  (see 
page  112). 

Pineapple  Flavor. — Chloroform,  i  part;  aldehyde,  i  part;  ethyl 
butyrate,  5  parts;  amyl  butyrate,  10  parts. 

Strawberry  Flavor. — Ethyl  nitrite,  acetate  and  formate,  each  i 
part;  ethyl  butyrate,  5  parts;  amyl  butyrate,  2  parts;  amyl  acetate, 
5  parts. 

Raspberry  Flavor. — Ethyl  nitrite,  acetate,  formate,  butyrate,  ben- 
zoate,  cenanthylate  and  sebacate;  methyl  salicylate;  amyl  acetate  and 
butyrate,  aldehyde:  each  i  part. 

In  the  examination  of  these  mixtures,  chloroform  and  allied  bodies 
can  be  detected  and  estimated  by  conversion  into  hydrochloric  acid, 
as  described  on  page  275,  aldehyde  by  the  methods  on  pages  197  and 
265;  nitrite  can  be  detected  even  in  minute  amounts  by  Greiss'  test 
(page  241)  and  if  present  in  notable  quantity  can  be  estimated  by  the 
standard  method  of  assay  (page  245). 

The  fruit  esters  are  usually  saponified  by  the  method  given  on  page  232 
As  many  of  them  are  highly  volatile,  the  operation  must  be  conducted 
in  a  flask  connected  closely  to  a  well-cooled  reverse  condenser.  A 
freshly-prepared  solution  of  pure  sodium  hydroxide  in  alcohol  as  free 
as  possible  from  esters  and  aldehyde  may  be  used.  Small  amounts 
of  methyl  alcohol  may  be  expected,  as  methyl  salicylate  is  often  present. 
Alcohol  is,  of  course,  to  be  avoided  as  the  solvent  for  the  saponifying 
agent,  when  it  is  desired  to  detect  or  estimate  ethyl  as  one  of  the 
radicles  present.  Water  or  glycerol  may  be  substituted  in  such  cases. 
The  saponification  with  water  is  usually  slow;  a  strong  solution  should 
be  employed  and  the  mixture  heated  for  some  time  either  in  a  strong, 
tightly-closed  flask  or  under  a  reverse  condenser.  In  all  cases  the  con- 
denser should  be  well  cooled.  The  glycerol  solution  is  made  by  mixing 
20  c.c.  of  a  50%  solution  of  sodium  hydroxide  with  180  c.c.  of  good 
glycerol. 

The  sodium  salts  resulting  from  the  saponification  may  be  sepa- 
rated by  distilling  the  mass,  care  being  taken  not  to  overheat  it, 
which  would  develop  empyreumatic  substances  that  interfere  seriously 
with  subsequent  tests.  The  distillate  contains  the  alcohols  produced 
by  the  saponification,  and  the  volatile,  unsaponifiable  ingredients, 
such  as  chloroform  and  aldehyde.  By  adding  sulphuric  or  phosphoric 
acid  in  slight  excess  to  the  solid  residue  and  again  distilling,  especially 
in  a  current  of  steam,  some  of  the  acids  may  be  obtained  in  the  distillate 


236  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

and  may  be  recognised  by  odour  and  special  tests.  It  is  often  impos- 
sible to  distil  all  the  acids  present  in  this  way. 

A  general  method  of  examining  esters  was  devised  by  Chapman  and 
Smith  (Jour.  Chem.  Soc.,  1871,  19,  477).  It  is  based  on  the  fact  that 
organic  bodies  when  oxidised  in  a  sealed  tube  by  a  mixture  of  sulphu- 
ric acid  and  potassium  dichromate  yield  proximate  products  of  oxida- 
tion closely  related  to  the  radicles  contained  in  them. 

The  process  consists  in  heating  a  known  weight  of  the  substance 
in  a  sealed  tube  for  some  hours  with  an  aqueous  solution,  containing 
from  3  to  8  %  of  potassium  dichromate  and  5  parts  by  weight  of 
concentrated  sulphuric  acid  to  every  4  of  the  dichromate.  The  fol- 
lowing reactions  were  verified  by  the  authors  of  the  method  as  occurring 
almost  in  theoretic  proportion. 

Ethyl  alcohol,       C2H6H  +  O2  =  HC2H3O2  +  H2O. 

Amyl  alcohol,       C5HI2O  +  O2  =  HCSH9O2  +  H2O. 

Ethyl  acetate,       C2HS,C2H3O2 +O2     =2HC2H3O2. 

Amyl  acetate,       C5HXI,C,HJ6,+Oj   =  HC2H3O2+HC5H9O2. 

Amyl  valerate,      CsHn^HpC^  +  Oa   =  2HC5H9O2. 

Amyl  nitrite,         C5HII,NO2+O3         =  HCSH9O2+HNO3. 

Ethyl  nitrate,        C2HS,NO3  +  O2          =  HC2H3O2  +  HNO3. 

Ethyl  iodide,        2C2HSI  +  Os  =  2HC2H3O2  +  H2O  + 12. 

Isopropyl  iodide,  2C3H7I  +  On  =2HC2H3O2  +  2CO,  +3H2O  +  I2. 

Ethylamine,          C2HS,H2N  +  O2  =HC2H5O2 +NH3. 

Ethylamylamine,  C2HS,CSHII,HN  +  O4  =  HC2H3O2  +  HC5H9O2  +NH3. 

Ethyl  benzoate,    C2HS,C7H5O2  +O2     =HC2H3O2 +HC7H5O2. 

Compounds  containing  methyl  yield  formic  acid  by  oxidation,  but 
the  greater  part  of  this  is  further  oxidised  to  carbon  dioxide  and  water. 
Chapman  and  Smith  (Jour.  Chem.Soc.,  1872,  20,  173)  further  showed 
that  the  process  was  capable  of  being  used  for  investigating  the 
structure  of  isomeric  bodies.  This  is  exemplified  in  the  equation 
representing  the  oxidation  of  isopropyl  iodide. 

These  methods  of  examining  esters  are  of  such  general  application 
that,  with  the  aid  of  the  table  on  page  234,  some  esters  in  common 
use  may  be  readily  identified,  and  even  quantitatively  assayed.  The 
assay  of  commercial  esters  may  usually  be  conducted  as  described 
under  " Ethyl  Acetate"  A  few,  however,  owing  to  their  special  prop- 
erties or  great  individual  importance,  will  be  considered  in  separate 
sections. 

Ethyl  Acetate  (Acetic  Ether).— This  is  prepared  by  distilling  dried 


ESTERS — COMPOUND    ETHERS.  237 

sodium  acetate  with  alcohol  and  sulphuric  acid.  The  product  is 
purified  from  alcohol  by  agitation  with  a  saturated  solution  of  calcium 
chloride,  and  subsequently  dehydrated  by  contact  for  some  days  at 
the  ordinary  temperature  with  recently  ignited  potassium  carbonate,  or 
distillation  over  dried  sodium  acetate.  The  use  of  solid  calcium  chlo- 
ride for  dehydration  causes  considerable  loss  from  the  formation  of 
a  compound  with  the  ethyl  acetate,  decomposed  on  addition  of  water. 

Ethyl  acetate  occurs  in  many  wines  and  in  wine  vinegar.  It  is  pro- 
duced spontaneously  in  several  pharmaceutical  preparations,  notably 
in  a  solution  of  ferric  acetate  in  alcohol.  It  possesses  considerable 
solvent  powers,  and  is  employed  for  extracting  morphine  and  tannins 
from  aqueous  liquids. 

It  is  a  colourless,  fragrant  liquid  having  a  sp.  gr.  of  about  0.908  at  15°, 
and  boils  at  73.5  to  74.3°.  It  is  miscible  in  all  proportions  with  alcohol, 
ether  and  chloroform,  but  only  sparingly  soluble  in  water,  requiring 
8  volumes  at  o°,  or  9  at  15°  for  its  solution.  The  solubility  of  water 
in  ethyl  acetate  is  i  measure  in  26  at  o°,  and  i  in  24  at  15°.  In  a  saturated 
solution  of  calcium  chloride,  ethyl  acetate  is  but  very  slightly  soluble, 
requiring  47  measures  at  15°,  and  almost  as  large  a  proportion  at  o°. 

Commercial  ethyl  acetate  is  often  impure.  In  a  series  of  eight  samples 
representing  the  products  of  most  of  the  leading  makers,  W.  Inglis 
Clark  found  proportions  of  real  ethyl  acetate  ranging  from  90.14 
to  30.6%;  the  alcohol  from  7.2  to  48.0%;  the  free  acetic  acid  from  a 
trace  up  to  7.0%;  while  the  other  impurities  (estimated  by  difference) 
ranged  from  1.5  to  29.6%. 

For  the  analysis  of  the  commercial  product  the  following  process 
gives  satisfactory  results: 

Dissolve  5  c.c.  in  proof  spirit  (freed  from  acid  by  adding  a  few  drops 
of  phenolphthalein,  and  then  dropping  in  dilute  alkali  until  a  faint  pink 
tint  remains  after  shaking)  and  titrate  with  decinormal  alkali.  Each 
i  c.c.  neutralised  represents  0.006  grm.  of  free  acetic  acid  in  the  5  c.c. 
used. 

Add  to  another  quantity  of  5  c.c.  of  the  sample  the  measure  of  alkali 
that  has  been  employed  in  the  titration,  and  then  saponify  the  neutral- 
ised liquid  as  described  on  page  232.  Each  i  c.c.  of  normal  alkali 
neutralised  by  the  sample  represents  0.088  grm.  of  ethyl  acetate  in  the 
quantity  of  the  sample  used,  or  0.046  of  alcohol  regenerated  from  the 
ester. 

20  c.c.  of  the  sample  are  mixed  with  20  c.c.  of  water  and  about  12  grm. 


238  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

of  solid  sodium  hydroxide  and  placed  in  a  flask  with  inverted  condenser. 
After  macerating  for  about  an  hour  at  room  temperature  the  mass  is 
heated  at  100°  for  two  hours,  then  20  c.c.  of  water  added  and  the  mix- 
ture distilled  until  50  c.c.  are  collected.  The  alcohol  distillate  is  esti- 
mated in  the  usual  way.  The  weight  so  found  is  divided  by  4  and  from 
the  dividend  is  substracted  the  amount  of  alcohol  produced  from  the 
ethyl  acetate  ascertained  by  the  Kottstorfer  method  on  page  232. 
The  difference  is  the  alcohol  present  as  such  in  5  c.c.  of  the 
sample. 

By  subtracting  the  sum  of  the  acetic  acid,  ethyl  acetate  and  alcohol 
found  as  above  from  the  weight  of  5  c.c.  of  the  sample,  the  total 
amount  of  other  impurities  may  be  ascertained. 

A  very  simple  and  approximately  accurate  method  of  ascertaining 
the  proportion  of  real  ethyl  acetate  present  consists  in  agitating  10  c.c. 
of  the  sample,  in  a  graduated  tube,  with  an  equal  volume  of  a  satu- 
rated solution  of  calcium  chloride.  The  volume  of  the  layer  which 
rises  to  the  surface  is  the  quantity  of  ethyl  acetate.  The  results  are 
fairly  accurate,  if  the  water  and  alcohol  of  the  sample  do  not  together 
much  exceed  20%  by  vo  ume,  but  with  larger  proportions  the 
volume  that  separates  is  sometimes  notably  below  the  real  amount 
of  ethyl  acetate  present.  The  error  may  be  avoided  in  some  measure 
by  adding  to  the  sample  twice  its  volume  ethyl  acetate  that  has  been 
previously  treated  with  calcium  chloride  solution.  20  c.c.  of  the 
fortified  sample  should  then  be  shaken  with  20  c.c.  of  calcium  chlor- 
ide, when  the  diminution  in  the  volume  of  the  ethereal  layer  will 
represent  the  measure  of  impurities  in  20/3  =  6.67  c.c.  of  the  sample. 

This  method  is  due  to  W.  Inglis  Clark.  The  employment  of  water 
previously  saturated  with  washed  acetic  ether,  and  coloured  with  a 
rosaniline  salt  does  not  give  satisfactory  results. 

The  sp.  gr.  of  ethyl  acetate  is  not  a  satisfactory  indication  of  its 
purity,  as  it  dissolves  alcohol,  ether,  and  chloroform  in  all  proportions 
and  may  be  diluted  with  a  spirit  of  approximately  the  same  sp.  gr. 
as  the  pure  substance. 

It  should  not  contain  more  than  a  trace  of  free  acid,  and  should  be 
entirely  volatile  without  residue,  nor  be  blackened  by  strong  sulphuric 
acid. 

The  United  States  Pharmacopoeia  requirements  refer  to  "  acetic 
ether"  containing  about  90%  of  ethyl  acetate,  about  10%  of  ethyl 
alcohol  and  a  little  water.  Sp.  gr.,  0883  to  0.885  at  25°-  When 


ESTERS — COMPOUND    ETHERS.  239 

evaporated  spontaneously  from  clean  unsized  paper,  the  final  odour 
should  not  suggest  that  of  pineapple. 

25  c.c.  shaken  in  a  graduated  tube  with  an  equal  volume  of  water 
previously  saturated  with  pure  ethyl  acetate  and  the  liquids  allowed 
to  separate  should  give  an  upper  (ether)  layer  measuring  not  less  than 
22.5  c.c. 

A  small  portion  of  ethyl  acetate  poured  upon  strong  sulphuric  acid 
should  not  develop  a  dark  ring  at  the  point  of  contact  of  the  two  liquids. 

Ethyl  Sulphates. — The  ethyl  sulphates  (sulphovinates)  are  the 
salts  of  ethyl  hydrogen  sulphate  sometimes  called  ethyl  sulphuric  acid 
or  sulphovinic  acid. 

Ethyl  hydrogen  sulphate  (acid  ethyl  sulphate)  is  produced  by  the 
interaction  of  alcohol  and  strong  sulphuric  acid.  The  action  is 
aided  by  keeping  the  mixture  at  100°  for  24  hours.  The  less  water 
present,  the  more  change  occurs;  but  it  is  always  far  from  complete. 
If  the  temperature  be  raised  much  above  100°,  ordinary  ether  is 
produced,  and,  at  higher  temperatures  still,  ethylene  (ethene)  and 
other  products  appear. 

From  the  crude  acid,  barium  ethyl  sulphate  may  be  prepared  by  neu- 
tralising the  liquid  with  barium  carbonate,  filtering  off  barium  sulphate, 
and  evaporating  the  filtrate  to  crystallisation.  The  calcium  salt  may  be 
obtained  in  similar  manner,  and  the  lead  salt  by  employing  lead  mon- 
oxide instead  of  barium  carbonate. 

Sodium  Ethyl  Sulphate,  may  be  obtained  by  decomposing  one  of 
the  above  salts  with  sodium  carbonate,  or  by  adding  powdered  sodium 
carbonate  and  alcohol,  or  alcoholic  solution  of  sodium  hydroxide,  to 
the  crude  acid,  filtering  from  the  insoluble  sodium  sulphate  and 
evaporating  the  filtrate  to  crystallisation. 

Sodium  ethyl  sulphate  (sodium  sulphovinate)  is  a  white  crystalline 
salt  of  faint  ethereal  odour,  and  cooling,  sweetish,  somewhat  aromatic 
taste,  very  deliquescent,  soluble  in  0.7  parts  of  cold  water,  and  also 
soluble  in  alcohol,  with  which  it  is  capable  of  forming  a  crystalline 
compound.  It  is  insoluble  in  ether.  At  86°  it  melts  and  becomes 
anhydrous;  at  120°  it  decomposes,  evolving  alcohol  vapour,  and  leaving 
acid  sodium  sulphate.  It  also  decomposes  spontaneously  at  ordinary 
temperatures,  especially  when  in  solution,  with  formation  of  sodium 
sulphate.  The  presence  of  a  little  free  alkali  prevents  this  change. 
The  commercial  salt  is  liable  to  contain  barium,  calcium,  lead,  arsenic. 
sulphates  and  other  impurities.  It  is  not  unfrequently  contaminated 


240  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

with  foreign  organic  matter.  When  pure  it  does  not  char  on  ignition. 
It  has  been  adulterated  by  admixture  with  sodium  sulphate  and  has 
been  replaced  by  barium  acetate.  The  last  dangerous  substitution 
would  at  once  be  detected  by  adding  dilute  sulphuric  acid  to  the  aque- 
ous solution. 

The  characters  of  the  ethyl  sulphates  are  sufficiently  indicated  by 
the  above  description  of  the  sodium  salt.  They  are  soluble  in  water. 
When  heated  with  dilute  sulphuric  acid  they  evolve  alcohol,  and  with 
strong  sulphuric  acid,  ether.  With  sulphuric  acid  and  an  acetate  they 
give  a  fragrant  odour  of  acetic  ether.  The  same  result  is  obtained  by 
simply  heating  together  an  acetate  and  sulphovinate. 

Ethyl  Sulphuric  Acid,  may  be  obtained  in  a  state  of  purity  by 
decomposing  the  barium  salt  by  an  equivalent  amount  of  dilute  sul- 
phuric acid  or  a  solution  of  lead  ethyl  sulphate  by  hydrogen  sulphide. 
On  concentrating  the  filtered  liquid,  the  acid  is  obtained  as  a  limpid, 
oily,  very  sour,  unstable  liquid  of  1.31  sp.  gr.  It  is  miscible  with 
water  and  alcohol  in  all  proportions,  but  it  is  insoluble  in  ether. 

Ethyl  Dithiocarbonates :  Xanthates. 

The  xanthates  have  the  composition  of  esters,  but  possess  decided 
acid  properties. 

When  boiling  absolute  alcohol  is  saturated  with  pure  potassium 
hydroxide  and  carbon  disulphide  added  gradually  till  it  ceases  to  be 
dissolved,  or  the  liquid  becomes  neutral,  potassium  xanthate  is  formed. 
On  cooling,  the  xanthate  crystallises  in  slender  colourless  prisms, 
which  must  be  pressed  between  blotting-paper  and  dried  in  a  vacuum. 
It  is  readily  soluble  in  water  and  alcohol,  but  insoluble  in  ether.  On 
exposure  to  air  it  suffers  gradual  decomposition. 

On  adding  dilute  sulphuric  or  hydrochloric  acid  to  potassium  xan- 
thate, xanthic  acid  is  liberated  as  a  colourless,  heavy,  oily  liquid, 
of  peculiar  and  powerful  odor  and  astringent  bterit  taste.  It  is 
very  combustible.  Xanthic  acid  reddens  litmus,  and  ultimately  bleaches 
it.  At  a  very  slight  rise  of  temperature  it  undergoes  decomposition 
into  alcohol  and  carbon  disulphide.  Owing  to  this  property  the  xan- 
thates have  been  successfully  used  as  a  remedy  for  Phylloxera,  which 
attacks  the  vine,  and  has  been  used  against  other  noxious  insects. 
The  xanthate  is  mixed  with  earth,  either  alone  or  together  with  super- 
phosphate, when  it  gradually  undergoes  decomposition  with  formation 
of  carbon  disulphide.  Xanthic  acid  possesses  powerful  antiseptic  prop- 
perties.  Sodium  xanthate  is  employed  to  effect  the  reduction  of  ortho- 


ESTERS — COMPOUND    ETHERS.  241 

nitrophenylpropiolic  acid  to  indigo  blue.  When  warmed  with  nitric 
acid,  xanthic  acid'  and  xanthates  evolve  an  odour  suggesting  ethyl 
nitrite.  On  distillation,  the  xanthates  are  decomposed  with  formation 
of  carbon  dioxide,  carbon  disulphide  and  hydrogen  sulphide  and  a 
peculiar  sulphuretted  oil,  while  a  sulphide  and  free  carbon  remain. 

The  most  characteristic  reaction  of  xanthic  acid,  and  the  one  from 
which  it  derived  its  name,  is  that  with  copper.  On  adding  copper  sul- 
phate to  a  neutral  solution  of  a  xanthate  a  brownish  precipitate  of  cupric 
xanthate  is  first  formed,  which  quickly  changes  to  bright  yellow  flocks  of 
cuprous  xanthate.  This  substance  is  insoluble  in  water  and  in  dilute 
acids,  but  is  decomposed  by  strong  acids.  It  is  slightly  soluble  in  alcohol 
and  rather  more  so  in  carbon  disulphide.  It  is  not  sensibly  attacked  by 
hydrogen  sulphide,  but  is  instantly  decomposed  by  sodium  sulphide. 
The  formation  of  cuprous  xanthate  has  been  utilized  for  detecting  car- 
bon disulphide  in  illuminating  gas,  the  gas  being  passed  through  alco- 
holic solution  of  potassium  hydroxide,  the  excess  of  alkali  neutralised 
by  carbonic  or  tartaric  acid,  the  insoluble  salt  removed  by  filtration, 
and  the  liquid  treated  with  copper  sulphate. 

Xanthates  may  also  be  estimated  by  titration  with  a  standard  solu- 
tion of  iodine,  or  by  oxidation  with  permanganate,  and  precipitation  of 
the  resultant  sulphate  by  barium  chloride. 

Nitrous  Ethers. — Two  of  these  are  of  importance,  owing  to  their  use 
in  medicine.  Several  other  substances  having  formulas  apparently 
identical  with  the  derivatives  of  nitrous  acid  are,  in  reality,  derivatives 
of  nitric  acid.  Such  are  nitrobenzene  and  nitroethane.  The  true 
nitrous  ethers  (esters)  are  capable  of  saponification  (see  page  232) 
yielding  a  nitrite.  Very  minute  amounts  of  nitrite  can  be  detected 
by  Griess'  test,  which  consists  in  adding  to  the  liquid  to  be  tested 
a  solution  of  sulphanilic  acid,  then  a  solution  of  a-naphthylamine, 
each  dissolved  in  strong  acetic  acid.  A  nitrite  will  produce  a  red 
liquid.  Only  a  very  minute  amount  of  the  substance  to  be  tested 
should  be  used  and  the  solution  should  be  allowed  to  stand  for  five 
minutes.  It  must  be  borne  in  mind,  however,  that  nitrites  are  pres- 
ent in  the  air,  water  or  even  dust,  hence  error  from  these  sources  must 
be  excluded.  Commercial  spirit  of  nitrous  ether  gives  this  reaction 
without  saponification.  One  drop  of  the  spirit  in  50  c.c.  of  water  is 
easily  detected.  It  is  possible  that  a  slight  hydrolysis  occurs  by  which 
nitrous  acid  is  formed. 

Etyl  Nitrite.     Nitrous  Ether. — This  substance  has  been  known  in 
VOL.  I— 16 


242  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

an  impure  state  for  a  long  time.  It  may  be  obtained  by  passing  the  red 
vapours  of  nitrogen  trioxide  (evolved  by  acting  on  starch  by  nitric 
acid)  into  alcohol;  by  distilling  potassium  (or  sodium)  nitrite  with  al- 
cohol and  sulphuric  acid;  or  by  the  direct  action  of  nitric  acid  on 
alcohol.  In  the  last  case  the  nitric  acid  is  reduced  by  a  portion  of  the 
alcohol,  and  the  nitrous  acid  so  formed  acts  on  the  remainder  to  form 
ethyl  nitrite.  A  considerable  quantity  of  aldehyde  results  from  the 
oxidation  of  the  alcohol,  so  that  the  ether  obtained  by  this  process  is 
largely  contaminated.  This  reaction  may  be  avoided  in  great  measure 
by  adding  metallic  copper  to  the  contents  of  the  retort. 

Pure  ethyl  nitrite  is  a  nearly  colourless  liquid  of  fragrant  odour. 
It  is  soluble  in  all  proportions  in  alcohol,  but  requires  about  fifty  parts 
of  water  for  solution.  It  boils  at  18°,  and  has  a  sp.  gr.  of  0.947  at  15.5. 
It  is  liable  to  decompose  on  keeping,  especially  in  presence  of  water. 
It  gives  many  of  the  ordinary  reactions  of  the  nitrites.  Thus,  when 
mixed  with  a  little  dilute  sulphuric  acid,  and  poured  on  a  strong  aque- 
ous solution  of  ferrous  sulphate,  it  develops  a  dark  brown  ring;  when 
dissolved  in  alcohol  and  treated  with  a  few  drops  of  dilute  sulphuric  or 
acetic  acid,  it  liberates  iodine  from  potassium  iodide,  and  therefore  the 
mixture  becomes  blue  on  addition  of  starch. 

Spirit  of  Nitrous  Ether. — " Spirit  of  nitrous  ether"  (Spiritus 
tztheris  nitrosi)  is  the  present  official  name  of  a  preparation  consisting 
essentially  of  a  solution  of  impure  ethyl  nitrite  in  rectified  spirit.  Spirit 
of  nitrous  ether  is  the  modern  representative  of  the  old  "sweet  spirit 
of  nitre  "  (Spiritus  nitri  dulcis,  London  Pharmacopoeia,  1745),  which  was 
prepared  by  distilling  together  rectified  spirit  and  nitric  acid. 

The  characters  of  " spirit  of  nitrous  ether"  are  thus  described  in  the 
British  Pharmacopoeia  of  1867:  "Transparent  and  nearly  colourless, 
with  a  very  slight  tinge  of  yellow,  mobile,  inflammable,  of  a  peculiar 
penetrating  apple-like  odor,  and  sweetish,  cooling,  sharp  taste.  Sp.gr., 
0.845.  It  effervesces  feebly  or  not  at  all  when  shaken  with  a  little 
"bicarbonate  of  soda."  When  agitated  with  solution  of  sulphate 
of  iron  and  a  few  drops  of  sulphuric  acid,  it  becomes  a  deep  olive- 
brown  or  black.  If  it  be  agitated  with  twice  its  volume  of  saturated 
solution  of  calcium  chloride  in  a  closed  tube,  2  per  cent,  of  its  original 
volume  will  separate  in  the  form  of  nitrous  ether,  and  rise  to  the  surface 
of  the  mixture."  In  later  reprints  of  the  British  Pharmacopoeia  of  1867 
the  words  "an  ethereal  layer"  are  substituted  for  "nitrous  ether"  in 
the  last  sentence. 


ESTERS — COMPOUND    ETHERS.  243 

The  spirit  of  nitrous  ether  of  the  German  Pharmacopoeia  has  a  sp.  gr. 
of  0.840  to  0.850;  the  United  States  Pharmacopoeia  requirement  is 
0.823  at  25°,  and  is  described  as  containing  not  less  than  4  per  cent,  of 
ethyl  nitrite. 

Spirit  of  nitrous  ether  is  a  liquid  of  very  complex  composition. 
Besides  the  ethyl  nitrite,  alcohol,  and  water  which  may  be  regarded  as 
its  normal  constituents,  it  usually  contains  aldehyde,  and  probably 
paraldehyde  and  ethyl  acetate  and  nitrate.  After  keeping,  sensible 
quantities  of  free  nitrous  and  acetic  acids  are  developed,  and  other 
changes  occur.  In  addition  to  the  foregoing  constituents,  the  occurrence 
of  which  is  generally  admitted;  according  to  Eykman,  spirit  of  nitrous 
ether  is  also  liable  to  contain  ethyl  oxide  (ether) ;  ethyl  formate  and  oxal- 
ate;  cyanogen  compounds;  glyoxal;  glyoxalic,  oxalic,  malic,  and  sac- 
charic acids;  to  which  list  Allen  suggested  the  addition,  as  a  possible 
constituent,  of  nitroethane,  a  body  isomeric  with  ethyl  nitrite,  but  hav- 
ing a  sp.  gr.  of  1.058  and  boiling  at  m°  to  113°. 

The  tendency  of  spirit  of  nitrous  ether  and  similar  preparations  to 
undergo  gradual  deterioration  with  destruction  of  the  nitrous  ether  is 
a  point  of  importance.  The  exact  conditions  are  not  thoroughly  under- 
stood, but  it  is  established  that  excess  of  water  favors  the  destruction  of 
the  ester.  Hence  adulteration  of  sweet  spirit  of  nitre  with  water,  a 
common  practice,  not  only  dilutes  the  preparation,  but  greatly  enhances 
the  tendency  of  the  nitrous  ether  to  undergo  decomposition.  Allen 
found  that  a  sample  kept  perfectly  well  for  very  many  months  when 
diluted,  but  a  portion  of  the  same  mixed  with  one-third  its  volume  of 
water  contained  no  nitrous  ether  after  an  interval  of  4  months.  In 
these  experiments  the  samples  were  kept  in  well-closed  bottles.  Im- 
perfect closing  of  the  bottle,  exposure  to  light  or  to  excessive  tempera- 
ture, will  cause  loss  of  so  volatile  a  substance  as  this  ester.  On  the 
other  hand,  a  solution  of  the  pure  ester  in  nearly  absolute  alcohol 
was  kept  7  years  and  still  contained  ethyl  nitrite  and  mere  traces  of 
free  acid. 

Analysis  of  Spirit  of  Nitrous  Ether. — The  assay  of  spirit  of  nitrous 
ether  is  somewhat  difficult,  on  account  of  the  complex  character  of  the 
preparation.  The  sp.  gr.,  behaviour  with  sodium  acid  carbonate,  and 
reaction  with  ferrous  sulphate  in  presence  of  free  acid  are  serviceable; 
but  the  test  with  solution  of  calcium  chloride  is  worthless. 

The  following  methods  are  the  most  satisfactory  of  many  that  have 
been  devised: 


244  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

Excess  of  water  can  be  detected  by  the  sp.  gr.  of  the  sample.  The 
British  Pharmacopoeia  spirit  is  0.845  at  15.5°,  but  a  slightly  higher 
figure  may  be  tolerated.  If,  however,  it  exceeds  0.853,  excess  of  water 
is  indicated.  Commercial  samples  are  sometimes  adulterated  so 
largely  with  water  as  to  bring  the  sp.  gr.  to  0.910  or  even  higher; 
an  inferior  spirit  of  0.900  sp.  gr.  being  sold  wholesale.  A  sp.  gr. 
of  0.845  corresponds,  according  to  the  accepted  alcohol  tables  to  a 
content  of  81.36  %  by  weight  of  absolute  alcohol,  or  151.78  %  by 
volume  of  proof  spirit.  The  extent  to  which  a  sample  has  been  diluted 
with  water  may  be  found  by  multiplying  the  percentage  of  proof  spirit 
(as  found  by  the  table)  by  the  factor  65 7  (  =  TOT°.T*)»  when  the  product 
will  be  the  percentage  by  volume  of  spirit  of  nitrous  ether  of  standard 
contained  in  the  sample.  To  find  the  percentage  by  measure  of  spirit 
of  0.850  sp.  gr.  originally  present,  the  percentage  of  proof  spirit  in 
the  sample  should  be  multiplied  by  0.673  (  =  100/148.8). 

The  nitrous  ether,  though  of  higher  sp.  gr.  than  alcohol,  is  present  in 
too  small  proportion  to  affect  sensibly  the  estimation  of  water  from 
sp.  gr.  The  addition  of  water  to  sweet  spirit  of  nitre  is  reprehensible, 
for  it  reduces  the  immediate  strength  and  medicinal  value  of  the  prep- 
aration and  renders  it  more  liable  to  change. 

Free  acid  will  be  indicated  by  the  reaction  with  litmus  paper,  and 
by  the  effervescence  occasioned  on  adding  sodium  carbonate  to  the 
sample.  A  notable  proportion  of  free  acid  renders  the  spirit  incom- 
patible with  potassium  iodide,  from  which  it  liberates  iodine.  The 
proportion  of  acid  may  be  ascertained  by  titration  with  standard  alkali, 
but,  as  some  samples  contain  both  free  acetic  and  free  nitrous  acid,  it 
is  sometimes  of  interest  to  determine  them  separately,  which  is  done  by 
P.  MacEwan  in  the  following  manner:  10  c.c.  measure  of  the  sample 
is  placed  in  a  flask  containing  a  drop  of  phenolphthalein  solution,  and 
two  or  three  drops  of  methyl-orange  solution  are  next  added.  A  porce- 
lain slab,  spotted  with  drops  of  methyl-orange  solution,  is  arranged  in 
readiness.  N/2  solution  of  sodium  hydroxide  is  then  rapidly  added  to 
the  contents  of  the  flask,  and  as  soon  as  the  red  begins  to  fade,  a  drop 
of  the  liquid  is  removed  by  a  glass  rod  and  brought  in  contact  with 
a  spot  of  the  methyl-orange  on  the  plate.  If  the  spot  assumes  a 
pink  tint,  the  nitrous  acid  is  not  quite  neutralised,  in  which  case  the 
addition  of  the  alkali  solution  is  continued,  until,  on  retesting,  a  spot 
of  methyl-orange  is  rendered  only  faintly  pink.  The  volume  of 
standard  alkali  used  is  then  noted,  and  the  titration  continued  until 


ESTERS — COMPOUND   ETHERS.  245 

the  pink  tint  produced  by  the  phenolphthalein  denotes  alkalinity. 
Each  c.c.  of  the  alkali  first  used  represents  0.0235  grm.  of  nitrous 
acid,  while  each  c.c.  of  the  additional  alkali  requisite  to  produce  the 
phenolphthalein  reaction  corresponds  to  0.0300  grm.  of  acetic  acid. 
The  process  is  approximate  only. 

The  United  States  Pharmacopoeia  requires  that  "when  freshly  pre- 
pared, or  even  after  being  kept  for  some  time  "  the  spirit  of  nitrous 
ether  should  not  be  acid  to  litmus.  Even  when  quite  old  it  should 
not  effervesce  with  potassium  hydrogen  carbonate. 

Aldehyde  will  be  indicated  by  the  brown  produced  on  heating 
the  sample  with  potassium  hydroxide.  A  sample  free  from  an  exces- 
sive proportion  of  aldehyde,  when  treated  at  the  ordinary  temperature 
with  half  its  volume  of  a  dilute  solution  of  potassium  hydroxide,  assumes 
a  yellow  colour  which  gradually  deepens,  but  does  not  become  brown 
in  twelve  hours. 

The  United  States  Pharmacopoeia  test  for  presence  of  aldehyde  is : 

If  10  c.c.  of  the  spirit  are  mixed  with  10  c.c.  of  potassium  hydroxide 
of  3  %  strength,  the  mixture  will  assume  a  yellow  colour  which  should 
not  turn  decidedly  brown  within  twelve  hours. 

Ethyl  chloride  and  other  chlorinated  bodies  may  be  detected  by 
igniting  a  little  of  the  sample  in  a  porcelain  basin  and  holding  a  beaker 
moistened  with  silver  nitrate  solution  over  the  flame.  If  silver  chloride 
be  formed,  the  sample  may  be  evaporated  with  sodium  hydroxide  and 
the  chloride  in  the  residue  determined. 

Total  Ethyl  Nitrite.— The  following  is  a  summary  of  the  United 
States  Pharmacopoeia  process  for  ascertaining  the  amount  of  ethyl 
nitrite  in  spirit  of  nitrous  ether. 

Shake  30  grm.  of  the  sample  with  0.5  grm.  of  potassium  hydrogen 
carbonate,  transfer  the  liquid  to  a  tared  flask  marked  at  100  c.c.j 
weigh  accurately,  add  sufficient  alcohol  to  make  100  c.c.,  and  mix  well. 
Put  10  c.c.  of  this  mixture  into  a  nitrometer,  add  10  c.c.  of  potassium 
iodide  solution  (20  %)  and  100  c.c.  of  normal  sulphuric  acid.  Allow 
the  volume  of  evolved  gas  to  become  constant — which  will  require 
about  from  30  to  60  minutes — and  note  amount.  Multiply  this  by 
0.307  and  divide  by  the  weight  of  the  sample  taken.  At  the  standard 
temperature  used  in  the  United  States  Pharmacopoeia  (25°)  and  at  the 
usual  standard  pressure  (760  mm.)  the  quotient  will  be  the  percentage 
of  ethyl  nitrite  in  the  liquid.  To  correct  for  temperature  deduct  1/3 
of  i  %  for  each  degree  above  the  standard  temperature,  and  add  1/3 


246  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

of  i  %  for  each  degree  below  that  temperature.  To  correct  for  pres- 
sure add  4/30  for  each  mm.  above  the  standard  and  deduct  4/30  for 
each  mm.  below  the  standard. 

The  following  special  requirement  is  also  given  by  the  United  States 
Pharmacopoeia:  If  a  test-tube  is  half-filled  with  the  spirit  and  put  into 
a  water-bath  heated  to  65°  until  it  has  acquired  this  temperature,  the 
liquid  should  boil  distinctly  upon  the  addition  of  a  few  small  pieces  of 
broken  glass. 

Ethyl  Nitrite  may  be  detected  by  the  brown  produced  by  adding 
ferrous  sulphate  to  an  acidulated  solution  of  the  sample  of  spirit.  Of 
various  ways  of  making  the  test,  Allen  found  the  following  the 
best :  10  c.c.  of  the  spirit  is  mixed  with  5  c.c.  of  a  strong  aqueous  solu- 
tion of  ferrous  sulphate.  Pure,  concentrated  sulphuric  acid  should 
next  be  poured  down  the  side  of  the  test-tube  in  such  a  manner  as  to 
form  a  distinct  stratum  under  the  spirituous  mixture.  A  brown  zone 
will  thereupon  be  produced  at  the  junction  of  the  two  layers,  the  inten- 
sity of  which  is  an  indication  of  the  strength  of  the  sample  in  nitrous 
ether.  With  good  samples,  the  colouration  is  increased  and  extended 
by  causing  the  layers  to  become  partially  mixed,  but  with  inferior  speci- 
mens the  brown  colour  is  more  or  less  destroyed  by  such  treatment  (see 
also  page  241). 

Methylated  Spirit  is  said  to  be  occasionally  employed  for  the  prepara- 
tion of  sweet  spirit  of  nitre.  The  substitution  may  be  detected  by  agi- 
tating 30  c.c.  of  the  sample  with  3  or  4  grm.  of  ignited  potassium 
carbonate,  treating  15  c.c.  of  the  decanted  dehydrated  spirit  in  a  small 
flask  with  10  grm.  of  anhydrous  calcium  chloride,  attaching  a  con- 
denser, and  heating  the  flask  in  boiling  water  till  about  5  c.c.  has 
passed  over  or  scarcely  any  further  distillate  can  be  obtained.  The 
operation  proceeds  slowly,  but  requires  little  attention  and  should  be 
carried  out  thoroughly.  The  contents  of  the  flask  are  next  treated 
with  5  c.c.  of  water,  and  another  2  c.c.  distilled.  This  second  distil- 
late is  then  oxidised  by  potassium  dichromate  and  sulphuric  acid,  as 
described  on  page  236,  and  the  product  tested  with  silver  nitrate.  If 
the  sample  was  free  from  methyl  alcohol,  the  solution  darkens,  and 
often  assumes  transiently  a  purple  tinge,  but  continues  quite  translu- 
cent; and  the  test-tube,  after  being  rinsed  out  and  filled  with  water, 
appears  clean  or  nearly  so.  If  the  sample  contains  only  i% 
of  methylic  alcohol  (  =  10  to  20%  of  methylated  spirit),  the  liquid 
turns  first  brown,  then  almost  black  and  opaque,  and  a  film  of  silver, 


ESTERS — COMPOUND    ETHERS.  247 

which  is  brown  by  transmitted  light,  is  deposited  on  the  tube.  When 
the  sample  is  methylated  to  the  extent  of  3  or  4  %  the  film  is  suf- 
ciently  thick  to  form  a  brilliant  mirror.  The  observations  should 
be  made  by  daylight. 

Nitrates  may  be  detected  and  determined  by  applying  the  phenol- 
disulphonic  acid  method  (vol.  3,  part  3,  page  3,  foot-note  3).  The 
liquid  should  be  saponified  (see  page  232)  with  sodium  (or  potassium) 
hydroxide,  made  up  to  a  convenient  volume,  an  aliquot  part  evaporated 
on  the  water-bath  and  treated  with  the  reagent  as  directed  at  the 
reference  given  above. 

Concentrated  Spirit  of  Nitrous  Ether. — For  the  convenience  of 
pharmacists,  some  manufacturers  prepare  a  mixture  of  nitrous  ether  and 
alcohol  of  definite  strength,  so  that  by  adding  a  given  volume  to  a  given 
volume  of  alcohol,  a  liquid  of  official  strength  is  obtained.  A  Philadel- 
phia manufacturer  has  devised  a  plan  of  furnishing  this  concentrated 
form  in  sealed  tubes  of  amber  glass.  These  are  well-cooled,  the  point 
broken,  the  contents  promptly  mixed  with  a  pint  of  alcohol,  and  a  little 
more  than  a  pint  of  U.  S.  P.  %  spirit  of  nitrous  ether  obtained.  The 
concentrated  preparation  usually  contains  about  16%  of  alcohol 
and  82  %  of  ethyl  nitrite.  Under  ordinary  circumstances,  the  assay 
of  this  will  include  estimation  of  the  amount  of  ethyl  nitrite  and 
of  the  impurities  to  which  that  substance  is  liable.  The  simplest 
plan  seems  to  be  to  add  a  measured  volume  of  the  sample  to  a  known 
volume  of  pure  alcohol  and  examine  the  liquid  according  to  the  methods 
already  given  for  the  commercial  spirit. 

W.  A.  Pearson  (Amer.J.  Pharm.,  1908,  80, 101)  has  devised  aprocess 
for  ascertaining  the  amount  of  alcohol  in  the  concentrated  prep- 
aration. 

Ethyl    Chloride.     Hydrochloric    Ether.     " Sweet  Spirit  of    Salt." 

Ethyl  chloride  is  a  fragrant,  volatile  liquid,  boiling  at  12.2°,  and 
burning  when  ignited  with  a  smoky,  green-edged  flame,  producing 
fumes  of  hydrochloric  acid.  Sp.  gr.,  0.911  to  0.916  at  8°.  It  is  spar- 
ingly soluble  in  water,  but  readily  so  in  alcohol,  neither  solution  giving 
a  precipitate  with  silver  nitrate. 

Ethyl  chloride  is  used  as  an  anesthetic  and  is  now  sold  in 
sealed  glass  tubes  which  must  be  kept  in  a  cool  place.  When  the 
point  of  the  tube  is  broken  at  ordinary  temperatures,  the  liquid 
vapourizes  at  once,  producing  a  readily  inflammable  vapor,  much 
heavier  than  air. 


248  NEUTRAL  ALCOHOLIC    DERIVATIVES. 

The  United  States  Pharmacopoeia  gives  the  following  test  for  ethyl 
alcohol  which  may  be  present  in  the  commercial  chloride:  10  c.c. 
of  the  sample  are  agitated  with  10  c.c.  of  cold  water  and  the  super- 
natant layer  of  ethyl  chloride  allowed  to  evaporate  spontaneously.  A 
few  drops  of  dilute  sulphuric  acid  and  a  few  drops  of  potassium  dichro- 
mate  solution  are  then  added  and  the  mixture  boiled.  Alcohol  will 
be  indicated  by  an  odor  of  aldehyde  and  a  greenish  or  purplish  tint  in 
the  liquid. 

Ethyl  chloride,  evaporated  from  clean,  bibulous  paper,  should  leave 
no  unpleasant  odour. 

Ethylidene  Chloride,  Chlorinated  Ethyl  Chloride,  or  /?-Dichlor- 
ethane,  CH3.CHC12.  This  is  now  prepared  in  a  pure  state  by  the 
action  of  chlorine  on  ethyl  chloride,  or  by  distilling  aldehyde  with 
phosphorus  pentachloride.  Ethylidene  chloride  possesses  anaesthetic 
properties.  The  isomer,  ethylene  dichloride,  Dutch  liquid,  produces 
severe  convulsions  when  its  vapour  is  inhaled.  Ethylidene  chloride 
is  distinguished  by  not  reacting  with  potassium,  whereas  Dutch 
liquid  is  violently  acted  on,  forming  a  porous  mass  and  evolving  hy- 
drogen and  chlorethylene,  C2H3C1,  the  latter  being  a  gas  of  alliaceous 
odour.  The  same  gas  is  produced  when  Dutch  liquid  is  heated  with 
alcoholic  solution  of  potassium  hydroxide,  while  ethylidene  chloride 
is  unaffected.  The  b.  p.  and  sp.  gr.  also  distinguish  Dutch  liquid  from 
its  isomer.  From  chloroform,  ethylidene  chloride  is  distinguished  by 
its  sp.  gr.,  b.  p.,  and  negative  reaction  with  Hofmann's  test.  (See 
p.  274). 

Ethyl  Bromide.     Hydrobromic  ether. 

This  has  been  employed  in  medicine  as  an  anaesthetic.  It  boils  at 
38.4°,  and  has  a  sp.  gr.  of  1.473  at  °°-  It  burns  with  difficulty,  giving 
a  bright  green  but  smokeless  flame,  and  forming  fumes  of  hydro- 
bromic  acid.  The  b.  p.  and  smokeless  flame  distinguish  it  from  ethyl 
chloride. 

Ethyl  bromide  is  liable  to  contain  an  admixture  of  ethyl  ether, 
which  reduces  the  sp.  gr.,  Some  samples  are  contaminated  with  an 
acid  impurity  that  has  an  extremely  unpleasant  odour,  and  is  less  volatile 
than  ethyl  bromide.  Such  specimens  are  unfit  for  use.  For  general 
tests  see  under  Ethyl  Chloride. 

Ethyl  carbamate. 

Carbamic  acid  is  amidocarbonic  acid  It  can  be  obtained  by  the 
action  of  ethyl  alcohol  upon  urea.  It  forms  colourless,  odourless 


ESTERS — COMPOUND    ETHERS.  249 

crystals  having  a  sharp,  somewhat  cooling  taste.  It  is  soluble  in  less 
than  its  weight  of  water  and  alcohol,  in  about  an  equal  weight  of 
ether,  in  1.3  parts  of  chloroform  and  3  parts  of  glycerol.  These  pro- 
proportions  are  for  a  temperature  of  25°.  It  melts  between  47.5° 
and  50°  and  at  a  higher  temperature  it  is  decomposed,  burning 
without  leaving  an  appreciable  residue. 

The  following  tests  for  purity  are  condensed  from  the  United  States 
Pharmacopoeia.  Ethyl  carbamate  mixed  with  5  times  its  weight  of 
sulphuric  acid  and  heated,  evolves  carbon  dioxide  and  leaves  alcohol 
and  ammonium  hydrogen  sulphate  in  the  liquid. 

Ethyl  carbamate  heated  with  concentrated  potassium  hydroxide 
solution  yields  ammonium  hydroxide. 

A  solution  of  ethyl  carbamate  in  water,  mixed  with  sodium  carbonate 
and  a  little  iodine  and  warmed,  will  on  cooling  deposit  iodoform. 

Strong  solution  of  ethyl  carbamate  in  water  should  give  no  precipi- 
tate with  nitric  acid,  mercuric  nitrate  or  oxalic  acid. 

The  assay  of  ethyl  carbamate  can  be  carried  out  by  the  ordinary 
Kjeldahl  method.  One  hundred  parts  of  the  carbamate  will  yield 
51.7  parts  of  alcohol  and  19.1  parts  of  ammonia  (NH3). 

Amyl  Acetate.    Pentyl  acetate. 

Amyl  acetate  is  obtained  by  distilling  amyl  alcohols  with  an  acetate 
and  sulphuric  acid.  As  8  isomeric  forms  of  amyl  alcohol  exist,  the 
properties  of  the  acetate  will  differ  considerably  in  different  prepara- 
tions. The  isoamyl  form  is  generally  present  in  dominant  amount. 
It  is  a  colourless  liquid,  very  slightly  soluble  in  water,  but  soluble  in 
alcohol,  ether  and  amyl  alcohols.  It  boils  at  148°  and  has  a  sp.  gr.  of 
0.8963  at  o°. 

Amyl  acetate  may  be  determined  by  the  general  method  on  page 
237.  From  alcohol  it  may  be  separated  by  agitating  the  liquid  with  an 
equal  measure  of  saturated  solution  of  calcium  chloride  which  dissolves 
the  alcohol  only. 

Amyl  alcohols  may  be  separated  and  determined  approximately 
by  treating  the  sample  in  a  graduated  tube  with  a  mixture  of  equal 
volumes  of  glacial  acetic  acid  and  water. 

This  dissolves  amyl  alcohols,  but  leaves  amyl  acetate  insoluble 
(together  with  any  amyl  valerate  or  pelargonate  which  may  be  present) . 
By  first  separating  the  ethyl  alcohol  by  salt  water,  or  petroleum  spirit, 
this  method  may  be  applied  to  the  examination  of  the  essence  of 
jargonelle  pear. 


250  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

Amyl  Nitrite. 

Amyl  nitrite  is  prepared  by  processes  similar  to  those  employed  for 
obtaining  ethyl  nitrite,  amyl  alcohols  being  substituted  for  alcohol. 
To  obtain  a  product  fit  for  medicinal  use,  the  amyl  alcohols  should  be 
purified,  and  have  a  b.  p.  of  129°  to  132°. 

By  passing  vapour  of  nitrous  acid  (best  prepared  by  the  reaction  of 
nitric  acid  on  arsenous  oxide)  into  this  alcohol,  a  nearly  pure  nitrite  is 
obtained.  After  washing  the  product  with  water  and  solution  of  sodium 
carbonate  the  oily  liquid  is  rectified,  the  fraction  passing  over  between 
90°  and  100°  being  retained.  By  carefully  re-fractionating  the  distillate 
with  a  dephlegmator  (page  2 1 )  a  better  product  may  be  obtained,  but 
it  must  be  again  washed  with  sodium  carbonate  to  separate  traces  of 
acid  produced  by  decomposition  of  the  ether  during  redistillation. 

Isoamyl  nitrite  has  a  sp.  gr.  of  0.902,  and  boils  at  from  94°  to  95°. 
It  has  a  yellowish  colour,  penetrating  apple-like  odor,  pungent  aromatic 
taste,. and  produces  a  very  powerful  effect  on  the  system  when  its  vapour 
is  inhaled.  It  burns,  when  ignited,  with  a  fawn-coloured  smoky  flame. 

Amyl  nitrite  is  insoluble  in  water,  but  soluble  in  alcohol  in  all  pro- 
portions. It  also  dissolves  in  amyl  and  methyl  alcohols,  in  glacial 
acetic  acid,  and  is  miscible  in  all  proportions  with  ether,  chloroform, 
carbon  disulph  de,  benzene,  petroleum  spirit,  and  oils. 

In  contact  with  the  air,  and  apparently  more  readily  under  the 
influence  of  light,  amyl  nitrite  develops  an  acid  reaction  owing  to 
partial  decomposition.  Probably  this  change  occurs  more  readily  in 
presence  of  moisture. 

Concentrated  sulphuric  acid  attacks  amyl  nitrite  with  great  energy, 
red  fumes  being  evolved,  and  a  black,  foul-smelling  liquid  formed. 
Occasionally  the  mixture  inflames. 

A  characteristic  test  for  amyl  nitrite  is  the  formation  of  potassium 
valerate  when  the  liquid  is  dropped  on  melted  potassium  hydroxide. 
When  gently  warmed  with  excess  of  an  aqueous  solution  of  potassium 
hydroxide,  potassium  nitrite  is  formed,  and  a  stratum  of  amyl  alcohol 
floats  on  the  surface  of  the  liquid.  The  change  occurs  more  readily 
by  using  the  alcoholic  solution  and  subsequently  adding  water  to  cause 
the  separation  of  the  amyl  alcohol.  On  removing  the  aqueous  liquid, 
acidulating  it  with  acetic  acid,  and  adding  potassium  iodide,  the  nitrite 
will  occasion  an  abundant  liberation  of  iodine.  Griess'  test  can  also 
be  used  (page  241). 

When  amyl  nitrite  is  distilled  slowly  with  methyl  alcohol  it  is  com- 


ESTERS — COMPOUND    ETHERS.  251 

pletely  decomposed,  with  formation  of  amyl  alcohol  and  methyl  nitrite. 
Ethyl  alcohol  causes  a  less  complete  change,  but  it  is  evident  that 
an  alcoholic  solution  of  amyl  nitrite  would  be  liable  to  undergo 
decomposition. 

The  United  States  Pharmacopoeia  defines  Amyl  nitrite  to  be  a  liquid 
containing  about  80%  of  the  ester  (principally  isoamyl  nitrite)  when 
assayed  by  the  specified  method  (see  below).  The  sp.  gr.  of  the 
official  form  ranges  from  0.865  *°  0.875  at  25°- 

The  following  qualitative  tests  are  recommended: 

5  c.c.  of  the  sample  are  shaken  a  few  times  with  10  c.c.  of  water, 
i  c.c.  of  normal  potassium  hydroxide,  and  a  drop  of  phenolphthalein 
solution.  The  colour  of  the  liquid  should  not  be  entirely  discharged, 

A  mixture  of  1.5  c.c.  of  N/io  silver  nitrate  and  1.5  c.c.  of 
alcohol  with  a  few  drops  of  ammonium  hydroxide  should  not  become 
brown  or  black  if  mixed  with  i  c.c.  of  the  nitrite  and  gently  heated. 
This  is  the  method  suggested  for  detecting  aldehyde  which  would 
reduce  the  silver  salt. 

Commercial  Amyl  Nitrite. — The  amyl  nitrite  commonly  met  with 
is  sometimes  far  from  pure,  being  liable  to  contain  ethyl  and  amyl  alco- 
hols, amyl  nitrate,  butyl  and  hexyl  nitrites,  nitropentane,  valeric  alde- 
hyde, water,  and  other  bodies.  Amyl  nitrite  prepared  as  on  page  250, 
will  contain  most  of  these  in  only  very  insignificant  proportion,  but 
they  will  be  present  if  impure  fusel  oil  is  substituted  for  purified  amyl 
alcohol,  or  if  the  latter  is  converted  by  treatment  with  nitric  acid 
instead  of  nitrous  acid,  as  is  done  by  some  manufacturers. 

The  following  table  shows  the  composition,  densities,  and  b.  p.  of 
of  some  substances  likely  to  be  present  in  commercial  amyl  nitrite: 


Name. 

Sp.  gr. 

B.p. 

Nitropentane 

o  877 

i  ^o—  160 

Amyl  nitrite 

o  902  at  o°  C 

06 

Amyl  nitrate,  

i  .  ooo  at  7° 

yu 

148 

Amyl  alcohol,  

0.814  at  15° 

128—131 

Yaleraldehyde,                        

0.80^7  at  17° 

O2    ^ 

Valeraldehyde  is  not  likely  to  be  removed  by  fractional  distillation, 
though  the  other  impurities  can  be  more  or  less  eliminated.  Admix- 
ture of  valeric  aldehyde  or  amyl  alcohol  reduces  the  sp.  gr.  while  amyl 


252  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

nitrate  increases  it.  The  latter  has  a  comparatively  high  b.  p.,  hence  an 
instructive  examination  of  amyl  nitrite  can  be  made  by  distilling  the 
sample  with  a  dephlegmator  and  noting  the  volumes,  sp.  gr.  and  odours 
of  fractions  collected  at  different  temperatures.  A  fairly  pure  article, 
when  fractionally  distilled,  will  yield  at  least  80%  of  its  original 
measure  between  90°  and  100°,  and  should  leave  no  considerable  resi- 
due at  the  latter  temperature.  Some  specimens  have  been  found  to 
boil  at  temperatures  ranging  from  70°  to  180°,  and  occasionally  to 
leave  a  residue  at  220°.  As  a  rule,  incomplete  distillation  at  100°  is 
due  chiefly  to  the  presence  of  amyl  alcohol,  some  of  which  may  be  formed 
by  partial  decomposition  of  the  nitrite  during  distillation.  Hence 
commercial  amyl  nitrite  of  good  quality  may  leave  a  residue  of  5  to 
10%  at  100°. 

A  further  examination  of  the  nature  of  the  90°  to  100°  fraction 
might  be  made  by  gently  heating  it  for  some  time  with  methyl  alcohol 
in  a  flask  furnished  with  an  inverted  condenser.  On  subsequent  dis- 
tillation, the  fraction  passing  over  between  90°  and  100°  will  consist 
mainly  of  the  valeraldehyde  of  the  original  sample,  the  amyl  nitrite 
having  been  converted  into  amyl  alcohol  and  the  very  volatile  methyl 
nitrite. 

Nitropentane,  a  body  isomeric  with  amyl  nitrite,  appears  to  be  pres- 
ent in  most  commercial  specimens  of  the  latter,  and  sometimes  in 
notable  quantity.  It  may  be  detected  by  subjecting  the  fraction  dis- 
tilling between  140°  and  170°  to  the  action  of  nascent  hydrogen  when 
amylamine,  will  be  formed,  and  may  be  recognised  by  the  alkaline 
character  of  the  distillate  obtained  on  boiling  with  potassium  hy- 
droxide. Nitropentane  may  also  be  detected  by  dissolving  the  140°  to 
1 70°  fraction  in  solution  of  potassium  hydroxide,  adding  a  little  sodium 
nitrite,  and  then  dilute  sulphuric  acid  very  cautiously,  when  a  blood- 
red  colouration  will  be  produced,  which  disappears  when  the  solution 
becomes  acid.  Pentyl  nitrolic  acid  is  produced  and  may  be  extracted 
by  agitation  with  ether.  Probably  the  test  might  be  applied  by  warm- 
ing the  original  sample  with  alcoholic  potassium  hydroxide  and  cau- 
tiously adding  dilute  sulphuric  acid. 

Amyl  Nitrate,  if  present,  will  be  contained  in  the  last  fractions 
obtained  on  distilling  a  sample  of  amyl  nitrite. 

Valeric  Aldehyde,  may  be  detected  by  treating  the  sample  with 
three  measures  of  a  mixture  in  equal  parts  of  strong  ammonium 
hydroxide  and  absolute  alcohol,  then  adding  a  few  drops  of  silver- 


ALDEHYDES.  253 

nitrate  solution  and  warming  gently,  when  a  dark  brown  will  be 
produced  if  valeric  aldehyde  be  present. 

Butyl  and  hexyl  compounds  may  be  detected  by  saponifying  the 
sample  with  sodium  hydroxide  and  examining  the  amyl  acohol  layer 
for  butyl  and  hexyl  alcohols  by  distillation. 

Free  acid  may  be  detected  and  estimated  as  in  spirit  of  nitrous 
ether  after  dissolving  the  sample  in  rectified  spirit. 

Water  increases  the  sp.  gr.  of  the  preparation,  and  renders  it  turbid 
in  melting  ice.  The  presence  of  water  increases  the  tendency  to 
decomposition. 

Hydrogen  cyanide,  occasionally  present  as  a  by-product,  may  be 
recognised  by  largely  diluting  the  sample  with  alcohol  and  adding 
silver  nitrate,  when  white  curdy  silver  cyanide  will  be  precipitated. 

The  United  States  Pharmacopoeia  process  for  assay  of  amyl  nitrite 
is  the  same  as  that  for  ethyl  nitrite  (page  245)  except  that  3  c.c.  of 
the  sample  are  shaken  with  potassium  hydrogen  carbonate  and  then 
decanted  and  weighed  in  the  tared  100  c.c.  flask.  The  reading  of  the 
volume  of  gas  multiplied  by  4.8  and  divided  by  the  weight  of  sample 
taken  gives  the  percentage  of  nitrite  present  at  25°  and  760  mm. 
Corrections  for  difference  of  temperature  and  pressure  are  made  ac- 
cording to  the  rule  for  assay  of  ethyl  nitrite. 

ALDEHYDES. 

The  aldehydes  are  a  series  of  compounds  intermediate  in  composition 
between  the  alcohols  and  their  corresponding  acids. 

Aldehydes  result  from  the  treatment  of  the  corresponding  alcohols 
by  oxidising  agents  of  moderate  power,  such  as  dilute  nitric  acid  or 
dilute  chromic  acid  mixture  used  cautiously.  They  are  also  formed 
by  distilling  a  mixture  of  the  sodium  or  calcium  salt  of  the  correspond- 
ing acid  with  calcium  formate. 

Aldehydes  may  also  be  obtained  by  the  action  of  nascent  hydrogen 
on  the  chlorides  of  the  corresponding  acid  radicles,  and  by  various 
other  reactions. 

When  pure,  the  aldehydes  may  apparently  be  preserved  without 
change,  but  the  presence  of  mere  traces  of  impurity  (e.  g.,  mineral 
acids),  tends  to  cause  their  gradual  conversion  into  polymers  or  con- 
densation-products, in  the  latter  case  water  being  simultaneously 
eliminated. 


254  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

By  oxidation,  the  aldehydes  are  very  readily  converted  into  the  corre- 
sponding acids.  Hence,  they  are  powerful  reducing  agents,  precipi- 
tating metallic  silver  from  the  ammonio-nitrate  and  decolourising 
permanganates. 

By  the  action  of  nascent  hydrogen  (sodium  amalgam),  the  aldehydes 
are  reduced  to  the  corresponding  alcohols,  but  the  fixation  of  hydrogen 
is  often  attended  with  condensation,  and  consequent  coformation  of  a 
higher  diatomic  alcohol. 

When  heated  with  solutions  of  alkalies,  the  aldehydes  are  mostly 
converted  into  resinous  bodies.  By  fusion  with  potassium  hydroxide 
aldehydes  are  converted  into  the  potassium  salts  of  the  corresponding 
acids,  hydrogen  being  simultaneously  evolved;  in  some  cases  this  acts 
on  another  portion  of  the  aldehyde  and  converts  it  into  the  correspond- 
ing alcohol. 

Many  of  the  aldehydes  form  compounds  with  water,  hydrogen 
chloride  and  other  bodies,  but  the  products  are  very  unstable. 

The  aldehydes  readily  combine  with  ammonia  (NH3),  the  products 
first  formed  often  undergoing  molecular  condensation  more  or  less 
rapidly.  The  ammonia  compounds  of  the  aldehydes  of  the  acetic 
series  are  not  liable  to  this  change,  and  are  stable  crystalline  bodies 
which  liberate  the  original  aldehyde  on  treatment  with  dilute  sulphuric 
acid. 

Many  aldehydes  and  allied  bodies  (ketones),  have  the  property  of 
forming  stable  crystalline  compounds  with  acid  sulphites.  The 
sodium  compound  is  readily  obtained  on  treating  the  aldehyde  or  its 
aqueous  solution  with  excess  of  a  saturated  cold  solution  of  sodium 
hydrogen  sulphite,  when  the  compound  separates  in  crystals  which 
are  soluble  in  water  or  alcohol,  but  insoluble  in  a  strong  solution  of 
the  reagent.  From  this  compound  the  aldehyde  may  be  regenerated 
by  treatment  with  dilute  sulphuric  acid  (or  sodium  carbonate),  or 
sometimes  by  simply  warming  the  aqueous  solution.  Aldehydes  of 
the  acetic  series  (as  also  chloral)  reduce  hot  Fehling's  solution,  but 
aldehydes  of  the  aromatic  series  do  not. 

Most  substances  of  the  aldehyde  class  give  colouration  with  an  acid 
solution  of  rosaniline  previously  mixed  with  sufficient  sodium  sulphite 
almost  to  decolourise  it.  (See  page  257.)  Examined  in  this  way, 
acetaldehyde,  paraldehyde,  and  propionaldehyde  give  an  intense  red- 
violet  colouration.  Chloral  gives  at  once  a  fine  colour,  but  chloral 
hydrate  gives  no  reaction.  Acrolein  and  butyl  chloral  produce  a  violet 


ALDEHYDES.  255 

colour  on  shaking.  Furfural  and  benzaldehyde  give  the  colour  more 
readily.  Salicylic  and  cuminic  aldehydes  react  well  after  some  agita- 
tion. Cinnamic  aldehyde  and  furfur-acrolein  give  at  first  an  intense 
yellow  colour,  soon  changing  to  violet-red.  Acetone  readily  reacts  on 
shaking,  but  acetophenone  and  benzophenone  have  no  action.  Methyl 
and  ethyl  alcohols  give  a  faint  violet  colour  on  shaking,  propylic  and 
isopropylic  alcohols  a  scarcely  perceptible  reaction,  while  with  their 
higher  homologues,  and  phenols,  glycols,  quinine,  sugars,  and  formic 
acid,  no  colour  is  obtained. 

A  mere  trace  of  most  bodies  of  the  aldehyde  class  produces  a  fine 
scarlet  colour  with  a  solution  of  phenol  in  excess  of  sulphuric  acid,  the 
colour  changing  to  a  dark  red  on  warming  the  mixture. 

A  delicate  test  for  aldehydes  is  the  violet-red  colour  they  give 
with  diazobenzene-sulphonic  acid  in  presence  of  free  alkali,  i  part 
of  freshly-prepared  diazobenzene-sulphonic  acid  is  dissolved  in  60 
parts  of  cold  water  rendered  alkaline  by  sodium  hydroxide.  To 
this  solution  is  added  the  liquid  to  be  tested  (previously  mixed  with 
dilute  solution  of  sodium  hydroxide)  together  with  a  little  sodium 
amalgam.  If  an  aldehyde  be  present,  an  intense  violet-red  is  pro- 
duced, either  immediately  or  within  20  minutes.  The  colour  is 
destroyed  by  long  exposure  to  the  air,  and  is  changed  by  the  addition 
of  an  acid. 

The  reaction  is  readily  yielded  by  a  solution  containing  i  part  in 
3,000  of  benzaldehyde  (oil  of  bitter  almonds),  and  has  been  obtained 
with  acetic,  valeric,  and  cenanthic  aldehydes,  as  also  with  furfural 
and  glyoxal.  Chloral  and  benzoin  do  not  give  the  reaction.  Acetone 
and  ethyl  aceto-acetate  give  a  red  colour,  but  without  the  violet  tint 
characteristic  of  an  aldehyde.  The  reaction  is  not  produced  by  phenol, 
resorcinol,  or  pyrocatechol  (if  care  be  taken  to  have  excess  of  alkali 
present),  but  is  given  by  dextrose.  It  is  said  to  be  more  delicate  than 
that  with  rosaniline  reduced  with  sulphurous  acid;  but  the  reaction  is 
more  especially  suitable  for  the  detection  of  aldehydes  which  are  per- 
manent in  alkaline  solutions. 

E.  Fischer  recommends  the  employment  of  phenylhydrazine  hydro- 
chloride  as  a  reagent  for  detecting  bodies  of  the  aldehyde  class. 

The  ammoniated  silver  solution  described  on  page  265  is  a  general 
test  for  aldehydes. 

Acrolein,  valeral,  furfural  and  the  essential  oils  of  bitter  al- 
monds, cinnamon,  cloves,  cumin,  and  meadow-sweet  have  the  consti- 


256  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

tution  and  characters  of  aldehydes.  All  these  form  crystalline  com- 
pounds with  acid  sulphites. 

Acetone  and  acetal  are  bodies  allied  to  the  aldehydes,  and  chloral 
is  a  trichloraldehyde. 

According  to  Ripper,  (Monatsh.  d.  Chem.,  1900,  21,  1079),  any 
aldehyde  soluble  in  water  or  in  very  dilute  alcohol  can  be  assayed  as 
follows:  (See  page  266.) 

A  convenient  amount  of  the  solution  of  the  aldehyde  is  mixed  with 
twice  its  bulk  of  a  solution  of  acid  potassium  sulphite  (containing  12 
grm.  in  icooc.c.)  The  mixture  is  allowed  to  stand  for  15  minutes, 
and  the  unprecipitated  sulphite  determined  by  titration  with  iodine. 
The  sulphite  solution  must,  of  course,  be  valued  by  a  similar  titration. 

Formic  Aldehyde.     Formaldehyde.     Methaldehyde. 

This  body  is  produced  by  the  limited  oxidation  of  methyl  alcohoL 
Its  formation  is  the  first  stage  in  the  production  of  carbohydrates  in 
plants  by  the  decomposition  of  carbon  dioxide,  hydrogen  dioxide  being 
produced  at  the  same  time.  It  presents  a  general  resemblance  to 
ordinary  or  acetic  aldehyde,  but  it  is  polymerised  with  exteme  readi- 
ness. It  is  gaseous  at  the  ordinary  temperature,  a  polymer,  para- 
formaldehyde,  is  a  white  insoluble  body,  subliming  at  the  tempera- 
ture of  boiling  water,  and  suffering  depolymerisation  at  a  higher  tem- 
perature, or  when  heated  to  140°  with  excess  of  water  in  a  sealed  tube. 

Ordinary  formaldehyde  undergoes  slow  oxidation  in  the  air,  forming 
formic  acid.  It  is  rapidly  oxidised  by  the  more  powerful  oxidising 
agents.  When  its  aqueous  solution  is  mixed  with  solid  potassium 
permanganate,  a  violent  reaction  occurs,  some  of  the  aldehyde  is  oxi- 
dised to  carbon  dioxid  and  water,  and  another  portion  escapes  in  the 
form  of  vapor.  The  gases  eliminated  are  often  combustible.  Thi- 
reaction  has  been  utilised  for  obtaining  formaldehyde  vapour  in  disins 
fecting  large  inclosed  spaces,  for  which  it  is  especially  applicable. 
The  danger  of  fire  from  the  spontaneous  ignition  of  the  evolved  gases 
must  be  kept  in  mind. 

Formaldehyde  reacts  with  ammonium  hydroxide  forming  a  sub- 
stitution amine  (see  page  263)  When  heated  with  sodium  hydroxide 
for  some  time  on  the  water-bath,  formaldehyde  forms  sodium  formate 
and  methyl  alcohol. 

The  solid  polymer  is  no'w  sold  under  the  name  "paraform"  for  dis- 
infecting purposes.  This  material  begins  to  sublime  at  100°  and 
melts  between  153°  and  172°,  producing  gaseous  formaldehyde. 


FORMALDEHYDE.  257 

The  United  States  Pharmacopoeia  solution  of  formaldehyde  (Liquor 
jormaldehydi)  istrequired  to  contain  not  less  than  37%  by  weight  of 
the  aldehyde.  The  sp.  gr.  of  this  solution  ranges  from  1.075  t°  1.081 
at  25°.  It  should  not  contain  more  than  0.2%  of  free  acid,  calcu- 
lated as  formic. 

Formaldehyde  has  acquired  great  importance  within  the  last  few 
years  on  account  of  its  employment  as  a  disinfectant  and  food  pre- 
servative. The  literature  concerning  it  is  extensive,  much  of  it  relates  to 
the  detection  of  the  substance  in  food,  especially  milk.  It  is  princi- 
pally sold  as  a  40%  (by  volume)  solution  in  water,  under  the 
name  "formalin."  Formaldehyde  forms  compounds  with  many 
albuminous  and  gelatmous  substances,  often  rendering  them  very  in- 
soluble. A  few  drops  of  formalin  added  to  a  solution  of  gelatin  cause 
the  liquid  to  set  to  a  mass  which  cannot  be  melted  when  held  in  a 
flame.  The  compounds  obtained  in  this  manner  retain  to  some  extent 
the  properties  of  formaldehyde. 

When  solutions  of  formaldehyde  are  boiled,  a  considerable  portion 
of  the  substance  passes  over  with  the  steam,  but  if  the  distillate  be 
transferred  to  a  dish  on  the  steam-bath  and  evaporated,  much  of  the 
substance  will  remain  as  a  white  solid — the  polymeric  modification. 

Many  tests  for  formaldehyde  have  been  published.  Some  of  these 
are  general  tests  for  the  aldehydes  (see  p.  253).  The  following  are 
mostly  of  this  character,  but  they  are  especially  employed  for  the  detec- 
tion of  formaldehyde. 

Fuchsin  Test.— This  is  performed  with  Schiff's  reagent,  for  the 
preparation  of  which  Allen  suggested  the  following:  40  c.c.  of  a 
5%  solution  of  magenta  (fuchsin)  are  mixed  with  250  c.c.  of 
water,  10  c.c.  of  sodium  acid  sulphite  solution  of  1.375  SP'  gr->  an<^ 
then  10  c.c.  of  pure  sulphuric  acid.  The  mixture  is  allowed  to  stand 
for  some  time,  when  it  will  become  colourless.  The  addition  of  a  solu- 
tion of  formaldehyde  restores  the  red  of  the  dye,  but  a  colour  resembling 
that  caused  by  formaldehyde  may  be  obtained  by  blowing  air  through 
the  reagent,  by  contact  with  aerated  water  or  even  by  warming. 

Betanaphthol  Test  (Mulliken,  Ident.  Pure  Org.  Comp.,  vol.  i).— 
The  solution  to  be  tested  is  mixed  with  3  c.c.  of  dilute  alcohol  (1:2), 
0.005  grm-  betanaphthol  and  3  to  5  drops  of  hydrochloric  acid  and 
boiled  for  few  minutes.  Any  precipitate  is  collected  on  a  filter  washed 
with  dilute  alcohol  of  the  same  strength  as  that  first  used,  dissolved  in 
a  small  amount  of  alcohol  by  the  aid  of  heat,  the  liquid  cooled,  the 
VOL.  1—17 


258  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

crystals  that  separate  collected  on  a  filter  washed  with  i  c.c.  of  strong 
alcohol  dried  on  a  porous  tile  in  a  warm  place  and  the  m.  p.  deter- 
mined. The  precipitate  when  formaldehyde  is  present  is  methylene- 
dibetanaphthol  (CH2)(C10H6HO)2),  melting  at  189°. 

Salicylic  acid  Test. — A  small  amount  of  salicylic  acid  is  dissolved 
in  a  few  c.c.  of  strong  sulphuric  acid.  When  this  mixture  is  warmed 
gently  with  formaldehyde  a  red  liquid  is  produced. 

Phenylhydrazine-nitroprusside  Test. — Rimini's  test.  A  small 
amount  of  phenylhydrazine  hydrochloride  is  added  to  the  solution  to 
be  tested,  then  a  drop  of  dilute  solution  of  sodium  nitroprusside  and 
a  few  drops  of  sodium  hydroxide  solution.  The  liquid  becomes  deep 
blue  if  formaldehyde  is  present.  The  nitroprusside  solution  should  be 
freshly  prepared.  With  milk  containing  formaldehyde  this  test  pro- 
duces a  greyish-green. 

Phloroglucol  Test. — A  small  amount  of  a  freshly  prepared  (about 
i  %)  solution  of  phloroglucol  in  water  is  mixed  with  an  equal  meas- 
ure of  a  25  %  solution  of  sodium  hydroxide,  and  the  solution  to  be 
tested  added.  The  liquid  becomes  rose-red.  It  is  best  to  introduce 
the  liquid  to  be  tested  by  means  of  a  pipette,  so  as  to  underlay  the  rea- 
gent solution.  The  color  then  appears  at  the  junction  of  the  liquids. 

Hydrochloric  Acid  Test.— i  c.c.  of  hydrochloric  acid  containing 
a  little  iron  is  added  to  4  c.c.  of  the  liquid  to  be  tested  and  the  mixture 
heated  to  boiling.  If  formaldehyde  is  present  the  liquid  will  become 
red.  The  test  does  not  work  well  if  much  formaldehyde  is  present.  If 
the  liquid  becomes  yellow  on  heating,  some  of  the  original  solution 
should  be  considerably  diluted  and  the  test  repeated.  Many  samples  of 
commercial  hydrochloric  acid  contain  enough  iron  to  give  the  reaction. 
Pure  acid  may  be  made  applicable  by  adding  ferric  chloride  in  the  pro- 
portion of  0.025  grm-  to  100  c.c. 

Bonnet's  Test  (/.  Amer.  Chem.  Soc.,  1905,  27,  601). — A  small 
amount  of  morphine  is  placed  on  a  watch-glass,  a  drop  or  two  of  sul- 
phuric acid  added,  the  mass  stirred  with  a  glass  rod,  and  the  watch-glass 
floated  on  the  surface  of  the  liquid  to  be  tested.  The  whole  is  then 
covered  with  a  glass  or  porcelain  cover  and  allowed  to  remain  for  at 
least  thirty  minutes.  If  formaldehyde  is  present  the  mixture  in  the 
dish  will  become  dark. 

This  test  has  the  advantage  that  the  reaction  can  only  be  due  to  a 
volatile  ingredient,  and  the  interfering  or  misleading  reactions  of  sub- 
stances in  complex  organic  mixtures,  such  as  milk,  are  avoided. 


FORMALDEHYDE.  259 

The  dimethylaniline  test,  suggested  by  Trillat,  and  described  in 
the  previous  edition  of  this  work,  has  been  shown  by  B.  M.  Pilhashy 
(/.  Amer.  Chem.  Soc.,  1899,  21,  134)  to  be  untrustworthy,  the  colour 
reaction  being  due  to  the  reagents: 

Resorcinol  Test  (Lebbin). — A  few  c.c.  of  the  liquid  to  be  tested 
are  boiled  with  0.05  grm.  of  resorcinol,  to  which  half  or  an  equal  volume 
of  a  50  %  solution  of  sodium  hydroxide  is  added.  If  formaldehyde  is 
present,  the  yellow  solution  changes  to  a  fine  red.  Analogous  com- 
pounds showing  the  usual  reactions  characteristic  of  alhedydes  fail 
to  give  this  colouration. 

Phenol  Test  (Hehner). — If  to  an  aqueous  solution  of  formaldehyde 
one  drop  of  a  dilute  aqueous  solution  of  phenol  be  added,  and  the 
mixture  be  poured  upon  some  strong  sulphuric  acid  in  a  test-tube,  a 
bright  crimson  zone  appears  at  the  point  of  contact  of  the  two  liquids. 
The  reaction  must  be  carried  out  as  described.  A  trace  only  of 
phenol  must  be  used,  and  it  must  be  first  mixed  with  the  solution  to  be 
tested  before  adding  to  the  sulphuric  acid. 

Milk  Test  (Hehner). — Milk  containing  formaldehyde  produces  with 
strong  sulphuric  acid  a  purple-violet  liquid.  The  test  is  best  applied 
by  underlaying  the  milk  with  the  acid,  when  the  colour  is  seen  just 
below  the  line  of  junction.  The  acid  must  contain  a  trace  of  iron, 
which  can  be  easily  secured  by  adding  a  drop  or  two  or  ferric  chloride 
to  5  c.c.  of  the  pure  acid.  Good  results  are  obtained  by  putting  a 
few  crystals  of  potassium  sulphate  into  the  milk  before  underlaying 
it  with  the  acid. 

Shrewsbury-Knapp  Test  (Analyst,  1909,  34,  12). — H.  S.  Shrews- 
bury and  A.  W.  Knapp  find  that  a  reagent  prepared  by  mixing 
1.6  c.c.  of  N/i  nitric  acid  and  100  c.c.  of  concentrated  hydrochloric 
acid  produces  violet  with  very  minute  quantities  of  formaldehyde 
in  milk.  The  reagent  must  be  freshly  prepared.  10  c.c.  of  it  are 
added  to  5  c.c.  of  the  milk  in  a  test-tube,  the  tube  placed  in  a  water- 
bath  at  a  constant  temperature  of  50°  for  10  minutes,  then  cooled 
rapidly  to  15°.  Quantitative  estimations  can  be  made  by  comparing 
the  color  with  that  produced  by  milk  containing  known  amounts  of 
formaldehyde.  If  the  depth  of  colour  produced  by  the  sample  is 
deeper  than  produced  by  6  parts  per  million  of  formaldehyde,  it  is 
best  to  dilute  the  sample  and  make  a  new  test. 

The  observers  found  that  the  most  delicate  quantitative  reactions 
were  obtained  with  milks  containing  from  0.2  to  6.0  parts  per  million. 


260  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

Several  other  oxidizing  agents  were  tried  by  them,  but  were  found  to 
be  inferior  to  nitric  acid.  They  consider  that  the  dyes  occasionally 
used  in  adulterating  milk  will  not  interfere  with  the  test. 

C.  H.  LaWall  (Proc.  Pa.  Pharm.  Assn.,  1905,  200)  found  that  vanillin 
simulates  formaldehyde  in  the  sulphuric  acid  contact  test,  the  resorcinol 
test,  and  the  phenol-sulphuric  acid  test.  As  vanillin  is  often  used  in 
association  with  foods  that  are  likely  to  be  preserved  with  formalde- 
hyde, care  must  be  taken  not  to  overlook  this  simulation.  Lawall  found 
that  the  phenylhydrazin  test  does  not  react  with  vanillin. 

QUANTITATIVE   METHODS. 

The  tests  for  formaldehyde  are  best  applied  to  pure  solutions  in 
water.  As  the  substance  is  readily  volatile  with  steam,  some  of  it 
can  usually  be  obtained  in  satisfactory  form  by  simple  distillation,  but 
the  amount  that  passes  over  is  uncetain  and  it  is  often  impossible  to 
obtain  a  distillate  containing  all  the  formaldehyde.  The  esrimation  of 
the  small  quantities  employed  for  preserving  milk  is  especially  at- 
tended with  great  difficulty.  The  preliminary  isolation  of  the  pre- 
servative by  distilling  the  milk  is  open  to  objection,  but  the  experiments 
made  by  Leonard  and  Smith  (Analyst,  1897,  22,  5)  show  that  rough 
indications  of  the  amount  of  formaldehyde  present  can  be  obtained 
with  certain  precautions:  (i)  The  distillate  from  fresh  milk  exerts 
no  appreciable  reducing  action  on  alkaline  permanganate,  but  n^ilk 
3  or  4  days  old  yields  a  distillate  having  marked  reducing  properties. 
(2)  The  separation  of  formaldehyde  from  milk  is  facilitated  by 
acidifying  the  liquid  with  sulphuric  acid  and  blowing  live  steam 
through  it.  Under  these  conditions  the  first  20  c.c.  of  distillate  from 
100  c.c.  of  milk  will  contain  about  1/3  and  the  first  40  c.c.  about  1/2 
of  the  total  amount  of  formaldehyde  present.  (3)  The  fact  that 
the  distillate  from  milk  does  not  contain  the  whole  of  the  formalde- 
hyde present  is  to  a  great  extent  explained  by  the  behaviour  of  solutions 
of  formaldehyde  on  distillation,  and  is  only  partly  due  to  any  specific 
action  of  the  preservative  on  the  constituents  of  milk. 

Several  methods  of  assay  have  been  suggested,  some  of  which  are  de- 
scribed below.  ,  According  to  R.  H.  Williams  (/.  Amer.  Chem.  Soc., 
1905,  27,  596),  the  iodine  method  is  best  adapted  to  pure  dilute  solu- 
tions; the  potassium  cyanide  method  to  impure  dilute  solutions;  the 
hydrogen  peroxide  method,  directed  by  the  United  States  Pharmaco- 
poeia, to  strong  impure  solutions. 


FORMALDEHYDE.  261 

lodiometric  Method  (Romijn,  Zeit.  Anal.  Chem.,  1897,36,  18. — 10 
c.c.  of  the  solution  to  be  tested  are  mixed  with  25  c.c.  of  decinormal 
iodine  and  sodium-hydroxide  solution  added,  drop  by  drop,  until  the 
liquid  becomes  clear  yellow.  After  ten  minutes  hydrochloric  acid  is 
added  and  the  free  iodine  is  titrated  with  decinormal  sodium  thiosul- 
phate.  Two  atoms  of  iodine  are  equivalent  to  i  molecule  of  for- 
maldehyde. This  method  is  suitable  for  the  accurate  determination  of 
formaldehyde  alone,  but  does  not  give  good  results  in  the  presence 
of  other  aldehydes  and  ketones. 

Potassium  Cyanide  Method. — This  is  based  upon  the  fact  that 
formaldehyde  combines  with  potassium  cyanide.  The  addition-prod- 
uct reduces  silver  nitrate  in  the  cold,  but  if  the  silver  nitrate  be  acidi- 
fied with  nitric  acid  before  the  addition  of  the  aldehyde  mixture,  no  pre- 
cipitate results  if  the  aldehyde  in  the  latter  be  in  excess.  If,  on  the 
other  hand,  the  cyanide  is  in  excess,  one  molecule  of  potassium  cyanide 
is  left  in  combination  with  one  molecule  of  the  formaldehyde,  while  the 
excess  precipitates  silver  cyanide  from  the  silver  nitrate  solution. 

10  c.c.  of  decinormal  silver  nitrate,  acidified  with  nitric  acid,  are 
mixed  with  10  c.c.  of  potassium-cyanide  solution  (prepared  by  dissolv- 
ing 3.1  grms.  of  the  96  %  salt  in  500  c.c.  of  water),  the  whole  diluted  to 
500  c.c.,  filtered,  and  25  c.c.  of  the  filtrate  titrated  by  Volhard's  method. 
The  difference  between  this  blank  result  and  that  obtained  by  titrat- 
ing the  filtrate  after  the  addition  of  the  aldehyde  solution  gives  the 
amount  of  decinormal  sulphocyanate  corresponding  to  the  silver  not 
precipitated  by  the  excess  of  potassium  cyanide.  From  this  the  amount 
of  formaldehyde  can  be  calculated.  Results  by  this  method  are  said 
to  be  correct,  even  in  the  presence  of  acetaldehyde,  if  titrated  imme- 
diately after  shaking. 

Hydrogen  Peroxide  Method. — Blank  and  Finkenbeiner  first 
described  this  method  (Ber.,  1893,  31,  2979).  It  was  further  studied 
by  Fresenius  and  Griinhut  (Zeit.  anal.  Chem.,  1905,  44,  13).  R.  H. 
Williams  (/.  Amer.  Chem.  Soc.,  1905,  27,  596)  and  J.  K.  Hay  wood 
and  B.  H.  Smith  (/.  Amer.  Chem.  Soc.,  1905,  27,  1183).  The  last- 
mentioned  workers  give  the  process  substantially  as  given  by  the 
U.  S.  Pharmacopoeia,  but  advise  taking  the  sp.  gr.  of  the  formaldehyde 
solution  and  calculating  the  weight  of  a  definite  volume  while  the 
U.  S.  P.  directs  the  weighing  of  the  amount  of  solution  used.  The 
U.  S.  P.  process  is  here  given. 

3  c.c.  of  the  solution  are  weighed  accurately  in  a  well-stoppered 


262  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

Erlenmeyer  flask,  50  c.c.  of  normal  sodium  hydroxide  are  added,  the 
liquids  mixed  and  50  c.c.  solution  of  hydrogen  peroxide  added  "imme- 
diately, but  slowly,  through  a  small  funnel."  Previous  to  addition,  the 
hydrogen  peroxide  should  have  been  exactly  neutralised  by  normal 
sodium  hydroxide,  using  litmus  as  an  indicator.  The  addition  of  the 
hydrogen  peroxide  will  cause  foaming.  When  this  has  ceased,  rinse 
the  funnel  and  the  sides  of  the  flask  with  distilled  water,  allow  to  stand 
for  30  minutes  and  titrate  to  neutrality  with  normal  sulphuric  acid. 
The  number  of  c.c.  of  alkali  consumed  by  the  formic  acid  produced 
by  the  oxidation,  multiplied  by  2.979  and  divided  by  the  weight  of 
solution  taken  will  give  the  percentage  by  weight  of  absolute  formalde- 
hyde present.  The  hydrogen  peroxide  should  be  the  standard,  10 
volumes  (about  3%),  solution. 

Ammonia  Method.— A.  G.  Craig  (/.  Amer.  Chem.  Soc.  1901,  23, 
642)  finds  that  the  reaction  between  ammonia  and  formaldehyde  (see 
page  263)  can  be  used  according  to  the  following  manipulation: 

Several  stout  bottles  holding  about  100  c.c.  and  provided  with  good 
rubber  stoppers  are  selected,  and  a  vessel  that  will  allow  them  to  be 
submerged  while  standing  upright.  In  each  of  the  bottles  is  placed 
25  c.c.  of  normal  ammonium  hydroxide  (it  is  not  necessary  that  this 
should  be  exactly  of  that  strength).  In  some  of  the  bottles  accurately 
measured  amounts  of  the  solution  to  be  tested  are  placed,  using  a  quan- 
tity containing  about  0.5  grm.  of  the  aldehyde. 

The  bottles  are  securely  corked,  tied  down,  placed  in  the  heating 
vessel,  submerged  with  cold  water  and  the  latter  raised  to  the  b.  p. 
Water  must  be  added  cautiously  from  time  to  time,  keeping  the  bottles 
submerged  and  upright.  After  being  in  the  bath  for  i  hour,  they  are 
removed,  cooled,  opened,  a  little  methyl  orange  added  to  each  and 
then  each  titrated  with  normal  sulphuric  acid  until  the  first  red  tint 
appears.  The  difference  between  the  amount  of  acid  required  for  the 
blanks  and  that  for  the  bottles  in  which  the  formaldehyde  solution  was 
placed  is  the  equivalent  of  the  ammonia  used  by  the  latter.  One  c.c.  of 
normal  ammonium  hydroxide  is  taken  up,  0.0601  of  by  formaldehyde. 

Gasometric  Method. — G.  B.  Frankforter  and  R.  West  (/.  Amer. 
Chem.  Soc.  1905,  27,  714)  find  that  estimation  of  formaldehyde  may 
be  made  by  measuring  the  gas  evolved  when  hydrogen  dioxide  is 
added  to  a  mixture  of  formaldehyde  and  potassium  hydroxide.  The 
reaction  is 


HEXAMETHYLENE-TETRAMINE.  263 

Hexamethylene-tetramine.  Hexamethylene-amine.  (CH2)6N4. 
—This  body  is  a  substitution  amine  (tetramine),  but  as  it  is  a  direct 
product  from  formaldehyde  and  owes  its  importance  entirely  to  its 
therapeutic  relation  to  that  substance,  it  will  be  described  here.  It  is 
produced  by  the  action  of  formaldehyde  on  ammonia,  the  equation 
reaction  being 

6CH20  +  4NH3  =  (CHa)6N4  +  6H2O. 

The  compound  forms  colourless,  odourless,  glistening  crystals,  solu- 
ble in  about  1.5  parts  of  water,  both  cold  and  boiling,  10  parts  of 
alcohol,  and  sparingly  in  ether.  The  solution  in  water  is  alkaline  to 
litmus;  the  tannin  and  mercuric  chloride  give  precipitates  with  it. 
The  solid  is  volatilised  and  partially  decomposed  by  heating.  Strong 
sulphuric  acid  converts  it  into  ammonium  sulphate  and  formaldehyde. 
A  mixture  of  it  with  a  little  salicylic  acid  becomes  red  on  warming 
with  sulphuric  acid. 

This  substance  is  used  especially  as  a  means  of  introducing  for- 
maldehyde into  the  genito-urinary  tract,  in  the  treatment  of  sup- 
purative  diseases  of  the  kidneys,  bladder  and  urethra.  It  is  appar- 
ently partly  hydrolysed  in  the  system,  reproducing  formaldehyde  and 
ammonium  hydroxide.  The  former  is  excreted  with  the  urine.  The 
compound  is  now  sold  under  many  proprietary  names,  among  which 
are  ''urotropin,"  "formin,"  "cystogen." 

In  addition  to  the  tests  above  given  ,  an  assay  of  a  sample  could  read- 
ily be  made,  by  the  Kjeldahl-Gunning  method.  The  pure  substance 
contains  40  per  cent,  of  nitrogen. 

The  frequent  use  of  hexamethylene  amine  in  proprietary  medicines 
and  nostrums  renders  it  necessary  to  note  some  processes  especially 
adapted  to  detecting  it  in  such  articles.  Horton  (Ber.,  1888,  21,  2000) 
found  that  bromine  forms  a  brick-red  precipitate,  having  the  composi- 
tion C6H12N4Br4,  which  on  drying  becomes  yellow  and  is  converted 
into  the  dibromide,  C6H12N4Br2.  Dobriner  (Zeit.  anal.  Chem., 
1897,  36,  44)  found  that  mercuric  chloride  produces  precipitates 
which  differ  with  the  ratio  of  the  reagent  to  the  hexamethylene-amine, 
when  the  latter  is  excess,  the  precipitate  consists  of  monoclinic  prisms 
containing  2C6H12N4  +3HgCl2,  but  when  the  reagent  is  in  excess  the 
compound  C6HI2N4  +  6HgCl2  is  formed. 

The  bromine  and  mercuric  chloride  compounds  may  be  further 
tested  for  identification.  The  dibromide  melts  slightly  below  200°. 


264  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

The  amounts  of  bromine  and  nitrogen  present  may  be  ascertained  by 
the  usual  methods.  In  the  case  of  the  mercuric  chloride  compound, 
which  should  be  obtained  by  using  excess  of  the  reagent,  the  propor- 
tions of  mercury  and  chlorine  will  be  important  data. 

Separation  of  Formaldehyde  and  Acetaldehyde. — Mulliken  and 
Scudder  have  described  the  following  method: 

A  round-bottom  flask  is  connected  with  a  long  spiral  reverse  con- 
denser, through  which  water  at  from  45°  to  50°  is  passed.  The  upper 
part  of  the  spiral  is  connected  tightly  with  a  tube  which  turns  and  is 
connected  to  a  descending  spiral  condenser  which  is  surrounded  with 
ice  and  salt  and  is  tightly  connected  to  a  flask,  also  immersed  in  a 
freezing  mixture.  All  the  condensing  apparatus  should  be  of  glass. 
A  suitable  amount  of  the  aldehyde  mixture  is  placed  in  the  distilling 
flask  and  gently  boiled  for  two  hours.  Only  traces  of  formaldehyde 
pass  into  the  receiver,  but  the  acetaldehyde  distils  over.  The  liquid 
to  be  distilled  should  not  contain  over  i  per  cent,  of  formaldehyde. 

Acetaldehyde.     Acetic  Aldehyde.     Ethyl  Aldehyde. 

This  is  the  body  from  which  the  class  of  aldehydes  derived  its 
name,  and  when  the  term  "aldehyde"  is  used  without  qualification 
acetic  aldehyde  is  understood. 

Aldehyde  results  from  the  destructive  distillation  of  various  organic 
compounds  and  from  the  limited  oxidation  of  alcohol,  as  by  dilute 
chromic  acid,  or  by  air  in  presence  of  platinum  black.  In  practice 
it  is  prepared  by  distilling  together  alcohol,  sulphuric  acid,  and  man- 
ganese dioxide. 

It  is  a  colourless,  mobile  liquid,  with  a  pungent,  suffocating  odor. 
The  disagreeable  odour  is  much  stronger  in  the  crude  substance.  Its 
sp.  gr.  is  0.790  and  it  boils  at  22°.  It  does  not  redden  litmus,  but  on 
exposure  to  air,  oxidises  slightly  to  acetic  acid. 

Acetic  aldehyde  is  miscible  in  all  proportions  with  water,  alcohol, 
and  ether.  It  is  insoluble  in  a  saturated  solution  of  calcium  chloride, 
but  this  property  is  not  available  for  the  quantitative  separation  of  al- 
dehyde from  alcohol.  A  better  method  is  to  treat  the  liquid  with  dry 
calcium  chloride,  which  forms  a  compound  with  the  alcohol,  when  the 
aldehyde  may  be  distilled  off  by  the  heat  of  a  water-bath. 

When  kept  in  closed  vessels,  aldehyde  often  passes  into  liquid  or  solid 
polymers,  especially  in  presence  of  traces  of  mineral  acid.  An  alcoholic 
solution  is  tolerably  permanent.  Dehydrolyzing  agents,  such  as  phos- 
phoric anhydride  and  concentrated  sulphuric  acid,  when  heated  with 


ALDEHYDE.  265 

aldehyde  turn  it  thick  and  black,  but  it  may  be  distilled  from  sulphuric 
acid  diluted  with  an  equal  weight  of  water. 

Aldehyde  is  a  powerful  reducing  agent.  It  separates  metallic  silver 
from  the  ammonionitrate,  when  gently  warmed,  an  acetate  being 
formed  in  the  liquid.  The  reaction  is  rendered  more  delicate  by  the 
addition  of  alkali.  A  suitable  mixture  may  be  prepared  by  mixing 
equal  measures  of  10%  aqueous  solutions  of  silver  nitrate  and 
sodium  hydroxide,  and  then  adding  ammonia  drop  by  drop  till  the 
oxide  of  silver  is  dissolved.  The  reagent  shauld  be  freshly  prepared,  as 
it  is  liable  to  decompose  with  deposition  of  fulminating  silver.  It 
yields  an  immediate  mirror  with  a  liquid  containing  i%  of  alde- 
hyde, and  in  half  a  minute  with  a  solution  containing  i  in  1000,  while 
i  part  of  aldehyde  in  10,000  of  water  yields  a  yellow-brown  mirror  in 
five  minutes.  The  solution  to  be  tested  should  be  previously  dis- 
tilled, as  several  varieties  of  sugar  slowly  reduce  the  reagent. 

Aldehyde  gives  a  copious  precipitate  of  cuprous  oxide  when  heated 
with  Fehling's  solution. 

When  in  alcoholic  or  aqueous  solution,  aldehyde  is  conveniently 
detected  by  its  reaction  on  heating  with  sodium  hydroxide.  When 
thus  treated,  the  liquid  becomes  yellow  and  turbid,  and  a  reddish-brown 
resinous  mass  rises  to  the  surface,  the  liquid  emitting  a  highly  dis- 
agreeable odour.  The  solution  contains  formate  and  acetate.  This 
formation  of  aldehyde-resin  is  the  characteristic  reaction  of  aldehyde, 
and  has  been  utilised  by  J.  C.  Thresh  (Pharm.  Jour.,  [3],  1878,  9, 
409,  9  (1878-9),  409),  for  its  estimation.  To  effect  this,  i  part  of 
pure  aldehyde  should  be  diluted  with  200  measures  of  water,  30 
measures  of  a  syrupy  solution  of  sodium  hydroxide  added,  and  the 
whole  heated  and  kept  at  the  b.  p.  for  a  few  seconds.  It  is  then 
allowed  to  cool,  and  after  two  hours  is  diluted  with  200  measures 
of  warm  methylated  spirit  (free  from  aldehyde),  and  then  made  up  to 
500  measures  by  addition  of  water.  This  solution  is  quite  clear,  and 
of  a  reddish-yellow  color.  As  it  quickly  alters,  it  is  desirable  to  make 
a  solution  of  potassium  bichromate  of  the  same  tint,  and  employ  that 
instead  of  the  original  liquid.  To  determine  aldehyde,  the  liquid  con- 
taining it,  suitably  diluted  and  previously  distilled  if  necessary,  is 
treated  in  exactly  the  same  manner  as  the  pure  aldehyde,  and  the 
colour  of  the  liquid  obtained  compared  with  the  standard,  and  the 
darker  diluted  with  water  till  the  tints  are  identical.  The  comparison 
is  effected  in  much  the  same  manner  as  in  Nessler's  test. 


266  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

Rocques'  Method  of  Estimating  Aldehyde  (/.  Pharm.  Chim. 
[6],  1898,  8,  390,  497). — An  alcoholic  sulphite  solution  is  prepared  by 
dissolving  12.6  grm.  sodium  sulphite  in  400  c.c.  of  water,  adding 
100  c.c.  of  N/ 1  sulphuric  acid,  and  making  to  1000  c.c.  with  95  %  alcohol 
of  the  highest  purity.  The  solution  is  allowed  to  stand  overnight 
and  filtered  from  the  sodium  sulphate. 

A  suitable  volume  of  the  sample,  which  should  not  contain  more 
than  2%  of  aldehyde,  is  placed  in  a  flask  marked  at  100  c.c.,  an 
accurately  measured  volume  of  the  alcoholic  sulphite  solution  is  added, 
and  the  liquid  is  made  up  to  100  c.c.  with  50%  alcohol  of  highest 
purity.  The  flask  should  have  a  long  neck  and  be  well  closed  after 
the  mixture  is  made  up.  A  similar  flask  is  prepared  with  the  diluted 
reagent  alone.  The  flasks  are  kept  at  50°  for  four  hours,  cooled,  and 
the  contents  titrated  with  standard  iodine  with  starch  in  the  usual 
manner.  Rocques  uses  different  strengths  of  iodine  according  to  the 
amount  of  aldehyde  present,  but  for  ordinary  cases  he  prescribes  N/ 1 
solution.  If  the  sulphite  solution  has  been  properly  made,  it  and  the 
iodine  solution  will  be  equivalent  volume  for  volume,  i  c.c.  of  N/ 1 
iodine  equals  0.0032  of  sulphur  dioxide  or  0.0022  of  acetic  aldehyde. 

For  a  method  of  preparing  a  standard  aldehyde  solution  and  for 
further  information  in  reference  to  estimation  of  aldehyde,  see  p.  198. 

Aldehyde  also  combines  with  ammonia  (NH3)  forming  a  crystalline 
substance  of  the  formula  C2H4O,NH3,  or  CH3.CH(NH2).OH  (amido- 
ethyl  alcohol),  insoluble  in  ether  and  decomposed  on  distillation  with 
moderately  dilute  sulphuric  acid. 

For  a  special  process  for  separating  formaldehyde  and  acetaldehyde, 
see  page  264. 

Betanaphthol  test  (Mulliken,  I  dent.  Pure  Org.  Comp.,  vol.  i), 
about  0.25  grm.  betanaphthol,  2  drops  hydrochloric  acid  and  20  c.c. 
glacial  acetic  acid  are  shaken  until  the  naphthol  is  all  dissolved.  A 
drop  of  the  solution  to  be  tested  is  then  added  and  the  liquid  heated 
to  between  50°  and  60°  for  5  minutes,  boiled  for  i  minute,  cooled  and 
shaken  vigourously  until  a  precipitate  settles.  As  the  liquid  tends  to 
show  the  phenomenon  of  supersaturation,  it  will  be  well  to  allow 
considerable  time  and  to  stir  actively  with  a  glass  rod  before  deciding 
that  the  result  is  negative.  If  a  precipitate  appears,  it  should  be  col- 
lected on  a  filter  previously  moistened  with  glacial  acetic  acid,  washed 
with  i  c.c.  of  the  same,  then  boiled  with  a  mixture  of  3  c.c.  alcohol  and 
t  c.c.  water  for  half  a  minute.  Much  of  the  precipitate  may  not  dis- 


ALDEHYDE  267 

solve.  The  solution  is  cooled  thoroughly,  shaken  actively,  and  the 
precipitate  that  separates  collected  on  a  filter,  washed  with  i  c.c.  cold 
dilute  alcohol  (i  to  i)  and  dried  for  30  minutes  at  100°.  If  acetic  alde- 
hyde was  present  in  the  liquid  tested,  the  product  is  ethylidene-dibeta- 
naphthol  oxide  (C10H6),O(C2H4),  which  melts  at  172.5°  to  173.5°. 

Paraldehyde.  C6H12O3. — This  polymeride  is  produced  by  adding 
a  minute  quantity  of  hydrochloric  or  sulphurous  acid  to  ordinary  alde- 
hyde. Also,  on  adding  a  drop  of  concentrated  sulphuric  acid  to  alde- 
hyde violent  ebullition  occurs,  much  aldehyde  is  volatilised,  and  the 
residue  consists  of  paraldehyde.  Zinc  chloride  acts  similarly,  but 
calcium  chloride  and  potassium  acetate  do  not.  The  paraldehyde 
may  be  purified  from  unchanged  aldehyde  by  cooling  the  liquid  below 
o°,  when  the  crystals  which  separate  are  pressed  between  folds  of  blot- 
ting-paper and  distilled. 

Paraldehyde  is  a  colourless,  transparent  liquid  with  strong  odour  and 
sharp  taste.  Its  sp.  gr.  is  0.990  at  25°  (United  States  Pharmacopoeia). 
It  is  soluble  in  8  parts  of  cold  and  16.5  parts  of  boiling  water;  on  ac- 
count of  the  lower  solubility  at  the  higher  temperature,  the  cold  satu- 
rated solution  becomes  turbid  on  boiling.  Paraldehyde  is  miscible  in 
all  proportions  with  alcohol  and  ether.  It  solidifies  at  about  o°,  melts 
at  1 0.5°  and  boils  at  between  121°  and  125°.  The  vapour  is  inflammable. 
The  liquid  is  nominally  neutral,  but  maybe  slightly  acid  to  litmus.  It 
possesses  reducing  power  similar  to  ordinary  aldehyde.  The  United 
States  Pharmacopoeia  requires  that  i  c.c.  of  paraldehyde  shall  form 
with  10  c.c.  of  water  a  clear  solution,  which  must  not  precipitate  with 
silver  nitrate  or  barium  chloride. 

Metaldehyde,  #C2H4O,  is  another  polymeride  produced  simul- 
taneously with  paraldehyde  (see  above).  It  is  insoluble  in  water, 
and  almost  insoluble  in  alcohol  or  ether,  but  dissolves  somewhat  in 
acetaldehyde.  Its  best  solvents  are  hot  chloroform  and  benzene.  At 
ordinary  temperatures  the  crystals  are  permanent  in  the  air.  It  is 
reconverted  more  or  less  completely  into  ordinary  aldehyde  by  re- 
peated distillation  or  by  heating  in  a  sealed  tube  to  110°  or  115°  and 
readily  by  distillation  with  a  little  dilute  sulphuric  acid.  Permangan- 
ates, chromic  acid  mixture,  and  ammonium  hydroxide  are  without  effect 
on  metaldehyde,  but  chlorine  at  once  converts  it  into  ordinary  chloral. 
With  a  hot  strong  solution  of  alkali,  metaldehyde  very  slowly  yields 
aldehyde-resin,  the  reaction  being  probably  preceded  by  a  formation 
of  ordinary  aldehyde. 


268  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

Acetal,  C6H14O2,  has  the  constitution  of  a  di-oxyethyl-acetaldehyde : 
CH3.CH(OC2H5)2.  It  is  produced  by  the  action  of  aldehyde  on 
alcohol,  and  hence  is  a  constituent  of  crude  spirit  and  of  the  "feints" 
obtained  in  the  rectification  of  alcohol.  When  pure,  acetal  is  a  liquid 
of  pleasant  taste  and  odour,  boiling  at  about  105°  and  having  a  density 
of  0.821  at  22°.  By  oxidising  agents  it  is  converted  into  acetic  acid  and 
aldehyde,  and  when  heated  with  acetic  acid,  it  yields  ethyl  acetate 
and  aldehyde.  If  a  dilute  aqueous  solution  be  treated  with  sodium 
hydroxide  and  iodine  a  clear  colourless  liquid  is  formed,  which  yields 
a  dense  precipitate  of  iodoform  when  acidified.  From  alcohol,  acetal 
may  be  separated  by  distillation  over  dry  calcium  chloride  and  from 
aldehyde  and  ethyl  acetate  by  heating  the  liquid  with  strong  solution 
of  potassium  hydroxide. 

Dimethyl-acetal  occurs  in  crude  wood  spirit  in  proportions  ranging 
from  i  to  2%. 

CHLORAL. 

Trichloraldehyde.     C2HC13O. 

Chloral  is  obtained  in  practice  by  the  prolonged  action  of  dry  chlorine 
on  absolute  alcohol.  When  the  liquid  acquires  a  sp.  gr.  of  1.400 
it  is  distilled  with  an  equal  weight  of  strong  sulphuric  acid,  the  fractions 
passing  over  below  94°  being  kept  separate,  and  the  process  stopped 
when  the  temperature  rises  to  100°.  The  distillate  is  neutralised  with 
calcium  carbonate  and  again  distilled.  The  reactions  which  occur 
in  the  manufacture  of  chloral  are  very  complicated,  and  secondary 
products  are  liable  to  be  formed. 

Chloral  is  a  colourless  oily  liquid,  sp.  gr.  1.544  at  0°,  or  1.502  at 
1 8°.  It  boils  at  94.4°  and  distils  unaltered.  It  is  soluble  in  ether  or 
chloroform  without  change. 

When  kept  for  some  time,  or  when  left  in  contact  with  moderately 
concentrated  sulphuric  acid,  chloral  is  converted  into  an  insoluble  poly- 
meric modification  called  metachloral,  which  is  insoluble  in  cold 
and  but  sparingly  soluble  in  boiling  water  and  insoluble  in  alcohol 
or  ether  even  when  boiling.  Pure  chloral  does  not  become  poly- 
merised, and  the  change  is  also  said  to  be  prevented  by  addition  of  a 
little  chloroform.  When  heated  to  180°  metachloral  distils  with  re- 
version to  liquid  chloral.  By  the  action  of  alkalies  chloral  yields  chloro- 
form and  a  formate. 


CHLORAL.  269 

If  an  aqueous  solution  of  chloral  is  heated  to  50°  with  zinc,  and 
very  dilute  acid  gradually  added,  aldehyde  and  paraldehyde  are  formed 
and  may  be  distilled  off. 

When  chloral  is  mixed  with  an  equivalent  quantity  of  absolute  al- 
cohol it  is  converted  into — 

Chloral  Alcoholate. 

This  substance  forms  white  crystals,  which  melt  at  46°.  It  boils 
at  113.5°.  These  properties  serve  among  others,  to  distinguish  it 
from — 

Chloral  Hydrate.  Trichlorethylidene  glycol.  This  substance  re- 
sults from  the  mixture  of  equivalent  quantities  of  chloral  and  water. 
The  mixture  becomes  heated  and  solidifies  to  a  mass  of  crystals. 
The  term  " chloral  hydrate"  is  a  misnomer;  the  substance  is  not  a 
combination  of  water  and  chloral,  but  a  chlorinated  diatomic  alcohol. 
The  term  is,  however,  too  firmly  fixed  in  medical  and  pharmaceutic 
literature  to  be  avoided,  and  hence  it  will  be  used  in  this  work. 

Chloral  hydrate  is  soluble  in  1.5  times  its  weight  of  water  and  is 
also  soluble  in  alcohol,  ether,  benzene,  petroleum  spirit,  and  carbon 
disulphide.  When  crystallised  from  the  last  solution  it  boils  at  97.5°. 
When  mixed  with  an  equal  weight  of  camphor  or  phenol  it  rapidly 
liquefies.  The  liquid  has  the  mixed  odour  of  its  constituents  and 
does  not  precipitate  silver  nitrate. 

Chloral  hydrate  is  soluble  with  difficulty  in  cold  chloroform,  requir- 
ing four  times  its  weight;  a  fact  which  distinguishes  it  from  the  alcohol- 
ate,  which  is  readily  soluble  in  chloroform.  The  alcoholate  repre- 
sents less  chloral  than  the  hydrate. 

Chloral  hydrate  and  alcoholate  should  be  completely  volatile  and 
their  aqueous  solutions  should  be  perfectly  neutral  to  litmus. 

Aqueous  solution  of  chloral  hydrate  gives  no  reaction  with  silver 
nitrate  in  the  cold,  but  on  boiling  and  adding  a  little  of  ammonium 
hydroxide  a  mirror  is  readily  produced.  If  kept  some  time,  chloral 
hydrate  contains  a  trace  of  hydrochloric  acid,  and  the  solution  in 
water  then  gives  a  cloud  with  silver  nitrate,  but  the  production  of  a 
distinct  precipitate  indicates  serious  impurity. 

When  water  is  present  chloral  hydrate  is  deliquescent,  and  in 
warm  weather  even  melts.  Hence  it  is  often  made  with  a  slight  de- 
ficiency of  water.  If  more  than  a  shade  short  of  this  the  product  has 
a  tendency  to  become  acid,  and  ultimately  partially  insoluble  from  for- 
mation of  metachloral. 


270 


NEUTRAL    ALCOHOLIC    DERIVATIVES. 


In  the  following  table  are  given  other  useful  distinctions  between 
chloral  alcoholate  and  chloral  hydrate : 


Chloral  alcoholate 


Chloral  hyirate 


1.  M.  P. 

2.  B.  P. 

3.  Sp.  gr.  of  the  fused    substance 

at  66°: 

4.  Sp.  gr.  of  the  aqueous  solution 

at  15.5°: 

5% 
10  " 

2- 

5.  Gently  heated  with  nitric  acid 

of  1.2  sp.  gi. 

6.  Shaken  with  an  equal  volume 

of  strong  sulphuric  acid. 

7.  Warmed  with  two  volumes  of 

water. 


8.  Heated  on  platinum  foil. 

9.  With  alkali  and  iodine. 


46° 

113-5° 
1-344 


i  .007 
1.028 
i  .050 
i  .071 
Violently  attacked. 

Brown. 

Melts  without  com- 
plete solution,  and 
on  cooling  congeals 
below  the  surface. 

Inflames  readily. 

Gives  iodoform. 


48°-49c 
97-5° 


i  .019 
i  .040 
i  .062 
1.085 
Scarcely  acted  on. 

No  visible  change. 
Readily  dissolved. 


Scarcely  burns. 
Gives  no  iodoform. 


The  solidifying  point  of  melted  chloral  hydrate  is  an  indication  of 
some  value.  The  sample  should  be  placed  in  a  small  test-tube,  fused, 
and  the  tube  immersed  in  water  at  about  55°.  A  thermometer  is 
placed  in  the  liquid,  and  the  temperature  at  which  it  becomes  opales- 
cent noted.  The  best  quality  solidifies  at  about  48°  to  49°,  and  the  best 
practically  adjusted  specimens  within  half  a  degree  of  50°.  A  low 
freezing  point  indicates  excess  of  water,  and  such  specimens  are  liable 
to  deliquesce.  Small  granular  crystals  and  saccharoid  masses  are  purer 
than  large  crystals  or  needles. 

The  b.  p.  is  also  of  service  as  a  test  of  purity.  The  sample  should 
be  placed  in  a  test-tube  with  some  broken  glass.  A  pure  sample 
will  begin  to  boil  rapidly,  97°,  and  the  temperature  will  change  but 
little  until  one-half  has  been  volatilised.  The  material,  however,  under- 
goes slow  decomposition  at  the  b.  p.,  so  that  the  first  portions  of  the  dis- 
tillate are  underhydrated,  and  the  last  overhydrated.  The  b.  p. 
consequently  undergoes  a  gradual  rise.  The  best  commercial  speci- 
mens, i.  e.,  those  slightly  underhydrated,  begin  to  boil  throughout  the 
liquid  at  about  965°.  The  underhydrated  portion  boils  off  in  a  few 


CHLORAL  HYDRATE.  271 

seconds,  and  the  b.  p.  rises  to  97°,  and  finally  to  97.5°  or  98°,  by  the 
time  half  has  boiled  away.  A  b.  p.  above  98°  indicates  an  over- 
hydrated  and  deliquescent  sample.  If  the  boiling  fairly  commences 
below  95°,  the  sample  is  too  much  underhydrated,  and  is  liable  to 
decompose  on  keeping. 

Detection  and  Estimation  of  Chloral. — The  detection  and 
estimation  of  chloral  have  acquired  considerable  importance  of 
recent  years  on  account  of  the  not  infrequent  employment  of  the  sub- 
stance for  drugging  liquor  to  facilitate  the  commission  of  robbery  or 
rape. 

Chloral  hydrate  may  be  detected  by  the  same  means  as  chloroform 
(page  274).  It  reduces  Fehling's  solution  on  heating.  The  reaction 
may  be  employed  to  detect  traces  of  chloral  if  other  reducing  sub- 
stances are  absent,  and  might  probably  be  made  quantitative. 

Traces  of  chloral  may  be  detected  by  Hofmann's  test  for  chloroform 
(see  page  2  74) ;  also,  by  boiling  the  liquid  and  passing  the  vapour  through 
a  red-hot  tube,  when  hydrochloric  acid  will  be  formed,  and  the  con- 
densed water  will  precipitate  silver  nitrate. 

For  the  estimation  of  real  chloral  yielded  by  the  hydrate,  advan- 
may  be  taken  of  the  reaction  with  alkalies,  which  results  in  the 
separation  of  chloroform  and  the  production  of  a  formate. 

K.  Miiller  gives  the  following  method:  25  grm.  of  the  sample 
are  placed  in  a  finely-graduated  tube,  and  a  strong  solution  of  po- 
tassium hydrate  added,  in  quantity  rather  more  than  sufficient  for 
the  above  reaction.  A  large  excess  must  be  avoided.  The  tube 
must  be  kept  well  cooled,  as  the  action  is  very  violent  at  first.  After- 
wards, the  tube  may  be  closed  and  the  mixture  shaken.  After  resting 
an  hour  or  two  the  liquid  becomes  clear  and  separates  into  two  layers. 
The  lower  layer  is  chloroform,  and,  after  being  brought  to  a  tempera- 
ture of  17°,  the  volume  may  be  read  off.  Its  sp.  gr.  is  1.491,  and  hence 
the  measure  of  chloroform  in  c.c.,  multiplied  by  1.84,  gives  the  grms. 
of  anhydrous  chloral  in  the  quantity  of  the  sample  employed.  If  the 
factor  2.064  be  substituted,  the  product  will  be  the  weight  of  chloral  hy- 
drate present.  Miiller  obtained  by  this  process  an  average  of  71.6  % 
of  chloroform  from  pure  chloral  hydrate,  against  72.2  %  as  required 
by  theory. 

C.  H.  Wood  proposed  the  following:  10  grm.  of  the  sample  are 
dissolved  in  50  c.c.  of  water  contained  in  a  small  flask,  and  4  grm.  of 
slaked  lime  is  added.  A  cork  with  a  tube  bent  twice  at  right  angles  is 


272  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

adapted  to  the  flask,  the  outer  end  of  the  tube  being  somewhat  drawn  out 
and  immersed  in  a  small  quantity  of  water,  contained  in  a  narrow  grad- 
uated glass  tube  surrounded  with  cold  water.  A  gentle  heat  is  applied 
to  the  flask,  and  the  chloroform  slowly  distilled  over.  After  a  few 
minutes  the  heat  is  gradually  increased,  so  as  to  keep  the  mixture  boil- 
ing, the  operation  being  continued  till  10  c.c.  measure  has  passed  over. 
Nothing  remains  but  to  bring  the  chloroform  to  the  proper  temperature 
and  read  off  the  volume.  The  addition  of  a  few  drops  of  potassium- 
hydroxide  solution  destroys  the  meniscus  of  the  chloroform,  and  en- 
ables the  operator  to  observe  the  measure  accurately.  The  process 
is  brief.  Too  much  lime  occasions  frothing,  but  an  excess  appears 
to  have  no  decomposing  action  on  the  chloroform.  Lieben's  iodoform 
test  for  alcoholate  is  readily  applied  to  the  aqueous  portion  of  the  dis- 
tillate. Allen  found  this  plan  convenient  and  fairly  accurate.  A  correc- 
tion may  advantageously  be  made  for  the  slight  solubility  of  chloroform. 
This  is  about  0.3  c.c.  for  every  100  c.c.  of  aqueous  liquid. 

A  simple  and  satisfactory  modification  of  the  process  has  been 
suggested  by  M.  Meyer,  and  has  given  satisfactory  results.  It  has 
the  advantage  of  being  applicable  to  small  amounts  of  material.  One 
or  2  grms.  of  the  sample  are  dissolved  in  water,  and  free  acid  removed 
by  shaking  the  liquid  with  barium  carbonate  and  filtering.  The 
filtrate  is  treated  with  a  moderate  excess  of  normal  sodium  hy- 
droxide, and  titrated  back  with  acid  in  the  usual  way,  litmus  being 
used  as  an  indicator.  Each  c.c.  of  normal  alkali  neutralised  by  the 
sample  corresponds  to  0.1475  grm-  °f  chloral  (C2HC13O),  or  0.1655 
grm.  of  chloral  hydrate. 

Other  processes  of  assaying  chloral  hydrate  have  been  based  on  its 
decomposition  by  ammonium  hydroxide  and  on  its  conversion 
into  chloral  by  sulphuric  acid,  but  they  are  liable  to  error,  and  are  not 
better  than  the  methods  described. 

Trichloracetic  acid. — This  is  a  product  of  the  action  of  oxi- 
dising agents  on  chloral.  When  equivalent  quantities  of  chloral 
hydrate  and  potassium  permanganate  are  cautiously  mixed  in  concen- 
trated solution,  potassium  trichloracetate  is  formed,  and  may  be 
obtained  in  white  silky  crystals  by  filtering  and  evaporating  the  liquid. 
By  the  action  of  alkalies,  trichloracetic  acid  yields  chloroform  and  a 
carbonate,  and  responds  to  all  other  tests  for  chloral  dependent  on  its 
conversion  into  chloroform. 

The  acid  may  be  obtained  by  decomposing  the  potassium  salts  in  the 


BUTYL    CHLORAL.  273 

usual  way.  It  forms  colourless  crystals,  very  deliquescent.  The  solu- 
tion is  powerfully  acid  and  corrosive.  It  coagulates  albumin  and  is 
one  of  the  most  delicate  tests  for  this  substance.  Assay  of  the  acid 
may  be  made  by  titrating  standard  alkali  and  applying  the  methods 
used  in  assaying  chloral  hydrate. 

Butyric  Chloral.  Butyl  Chloral. — Butyric  trichloraldehyde. 
This  is  erroneously  called  croton  chloral.  When  chlorine  is  passed 
into  aldehyde,  this  substance  is  formed  in  addition  to  ordinary 
chloral.  It  bears  the  same  relation  to  butyl  alcohol  and  butyric  acid 
that  ordinary  chloral  bears  to  ethyl  alcohol  and  acetic  acid. 

Butyl  chloral  was  at  first  called  croton  chloral,  the  hydrogen  being 
underestimated,  which  led  to  the  supposition  that  it  was  the  trichlorin- 
ated  aldehyde  of  crotonic  acid,  the  fourth  member  of  the  acrylic  or 
oleic  acid  series. 

Butyric  chloral  is  a  dense,  oily  liquid  of  peculiar  odour,  boiling  at 
about  163°.  When  treated  with  a  considerable  excess  of  warm  water 
it  dissolves,  and  on  cooling  deposits 

Butyric  Chloral  Hydrate. 

This  substance  forms  white,  silvery  crystalline  scales  melting  at  78° 
and  having  a  sweetish  melon  flavour.  The  sp.  gr.  is  1.695, tnat  °f  son^l 
chloral  hydrate  being  i  .8 18.  Butyric  chloral  hydrate  is  but  little  soluble 
in  cold  water,  but  more  so  in  hot.  Its  solubility  is  increased  by  addition 
of  glycerol.  It  is  very  soluble  in  alcohol  and  ether,  but  insoluble,  or 
nearly  so,  in  chloroform.  This  last  property  may  be  employed  to 
separate  it  approximately  from  ordinary  chloral  hydrate.  It  differs 
also  from  the  latter  body  in  its  m.  p.  and  b.  p.  The  two  bodies  may  also 
be  separated  by  distillation,  ordinary  chloral  hydrate  passing  over  a 
little  below  100°,  while  butyric  chloral  hydrate  is  decomposed  into 
water,  which  distils  at  about  100°,  and  anhydrous  butyric  chloral 
boiling  at  about  163°. 

When  acted  on  by  alkalies,  butyric  chloral  hydrate  is  at  first  decom- 
posed with  production  of  a  formate  and  propylic  chloroform,  but  this 
again  splits  up  with  formation  of  a  metallic  chloride  and  allylene 
dichloride. 

Allylene  dichloride  is  very  unstable,  being  gradually  decomposed 
even  at  ordinary  temperatures,  and  acquiring  an  acid  reaction  and 
disagreeable  odour.  The  proneness  to  change,  so  marked  in  some 
samples  of  commercial  chloroform,  and  the  readiness  with  which  the 
latter  decomposes  and  becomes  acid,  are  properties  possibly  due  to 
VOL.  T— 18 


274  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

the  presence  of  allylene  dichloride.  Its  presence  may  be  due  to  the 
existence  of  aldehyde  in  the  crude  alcohol  used  for  the  preparation  of 
the  chloroform.  By  the  action  of  chlorine  the  aldehyde  is  converted 
into  butyl  chloral,  and  this,  by  subsequent  contact  with  the  calcium 
carbonate  used  for  neutralisation,  gives  allylene  dichloride. 

Chloralformamide. 

This  is  produced  by  the  action  of  formamide  (CH3NO)  on  chloral. 
It  forms  colourless,  odourless  crystals,  soluble  in  about  19  parts  of 
water  at  25°.  The  solution  is  somewhat  bitter  and  is  neutral  to 
litmus.  One  part  of  chloral-formamide  dissolves  in  1.3  parts  of 
alcohol,  and  it  is  also  readily  soluble  in  ether,  glycerol,  ethyl  acetate, 
and  acetone.  Heated  alone,  it  melts  at  about  115°  and  at  a  higher 
temperature  volatilises  leaving  no  appreciable  residue.  Its  solution  in 
water  is  not  affected  by  acids,  but  is  decomposed  by  sodium  hydroxide 
with  formation  of  chloroform.  The  solution  in  alcohol  does  not  redden 
litmus  nor  produce  a  precipitate  with  solution  of  silver  nitrate. 

CHLOROFORM. 

Trichlormethane.    Methylene  terchloride. 

Chloroform  was  formerly  made  by  distilling  dilute  alcohol  with 
calcium  hypochlorite  and  calcium  hydroxide,  but  it  is  now  prepared 
largely  from  acetone  and  from  chloral. 

Chloroform  is  a  colourless  liquid  of  marked  odour  and  sharp,  sweetish 
taste.  It  is  very  volatile.  The  vapour  is  not  combustible  alone,  but 
in  mixture  with  alcohol  vapour,  burns  with  a  smoky  flame,  edged  with 
green.  According  to  Landolt  and  Bornstein's  Tabellen,  chloroform 
has  a  sp.  gr.  1.5264  at  o°/4°,  melts  at  70°  and  boils  at  61.2°  (corrected). 

Chloroform  is  soluble  in  about  200  volumes  of  cold  water  (0.44  grm. 
iniooc.c.),  to  which  it  imparts  a  sweet  taste.  It  is  miscible  in  all 
proportions  with  absolute  alcohol,  ether,  benzene,  and  petroleum 
spirit.  It  is  soluble  to  a  limited  extent  in  dilute  alcohol.  It  dissolves 
many  organic  bases,  fats,  waxes,  resins,  camphor,  india-rubber,  gutta- 
percha,  iodine,  bromine,  and  phosphorus. 

Detection  and  Estimation  of  Chloroform. — As  a  rule,  the  de- 
tection of  chloroform  itself  is  less  important  than  the  recognition 
and  estimation  of  other  substances  in  presence  of  chloroform. 

A  very  delicate  method  for  the  detection  of  chloroform  in  presence 
of  large  quantities  of  alcohol  has  been  described  by  A.  W.  Hofmann. 


CHLOROFORM.  275 

All  that  is  necessary  is  to  add  some  alcoholic  sodium  hydroxide  and  a 
little  aniline  to  the  liquid  to  be  tested.  Either  immediately  or  on  gently 
warming  the  mixture,  a  strong  and  peculiar  smell  will  be  observed, 
due  to  the  formation  of  phenyl  carbamide  (phenyl  isocyanide), 
Bromoform  and  iodoform  give  the  same  reaction,  as  also  do  chloral, 
trichloracetic  acid,  and  all  other  bodies  which  yield  either  of  the  above 
products  by  treatment  with  alkalies,  but  ethylidene  chloride,  C2H4C12, 
gives  no  isonitrile  under  these  conditions.  The  test  is  so  delicate 
that  one  part  of  chloroform  dissolved  in  5,000  parts  of  alcohol  may  be 
detected  with  certainty  by  means  of  it. 

Reduction  of  Fehling's  solution  is  also  a  test  for  chloroform.  When 
the  solution  is  heated,  the  cuprous  oxide  separates  promptly.  Chlor- 
ethylidene  and  alcohol  do  not  interfere  with  the  test. 

When  chloroform  vapour  mixed  with  hydrogen  is  passed  through  a 
red-hot  tube,  is  it  decomposed  with  production  of  hydrochloric  acid. 
This  reaction  is  used  for  the  detection  and  estimation  of  chloroform. 
The  sample  should  be  boiled  in  a  small  flask  through  which  a  current 
of  hydrogen  is  allowed  to  pass.  The  mixed  hydrogen  and  chloroform 
vapour  are  then  caused  to  traverse  a  short  length  of  heated  combustion 
tube  containing  platinum  wire-gauze  or  loose  asbestos. 

The  products  are  passed  through  a  bulb-tube  containing  water, 
and  the  hydrochloric  acid  is  titrated  with  standard  alkali,  or  precipi- 
ated  with  silver  nitrate.  109.5  parts  of  hydrochloric  acid,  or  430.5 
of  silver  chloride  represent  119.5  °f  chloroform.  Berthelot  points 
out  that  the  reaction  with  silver  is  apt  to  be  vitiated  by  the  presence 
of  acetylene  and  hydrocyanic  acid,  and  recommends  that  the  aqueous 
solution  of  the  gases  should  be  well  boiled  before  adding  silver 
nitrate. 

This  process  is  especially  useful  for  the  estimation  of  small 
quantities  of  chloroform  contained  in  other  non-chlorinated  liquids. 
It  may  be  employed  for  the  detection  and  estimation  of  chloroform  in 
blood.  When  its  detection  only  is  required,  a  current  of  air  may  be 
substituted  for  the  hydrogen.  There  is  no  occasion  to  heat  the  blood. 

Vitali  suggests  that  the  mixture  of  hydrogen  with  chloroform  vapour 
obtained  as  in  the  last  reaction  should  be  submitted  to  Hofmann's 
isonitrile  reaction  or  passed  through  a  freshly  prepared  mixture 
of  thymol  and  solid  potassium  hydroxide,  when  if  chloroform  is  present 
the  mixture  will  be  coloured  a  fine  reddish-violet. 

When  chloroform  is  added  to  a  solution  of  a-  or  /3-naphthol  in  strong 


276  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

potassium  hydroxide,  and  the  liquid  is  heated  to  about  50°,  a  fine  blue 
is  developed,  changing  in  contact  with  the  air  to  blue-green,  green, 
green-brown,  and  finally  brown. 

Commercial  Chloroform. — The  United  States  Pharmacopoeia 
preparation  consists  of  "99  to  99.4  %,  by  weight,  of  absolute  chloro- 
form and  0.6  to  i  %  of  alcohol." 

Many  specimens  of  commercial  chloroform  undergo  more  or  less 
change  on  keeping.  According  to  Personne,  samples  liable  to  altera- 
tion contain  chloro-carbonic  ether,  C2H5CO2C1.  The  change  has 
also  been  attributed  to  the  presence  of  allylene  dichloride.  Specimens 
of  chloroform,  originally  of  good  quality,  become  on  keeping  impreg- 
nated with  hydrochloric,  hypochlorous,  and  formic  acids.  J.  Reg- 
nauld  has  found  that  carbon  oxychloride,  COC12,  was  readily  pro- 
duced by  the  action  of  ozonised  air  on  chloroform,  and  considers  the 
accidental  presence  of  this  body  in  chloroform  very  common.  He 
has  also  found  that  very  carefully  prepared  chloroform  can  be  kept  un- 
changed if  exposed  to  air  or  light  simply,  but  that  the  combined  action 
of  air  and  light  rapidly  affects  the  purity  of  the  preparation.  The 
change  is  entirely  prevented  by  the  addition  of  a  little  alcohol. 

In  addition  to  the  impurities  resultant  from  decomposition  by  keep- 
ing, commercial  chloroform  may  contain  alcohol,  aldehyde,  and 
various  chlorinated  bodies.  These  last  are  very  injurious  and  even  poi- 
sonous, and  are  detected  and  eliminated  with  considerable  difficulty. 
Other  products  may  be  present  if  the  alcohol  employed  for  the  manu- 
facture of  the  chloroform  contained  methyl  or  amyl  compounds.  Al- 
cohol and  aldehyde  are  sometimes  added  to  chloroform  in  very  consid- 
erable proportions.  The  adulteration  of  chloroform  with  ether  and 
acetic  ether  has  also  been  practised. 

Free  chlorine  and  hypochlorous  and  hydrochloric  acids  in 
chloroform  may  be  recognised  by  shaking  the  sample  with  a  solution  of 
silver  nitrate  which  in  presence  of  either  of  the  above  impurities  will 
produce  a  white  precipitate,  whereas  chloroform  itself  gives  no  reaction 
with  silver  nitrate,  either  in  aqueous  or  alcoholic  solution.  If  the  pre- 
cipitate blacken  on  heating  the  presence  of  aldehyde  or  formic  acid  is 
indicated.  Free  chlorine  and  hypochlorous  acid  are  distinguished  from 
hydrochloric  acid  by  their  power  of  bleaching  instead  of  merely  redden- 
ing litmus,  and  by  liberating  iodine  from  a  solution  of  pure  potassium 
iodide  when  the  sample  is  shaken  with  it.  The  liberated  iodine  colours 
the  chloroform  reddish-violet. 


CHLOROFORM.  277 

Ethylene  dichloride,  C2H4C12,  may  be  detected  by  drying  the  sample 
by  agitation  with  dry  potassium  carbonate  and  then  adding  potassium. 
This  does  not  act  on  pure  chloroform,  but  ethylene  dichloride  produces 
•chlorethylene,  C,H3C1,  a  gas  of  an  alliaceous  odour.  It  is  doubtful 
if  the  substance  in  chloroform  of  the  formula  C2H4C12  is  always  ethylene 
dichloride.  It  may  be  the  isomer,  ethylidene  chloride,  CH3.CHC12. 

The  presence  of  ethyl  chloride,  in  chloroform  is  best  recognised  by 
distilling  the  sample  with  water  in  a  water-bath.  The  first  portions 
of  the  distillate  will  have  a  distinct  smell  of  the  foreign  body. 

"Methylated  chloroform"  is  chloroform  prepared  from  wood 
spirit  or  methylated  spirit.  It  is  a  mistake  to  suppose  that  methylated 
chloroform  has  received  an  actual  addition  of  wood  spirit,  but  such 
chloroform  is  liable  to  be  much  less  pure  than  that  obtained  solely 
from  ethyl  alcohol. 

Imperfectly  purified  methylated  chloroform  is  specifically  lighter 
than  the  pure  substance,  has  an  empyreumatic  odour,  and  produces 
disagreeable  sensations  when  inhaled.  In  some  cases  such  chloroform 
seems  actually  poisonous  and  produces  general  and  rapid  prostration. 
Such  impure  chloroform  contains  a  notable  amount  of  a  chlorinated 
body,  lighter  than  water  and  boiling  at  a  much  higher  temperature 
than  chloroform.  A  similar  but  different  oil  (heavier  than  water)  is 
sometimes  contained  in  much  smaller  quantity  in  chloroform  prepared 
from  alcohol  containing  no  methyl  compounds. 

Owing  to  the  poisonous  actions  of  several  methyl  derivatives,  it  is 
inadvisable  to  use  for  medicinal  purposes  chloroform  made  from 
methylated  spirit. 

Chloroform  is  not  soluble  in  strong  sulphuric  acid  and,  when  pure, 
is  not  acted  on  until  after  the  lapse  of  some  time  when  shaken  with 
that  reagent.  Any  darkening  of  the  acid  which  occurs  may  be  due  to 
the  presence  of  aldehyde,  wood  spirit,  or  chlorinated  oils.  Pure  chloro- 
form floats  on  strong  sulphuric  acid  with  a  contact-surface  convex 
downwards,  but  if  impure  gives  a  plane  contact-surface.  The  United 
States  Pharmacopoeia  adds  the  following  to  this  test : 

2  c.c.  of  the  sulphuric  acid  separated  from  the  chloroform,  diluted 
with  5  c.c.  of  distilled  water,  should  remain  colourless  and  clear, 
and  while  hot  from  the  mixing,  should  be  odourless  or  give  but  a  faint 
vinous  or  ethereal  odour.  When  further  diluted  with  10  c.c.  of  distilled 
water,  the  liquid  should  remain  clear  and  should  not  be  affected  by 
silver-nitrate  solution. 


278  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

The  b.  p.  of  chloroform  is  a  valuable  indication  of  its  purity.  Chlo- 
roform boils  at  60.8°.  The  presence  of  1/2  %  of  alcohol  reduces  the 
b.  p.  to  59.8°  or  60°.  A  b.  p.  higher  than  61°  indicates  the  presence  of 
amyl  or  butyl  compounds.  In  some  cases  the  b.  p.  of  the  last  portions 
distilled  is  as  high  as  70°. 

Chloroform  volatilises  entirely  without  disagreeable  odour.  The 
impurities  are  generally  less  volatile.  Many  common  impurities  in 
chloroform  may  be  recognised  by  the  odour  left  on  the  evaporation  of 
the  sample  from  filter-paper  soaked  with  it. 

Chloroform  is  not  visibly  altered  when  heated  with  solution  of  potas- 
sium hydroxide,  but  it  is  slowly  acted  on  with  formation  of  formate  and 
chloride.  In  alcoholic  solution  this  reaction  occurs  rapidly. 

Any  considerable  admixture  of  ether  with  chloroform  would  be  indi- 
cated by  the  inflammability  and  diminished  density  of  the  liquid. 

Chloroform  does  not  change  the  colour  of  an  alkaline  solution  of 
potassium  permanganate  from  violet  to  green  within  half  a  minute, 
but  as  the  change  is  caused  by  alcohol  equally  with  more  objectionable 
impurities,  the  reaction  has  little  practical  value. 

The  most  delicate  test  for  the  presence  of  alcohol  in  chloroform  is 
that  of  A.  Lieben  as  modified  by  Hager.  The  sample  should  be  agi- 
tated with  five  measures  of  water,  the  liquid  passed  through  a  wet 
filter,  and  the  filtrate  examined  as  described  on  page  105. 

Potassium  hydroxide  is  quite  insoluble  in  dry  chloroform,  but  dis- 
solves sensibly  in  presence  of  water  or  alcohol.  A  little  of  the  solid  is 
fused  on  a  loop  of  platinum  wire  and  introduced  into  chloroform  con- 
tained in  a  dry  test-tube,  the  liquid  will  not  acquire  the  power  of 
turning  red  litmus-paper  blue  unless  water  or  alcohol  be  present.  If 
more  than  a  trace  of  alcohol  is  present,  the  decanted  chloroform,  when 
shaken  with  water,  yields  a  liquid  which  gives  a  blue  precipitate  with  a 
solution  of  copper  sulphate.  To  use  this  test  with  certainty  to  distin- 
guish between  water  and  alcohol  the  sample  must  be  first  shaken  with 
recently  ignited  potassium  carbonate.  This  treatment  will  remove 
water  but  not  alcohol,  so  that  if  the  chloroform  still  possesses  the  power 
of  dissolving  the  alkali  alcohol  is  present. 

Oudemanns  proposed  to  ascertain  the  alcohol  in  commercial  chloro- 
form by  shaking  10  c.c.  of  the  sample  in  a  flask  with  an  excess  of  pure 
dry  cinchonine.  The  flask  is  kept  for  an  hour  at  a  temperature  of  17°, 
with  frequent  agitation.  The  liquid  is  then  passed  through  a  dry  filter, 
and  5  c.c.  of  the  filtrate  evaporated  to  dryness  in  a  small  hand  beaker. 


CHLOROFORM. 


279 


The  following  are  the  amounts  yielded  by  5  c.c.  of  chloroform  con- 
taining different  proportions  of  alcohol : 


Residue 

Alcohol 

Residue 

Alcohol 

Mg. 

% 

Mg. 

% 

21 

0 

260 

6° 

6? 

i 

290 

7 

III 

2 

318 

8 

152 

3 

343 

9 

190 

4 

346 

10 

226 

5 

Stoedeler  has  suggested  f uchsine  for  detecting  alcohol  in  chloroform. 
The  sample  becomes  coloured  red  if  alcohol  is  present,  the  depth  of 
colour  varying  with  the  proportion  of  alcohol.  Allen  found  (Analyst, 
(1877,  22,  97)  that,  even  after  agitation  with  calcium  chloride,  chloro- 
form coloured  on  adding  fuchsine,  but  by  agitating  a  sample  with 
1/5  of  its  bulk  of  strong  sulphuric  acid,  and  subsequently  removing 
traces  of  the  latter  by  shaking  with  dry  precipitated  barium  carbonate, 
a  liquid  was  obtained  so  pure  as  to  give  only  a  very  slight  colouration. 
This  purified  chloroform  can  be  used  in  a  similar  manner  to  ether 
for  estimating  small  proportions  of  alcohol  in  chloroform.  Chloro- 
form may  also  be  purified  from  water,  alcohol,  and  ether  by  agitating 
with  sulphuric  acid  as  above,  separating  the  acid,  shaking  the  chlo- 
roform with  a  strong  solution  of  sodium  carbonate,  and,  lastly,  distilling 
it  over  freshly  burnt  lime. 

Chloroform  can  be  freed  from  water  and  alcohol  by  the  same 
processes  recommended  for  purifying  ether  (page  227).  The  reaction 
with  calcium  carbide  (page  no)  may  also  be  of  use. 

When  the  quantity  of  alcohol  in  chloroform  exceeds  i  or  2%,  the 
proportion  may  be  ascertained  with  tolerable  accuracy  by  shaking 
20  c.c.  of  the  sample  in  a  graduated  tube  with  80  c.c.  of  water.  If  the 
chloroform  is  pure  it  will  collect  at  the  bottom  in  clear  globules,  but  in 
the  presence  of  alcohol  the  liquid  and  the  surface  of  the  drops  will 
become  dim  and  opalescent.  The  reduction  in  the  volume  of  the 
chloroform  shows  the  proportion  of  alcohol  in  the  amount  taken. 
The  addition  of  a  few  drops  of  potassium  hydroxide  solution  destroys 
the  meniscus  and  enables  the  volume  to  be  read  more  accurately. 
The  aqueous  liquid  may  be  tested  for  sulphuric  acid  by  barium  chloride 


280  NEUTRAL   ALCOHOLIC    DERIVATIVES. 

for  free  Chlorine  or  hypochlorous  acid  by  starch  and  potassium  iodide ; 
for  hydrochloric  acid  by  silver  nitrate;  and  the  presence  of  alcohol 
definitely  proved  by  the  iodoform  test. 

The  proportion  of  alcohol  present  in  chloroform  can  in  some  cases 
be  ascertained  from  the  sp.  gr.  According  to  C.  Remys,  the  presence 
of  1/8  %  of  alcohol  reduces  the  sp.  gr.  by  .002,  and  1/2  %  by  .008. 
According  to  A.  H.  Mason,  chloroform  containing  i  %  of  alcohol  has  a 
sp.  gr.  of  1.497  at  I5-5°  C.  The  chloroform  of  the  British  Pharma- 
copoeia has  a  sp.  gr.  of  1.49.  Chloroform  containing  amyl  or  butyl 
compounds  has  a  higher  sp.  gr.  than  1.500. 

Chloroform  has  marked  antiseptic  powers  and  is  especially  con- 
venient for  preserving  urine  samples.  A  few  drops  well  shaken  with 
100  c.c.  will  be  sufficient  to  preserve  the  liquid  for  an  indefinite  time. 
An  excess  should  be  avoided,  as  the  globules  collect  at  the  bottom  of  the 
bottle  and  interfere  with  the  examination  of  the  sediment.  It  does  not 
simulate  the  common  tests  except  those  with  copper  solutions,  nor 
interfere  with  any  but  fermentation.  The  bismuth  and  phenylhydra- 
zine  tests  give  no  result  with  a  solution  of  chloroform  in  urine  free 
from  sugar.  Saccharine  urine  in  an  active  state  of  fermentation  is 
brought  to  quiescence  by  addition  of  chloroform.  The  liquid  may  be 
freed  from  the  preservative  by  adding  water  and  boiling  down  to  the 
original  volume. 

Spirit  of  chloroform,  British  Pharmacopoeia,  is  a  solution  of  chloro- 
form in  19  measures  of  rectified  spirit  (55°  O.  P.)  and  should  have  a 
density  of  0.871.  A  lower  sp.  gr.  may  be  due  to  deficiency  of  chloro- 
form or  to  the  use  of  spirit  of  60°  O.  P.  "  Chloric  ether"  is  a  spirituous 
solution  of  chloroform  of  uncertain  strength. 

Spirit  of  chloroform,  United  States  Pharmacopoeia,  consists  of  60  c.c. 
chloroform  and  940  c.c.  of  alcohol. 

The  proportion  of  chlorpform  present  in  spirit  of  chloroform,  "  chloric 
ether,"  and  similar  preparations  may  be  ascertained  with  accuracy  by 
introducing  into  a  narrow  graduated  tube  20  c.c.  of  the  sample  and 
30  c.c.  of  dilute  sulphuric  acid  (i  to  6)  coloured  with  a  little  fuchsine. 
A  cork  is  then  inserted  and  the  contents  of  the  tube  thoroughly  shaken. 
When  the  chloroform  has  separated,  the  tube  is  tapped  to  cause  any 
floating  globules  to  sink,  and  about  10  c.c.  of  petroleum  spirit  is  cau- 
tiously poured  on  the  surface  of  the  acid.  The  cork  is  reinserted  and 
the  volume  of  petroleum  spirit  employed  is  carefully  noted,  when  the 
contents  of  the  tube  are  well  mixed  by  agitation.  After  separation  the 


BROMOFORM.  281 

volume  of  petroleum  spirit  is  again  observed,  when  its  increase  will  be 
due  to  the  dissolved  chloroform.  Better  results  are  obtainable  in  this 
way  than  without  petroleum  spirit,  but  great  care  is  necessary  to  avoid 
error  from  expansion  or  contraction  through  alteration  of  temperature. 
Hence,  before  observing  the  volume  of  petroleum  spirit  originally  used, 
and  again  before  the  final  reading,  the  tube  should  be  immersed  in  a 
cylinder  of  cold  water  for  a  short  time.  The  process  gives  inaccurate 
results  when  the  proportion  of  chloroform  exceeds  about  30%.  In 
such  cases  the  method  given  on  page  275  should  be  employed. 

The  chloroform  in  mixtures  of  chloroform  and  alcohol  may  also  be 
determined  by  decomposition  with  alkali  in  the  manner  described  on 
page  278. 

Methylene  Dichloride.  Methene  Bichloride.  Dichlormethane. 
CH2C12. 

Methylene  dichloride  is  obtained  by  exposing  the  vapour  of  methyl 
chloride  in  admixture  with  chlorine  to  the  action  of  daylight  in  a 
large  glass  globe.  The  products  are  passed  through  two  Woulffe's 
bottles,  and  then  into  a  flask  surrounded  by  a  freezing  mixture. 
The  former  chiefly  retain  chloroform,  while  the  methylene 
dichloride  condenses  in  the  flask.  It  may  also  be  obtained  by 
the  reduction  of  chloroform  in  alcoholic  solution  by  zinc  and 
hydrochloric  acid. 

Methylene  dichloride  is  a  powerful  anaesthetic.  Being  more  expen- 
sive than  chloroform,  the  latter  liquid  is  sometimes  substituted  and  sold 
for  the  former,  which  it  closely  resembles  in  odour.  The  two  bodies 
may  be  distinguished  by  their  sp.  gr.  and  b.  p.  The  methylene  di- 
chloride burns  with  a  smoky  flame  and  dissolves  iodine  with  brown 
colour,  while  chloroform  unmixed  with  alcohol  burns  with  great  diffi- 
culty, giving  a  green-edged  flame,  and  dissolves  iodine  forming  reddish- 
violet  liquid. 

A  mixture  of  alcohol  and  chloroform  has  been  substituted  for 
methylene  dichloride.  On  shaking  the  sample  with  water,  the  alcohol 
would  be  dissolved,  and  the  chloroform  would  then  be  recognisable  by 
its  sp.  gr. 

Bromoform.     Tribromomethane. 

This  body  closely  resembles  chloroform,  but  boils  at  150°  to  152° 
Its  sp.  gr.  is  2.9  at  12°  or,  according  to  E.  Schmidt,  2.775  at  I4-5°- 
It  solidifies  at  +9°. 

Alkalies  convert  bromoform  into  chloride  and  formate.     By  the 


282  NEUTRAL    ALCOHOLIC    DERIVATIVES. 

action  of  alcoholic  potassium  hydroxide,  gas  is  evolved,  consisting  of 
one  volume  of  carbon  monoxide  and  three  of  ethylene. 

Bromoform  has  been  found  in  commercial  bromine,  (Hermann, 
Annalen,  1855).  It  may  be  detected  by  fractional  distillation  of  the 
bromine  on  the  water-bath  or  by  treating  the  sample  with  excess  of 
solution  of  potassium  iodide,  and  then  adding  sufficient  sodium 
thiosulphate  to  take  up  the  iodine  set  free.  The  characteristic  odour 
of  bromoform  then  becomes  apparent.  The  impurity  now  rarely, 
if  ever,  occurs. 

lodoform.     Triiodomethane. 

lodoform  is  produced  in  Lieben's  test  for  alcohol  (page  105).  It 
may  be  conveniently  prepared  by  heating  a  mixture  of  i  part  of  iodine, 
i  of  alcohol,  2  of  crystallised  sodium  carbonate,  and  10  of  water  to 
about  70  to  80°,  until  decolourised,  when  the  iodoform  separates  as 
lemon-yellow  powder,  which  may  be  filtered  from  the  liquid,  washed 
with  cold  water  and  dried. 

lodoform  is  a  light  yellow,  shining,  crystalline  solid,  having  a  per- 
sistent unpleasant  odour.  It  sublimes  at  a  gentle  heat  without  change, 
distils  with  vapour  of  water,  and  volatilises  sensibly  at  ordinary  tempera- 
tures. Heated  strongly,  it  is  decomposed  with  formation  of  violet 
vapours  of  iodine,  and  deposition  of  carbon.  It  is  nearly  insoluble  in 
water  (about  i  part  in  10,000)  and  dilute  alkaline  and  acid  liquids; 
sparingly  soluble  in  alcohol  (i  in  about  50),  but  more  readily  in 
absolute  alcohol  (i  in  25);  and  with  facility  in  ether,  chloroform,  and 
carbon  disulphide.  It  is  also  dissolved  by  many  essential  oils,  and 
sparingly  by  glycerol,  benzene,  and  petroleum  spirit. 

lodoform  is  employed  in  medicine  especially  as  an  antiseptic  dress- 
ing. Its  chemical  reactions  closely  resemble  those  of  chloroform.  Its 
microscopic  appearance  is  very  characteristic,  the  usual  forms  being 
hexagonal  plates,  stars,  and  rosettes. 

lodoform  may  be  extracted  from  urine  and  other  aqueous  liquids  by 
agitation  with  ether.  On  allowing  the  ethereal  layer  to  evaporate 
spontaneously,  the  iodoform  may  sometimes  be  recognised  by  ex- 
amining the  residue  under  the  miscroscpe.  If  no  distinct  forms  are 
observable,  the  residue  should  be  taken  up  with  a  little  absolute  alcohol, 
and  three  or  four  drops  of  the  clear  solution  added  to  a  minute  quantity 
of  a  solution  of  phenol  in  sodium  hydroxide.  The  mixture  is  cautiously 
heated,  when  a  red  deposit  will  be  formed  at  the  bottom  of  the  tube, 
soluble  in  dilute  alcohol  with  crimson  colour. 


IODOFORM.  283 

Commercial  lodoform. — On  agitation  with  water,  iodoform  should 
not  yield  a  liquid  precipitable,  after  nitration,  by  barium  chloride  or 
silver  nitrate.  It  should  leave  no  soluble  residue  on  ignition  in  the  air; 
and  should  be  wholly  soluble  in  boiling  alcohol,  but  insoluble  in  brine. 

Picric  acid  has  been  used  as  an  adulterant  of  iodoform  (Pharm. 
Jour.  [3],  1883,  14,  493).  It  may  be  detected  by  agitating  the 
sample  with  dilute  solution  of  sodium  carbonate,  carefully  neutralising 
the  nitrate  with  acetic  acid,  and  adding  potassium  nitrate,  when  a  yellow 
low  precipitate  of  the  sparingly  soluble  potassium  picrate  will  be  thrown 
down.  The  iodoform  may  also  be  separated  by  treating  the  sample 
with  sodium  hydroxide  solution  and  agitating  the  liquid  with  chloro- 
form, when  only  the  picric  acid  will  remain  in  the  aqueous  liquid. 
Picric  acid  may  also  be  detected  by  the  reddish-brown  colouration 
produced  on  heating  the  cold  aqueous  solution  of  the  sample  with 
potassium  cyanide. 


SUGARS. 


E.  FRANKLAND  ARMSTRONG,  D.  Sc.,  PH.  D.,  A.  C.  G.  I. 

Under  the  generic  name  of  sugars  is  included  a  large  number  of 
substances  occurring  naturally  in  the  animal  or  vegetable  kingdoms  or 
produced  from  the  so-called  glucosides  by  the  action  of  ferments  or 
dilute  acids. 

The  sugars  constitute  a  group  of  closely-allied  compounds,  in  many 
cases  distinguishable  from  each  other  only  with  considerable  difficulty, 
while  their  quantitative  separation  is  frequently  impossible  in  the 
present  condition  of  chemistry. 

As  a  class,  the  sugars  are  crystallisable,  readily  soluble  in  water, 
somewhat  less  soluble  or  wholly  insoluble  in  alcohol,  and  insoluble  in 
ether  and  other  solvents  immiscible  with  water. 

A  sweet  taste  is  possessed  by  nearly  all  sugars  to  a  greater  or  less 
extent.  Glycerol  and  glycol  have  a  sweet  taste,  and,  like  the  sugars, 
are  polyatomic  alcohols. 

In  many  cases  the  sugars  exert  a  powerful  rotatory  action  on  a  ray 
of  polarised  light,  the  direction  and  extent  of  the  rotation  being  pe- 
culiar to  each  sugar.  Hence  the  optical  activity  is  a  valuable  means 
of  estimating  and  differentiating  sugars. 

Constitution  and  Classification  of  Sugars.1 — The  sugars  proper 
are  aldehydes  or  ketones  of  hexatomic  alcohols  and  may  be  obtained 
from  these  by  limited  oxidation  or,  conversely,  converted  into  them  by 
reduction.  They  are  divided  into  three  great  groups,  viz.,  (i)  the  mono- 
saccharides  or  glucoses;  (2)  the  di-saccharides  or  saccharoses,  and  (3) 
the  poly-saccharides;  e.  g.,  starch,  cellulose,  etc.  They  mostly  contain 
6,  or  a  multiple  of  6,  atoms  of  carbon,  and  hydrogen  and  oxygen  in  the 
proportion  of  2:1. 

1  Nomenclature. — To  avoid  confusion  in  the  following  pages,  the  term  sucrose  has  been 
used  as  the  more  scientific  term  for  both  cane  and  beet  sugar,  whilst  the  term  cane  sugar 
describes  the  commercial  article  irrespective  of  origin.  The  word  glucose  is  restricted  to 
the  commercial  product  from  starch,  and  dextrose  is  used  for  the  pure  sugar  CeH^Oe. 
laevulose  for  the  corresponding  ketose  derived  from  cane  sugar.  The  disaccharide,  milk 
sugar  is  also  spoken  of  as  lactose.  Maltose  is  applied  to  the  disaccharide  derived  from  starch. 

The  abbreviation  A.  O.  A.  C.  indicates  the  official  and  provisional  methods  of  analysis 
adopted  by  the  Association  of  Official  Agricultural  Chemists  and  published  by  the  United 
States  Department  of  Agriculture,  Bureau  of  Chemistry  as  Bulletin  107,  September,  1907, 
superseding  Bulletins  46  and  65. 

28; 


286  SUGARS. 

The  Monosaccharides. — To  this  group  belong  the  naturally  oc- 
curring sugars  containing  5  and  6  carbon  atoms,  known  as  pentoses 
and  hexoses  and  also  the  closely  related  synthetical  sugars  with  3,  4, 
7,  8,  and  9  carbon  atoms.  They  are  characterised  by  the  following 
general  properties : 

1.  They  are  easily  oxidised  and  reduce  Fehling's  solution. 

2.  They  form  with  phenylhydrazine  and  acetic  acid  sparingly  solu- 
ble crystalline  osazones. 

3.  Those  hexoses  which  occur  naturally  undergo  alcoholic  fermen- 
tation with  yeast. 

4.  They  form  additive  compounds  with  hydrogen  cyanide. 

The  Disaccharides. — This  group  consists  of  sugars  of  the  formula 
C12H22On;  e.g.,  cane  sugar,  milk  sugar,  maltose,  melibiose  and  others 
formed  by  the  union  of  two  monosaccharide  residues  through  an 
oxygen  atom.  It  may  also  be  extended  to  include  sugars,  such  as 
ramnose,  formed  by  the  union  of  three  or  more  monosaccharide  resi- 
dues. The  general  properties  of  the  members  of  this  group  are : 

1.  They  are  converted  on  hydrolysis  by  mineral  acids  or  by  specific 
enzymes  into  monosaccharides. 

2.  They  are  not  directly  fermentable  unless  first  hydrolysed. 

The  Polysaccharides. — This  group  includes  substances  of  high 
molecular  weight,  of  the  general  formula  wC6H10O5  such  as  cellulose, 
starch,  glycogen  and  dextrin.  They  are  amorphous  substances  and 
yield  simpler  saccharides  or  ultimately  monosaccharides  on  hydrolysis. 

The  following  tables  show  the  origin  and  leading  characteristics  of 
the  more  important  mono-  and  disaccharides. 

Isolation  of  Sugars. — The  quantitative  analysis  of  complex  arti- 
ficial or  natural  carbohydrate  mixtures  is  one  of  the  most  difficult 
problems  in  organic  analytical  chemistry.  Indirect  methods  have 
almost  invariably  to  be  employed  and  errors  in  the  estimation  are  apt 
to  become  additive. 

The  general  methods  by  which  sugars  are  isolated  in  the  proximate 
analysis  of  animal  and  vegetable  substances  depend  much  on  the 
nature  of  the  associated  bodies.  Principles  of  separation  commonly 
utilised  are:  the  removal  of  proteins  bodies  by  heat  or  precipitation; 
the  precipitation  of  dextrin  and  other  gummy  matters  by  alcohol;  the 
removal  of  organic  acids  and  various  other  matters  by  lead  acetate; 
concentration  of  the  solution  with  a  view  to  promoting  crystallisation; 
and  the  detection  and  estimation  of  the  sugars  present  by  their  re- 


UONOSACCHARIDES. 


287 


oJ  6   «J  ^ 

<U  -o 

•    y 

i   _i. 

.1    bO 

C 

4?    O 

X    — 

o 

2  43  -5    >^ 

*"  "g 

eS  -^ 

«+«    c 

o  •£ 

"2 

^  -2; 

C    S 

c  -5  £  2 

C  ^ 

•fl 

'35  cx 

*£*•> 

u    _,    S  xV 

JH     O  ^    CO 

g| 

=31 

SB 

| 

l§ 

f| 

>§.2 

ll 

.a-S 

C 

l||| 

^-    ^J 

l| 

1  e 

^ 

Is 

22 

.2 

"S  c  """Eb 

>^   O    c3 

!i 

*°  § 

§ 

rt  g 

CO     3 

1 

l^  1^ 

fc 

§| 

I"*. 

2 

IT 

0^ 

c 

0 

23 

)-.    ^    O    ^ 

_«  15 

^  es 

OT      & 

•2 

^  M 

3 

B 

^    CJ  p^    ^ 

3.y 

oO     O 

S 

T3 

"u 

0 

o  'S      £ 

-2  I 

55  ^ 

S  -^ 

8 

a*  3 

n3 

X! 

S|j£ 

c/3    O 

•  —  —  — 

Is 

TJ 

11 

2 

.2^ 

S 

I 

CJ 

*G  ^J?  aj 

•sg 

u  ° 

jS 

1  § 

^ 

<u 
£ 

0 

slightly  sweet,  redv 
rbitol  on  reductioi 
urns  brown  with  a 
in  insoluble  osazor 
es. 

[extrose.  Forms  a 
.zone  as  dextrose, 
es. 

e.  Fermented  wi 
Icitol  on  reduction 

e  than  dextrose. 
Properties  similar 

t/5 
1 

CL>    ' 
1 

ij! 

-O  42  'u 

rabinose.  Forms 

la^ll 

s°l 

ill 

g    10  X! 

ess  solubl 
Yields  du 
acid. 

[ore  solubl 
mented. 
osazone. 

g 

«« 

§    C  ^ 

5-S-s 
5-81 

imilar  to  a 
reduction 

> 

09 

J 

3 

* 

* 

o> 

0 

0 

So 

0 

. 

o 

o 

0 

0 

III 

0) 

n 

10 

H 

H 

CO 

f 

f 

o 

H 

S 

*-$ 

•* 

S-i 

0) 

CO 

a 

*8 

•  S 

1 

1 

a 

<u 

^s 

li 

§ 

3 

1 

C 

O 

§ 

e-B 

^a 

^     CO 

c 

_C 

a 

CO 

11 

cu  rf  o 

'§  1 

c/T 

*5 
C 

1 

1 

•j 

[0*0  2^ 

c/5 

*0    ^ 

3 

o 

"o 

"o 

0 

111 

W 

C 

h 

|l 

| 

o>  S 

ft'C 

5 

1 

g 

5 

C? 

5 

O 

2 

• 

2 

§ 

§ 

U 

9 

a"jj 

| 

1 

ail 

jj 

§0 

5? 

1 

§ 

C 

1 

O 

TJ 

Ketohexos 
d-Lsevul< 

43 

T3 

1 

§ 

X* 

288 


SUGARS. 


C'd'S 

•g 

§^S 

5>  o 

§' 

-I 

-a  c" 

••S'5  c 

fl 

y    O  ,£ 

'S  o 

e 

"c  ~ 

«J  ro  o 

en   q   c3 

CJ 

u 

u 

(U    P 

T3    D    g 

6  73  'O 

J3  ~ 

J5 

OH 

s  a 

'M^ 

tf 

&  s  g 

O  bo 

M 

ri 

t/5 

1! 

O    ^ 

•  'S  S 

.2  'c 

C 

0 

'O  "^   ^ 

o' 

o  '^  [ii 

"S  rt 

03 

c 

o 

^  o 

'o  T3    P 

8 

•  rj   ^ 

^  oj 

<y 

£ 

rt  "£j 

(GLUCOSES)  .  —  CONTINUED. 

Other  characters 

Very  soluble  in  water.  Forms  oxalic  and  saccharic  a 
Chars  with  cone.  H2SO4.  Very  easily  hydrolyse 
and  by  invertase  to  a  mixture  of  dextrose  and  laevul 
only  after  inversion  by  yeast. 

Hydrolysed  by  treh'alase  to  two  molecules  of  dextr< 
exhibit  mutarotation  or  form  an  osazone. 

Less  soluble  than  dextrose.  Exhibits  mutarota 
osazone  soluble  in  hot  water.  Hydrolysed  by 
readily  by  maltase  to  two  molecules  of  dextrose, 
inversion  by  yeast  enzymes. 

Less  soluble  than  maltose  and  forms  mucic  acid  on  ox: 
very  similar.  Hydrolysed  by  lactase  to  dextros 
Not  fermented  by  ordinary  yeast. 

Mutarotates.  Hydrolysed  by  melibiase  to  dextroj 
Fermented  by  bottom  but  not  by  top  yeasts. 

Hydrolysed  by  acids  to  dextrose  and  fructose, 
osazone.  Not  hydrolysed  by  invertase. 

Does  not  form  a  hydrazone  or  osazone  nor  mutarol 
after  hydrolysis.  Converted  into  sucrose  and  gala 
and  into  lasvulose  and  melibiose  by  invertase. 

S 

o 

°XO 

o 

o 

OC 

o 

0 
1*5 

o 

00 

0^ 

Q 

*o  5  o 

"2 

o 

N 

H 

0 

vO 

M 

xn 

H 

M 

OH  JH   """^ 

1 

1 

I 

1 

i 

I 

w 

O! 

.^ 

.  w          . 

,(  ( 

*-M 

IM 

U 
U 

"5, 

c3 

».i 

c| 

0 

g 

0 

d 

? 

O 
O 

a 

£  " 

.2  ^ 

o  Q 

c/i 

"o  In 

1 

S 

11 

I 

g-a 

«j  ^ 

"c5 

4^    >% 

V 

£ 

-0  "S 

m 

C  a3 

"5"S 

g 

x£ 

£ 

^  r" 

oT 

^      Ert 

o 

cd 

X!   ~ 

^  o 

c 

S  <j 

£ 

t> 

jSj 

u 

cj     ^ 

rS 

"g 

0  »T 

2  c,; 

6 

SoS 

3  J 

11 

g 

tS'u 

•i'S 

§> 

3 

in 

H  " 

1 

S 

f2rt 

i 

3 
in 

0 

. 

§      ~0 

^  O 

nf 

q 

OJ 

U 

p| 

£  v 

S 

u 

2 

li 

. 

<<  ^   • 

rt 

s 

o 

O    • 

t/5 

t/3 

B   (xo  01 

^1 

'S   So 

15 

^  o 

So 

*(^ 

c 

8  S  § 

1   % 

1 

|| 

1 

2 

H 

|i| 

^^ 

06   W  »*< 

^ 

5 

H 

SACCHAROMETRY. 


289 


actions  as  reducing  agents,  and  their  relations  to  polarised  light.  A 
third  mode  of  determination  is  based  on  the  sp.  gr.  of  the  saccharine 
solution.  Other  useful  processes  for  estimation  or  differentiation  are 
based  on  the  behaviour  of  the  sugars  with  yeast,  and  on  treatment  with 
concentrated  and  dilute  acids. 

Phenylhydrazine  is  of  great  value  as  a  qualitative  reagent  and  the 
asymmetrically  disubstituted  hydrazines  may  in  some  cases  be  used 
with  advantage.  When  dealing  with  sugar  solutions  it  is  important 
to  avoid  carefully  the  presence  of  alkali.  The  general  methods  will 
be  described  in  the  following  sections,  before  dealing  with  the  special 
application  of  these  and  other  processes  to  the  examination  of  particu- 
lar sugars  or  saccharine  substances. 

Specific  Gravity  of  Saccharine  Solutions. — Solutions  of  equal 
strengths  containing  different  carbohydrates  have  approximately  the 
same,  though  not  strictly  identical,  sp.  gr.  In  other  words,  the  sp.  gr. 
of  the  solution  depends  chiefly  on  the  amount  of  solid  dissolved. 

The  following  table  shows  the  sp.  gr.  of  carbohydrate  solutions 
under  three  different  conditions.  The  figures  refer  in  all  cases  to 
15.5°  (60°  F.),  water  at  the  same  temperature  being  taken  as  1000. 


Substance  in 
solution 

Formula 

Specific  gravity  of  solutions 
containing 

Observer 

a 
4.2i%of 
carbo- 
hydrate. 

b 
10  grm. 
solid  per 
loogrm. 

c 

10  grm. 
solid  per 

100  C.C. 

Dextrose  

C6Hi2O6 

1042.1 
1042  .0 
1042.4 
1042  .  i 
1042.3 
1040.6 
1040.6 
1040.3 
1040.1 
1040.8 
1041.1 

1041.2 

1041  .2 
1039.0 
1039-2 

1039.  r 
1034.9 

1040.0 
1039.9 
1040.3 
1040.0 
1040.2 
1040.6 
1040.6 
1040.3 
1040.1 
1040.8 
1041  .  i 
1038.9 
1040.4 

1041  .1 
1041  .0 
1041.3 
1039.0 

1038.5 
1038.4 
1038.8 
1038.5 
1038.7 
1039.1 
1039.0 

1038.6 
1039.3 
1039.5 
1037.5 
1038.9 

1039.5 
1039.4 
1039.7 
1037.5 

F.  Salomon. 
A.  H.  Allen. 
G.  H.  and  R.i 
A.  H.  Allen. 
Chancel. 
O.  Hehner. 
G.  H.  and  R.* 
Brix;  Gerlach. 
Brown  and  Heron.1 
Brown  and  Heron.2 
O'Sullivan,  1879. 
Chas.  Graham. 
Muspratt. 
G.  H.  and  R.i 
G.  H.  and  R.i 
O'Sullivan,  1879. 
H.  T.  Brown,  1884. 
Brown  and  Heron.2 
G.  H.  and  R,1 

Starch  glucose.  . 

Invert  sugar  .            

2C6H12O6J 

Ci2H22Ou 
Ci2H22On  -j 

Ci2H22On  | 
j 

Milk  sugar  "  

Cane  sugar  
Maltose 

Malt  extract 

pale  
brown  

Dextrin 

I 

*Ci2H20Oio  { 

yCi2H2oOio 
C12Hi8O9(?) 

Starch  paste 

Caramel  

1.  Report  on  Original  Gravities,  1852  by  Graham,  Hofmann  and  Redwood. 

2.  Trans.  Chem.  Soc.,  1879,  35i  569. 

VOL.  I — 19 


SUGARS. 

In  practice  it  is  convenient  to  assume  the  solution  densities  of  the 
carbohydrates  to  be  uniformly  1.0386  for  a  concentration  of  10  grm. 
per  100  c.c.  whence  the  sp.  gr.  of  the  sugar  in  a  state  of  solution  is  1.628. 
It  follows  that  the  sum  of  the  carbohydrates  present  in  an  aqueous 
solution  may  be  found  approximately  by  allowing  an  increase  of  3.86 
in  density  for  each  i  grm.  of  carbohydrate  in  100  c.c.  of  the  liquid. 
This  figure  is  correct  for  very  dilute  solutions,  but  for  those  containing 
more  than  12  grms.  of  solids  the  divisor  3.85  gives  closer  results.1 

W  =  ~g°°°where  W  =  grm.  of  solids  in  100  c.c.  and  D  =  the  sp.  gr. 
of  the  solution  at  60°  F.  or  W  =  ^^  —  where  w  =  weight  of  solids 
in  100  parts  by  weight  of  the  liquid. 

The  foregoing  formula  is  applicable  for  carbohydrate  solutions  of 
moderate  strength;  in  case  the  sample  is  too  dense  to  determine  the 
density  directly  a  weighed  portion  of  it  must  first  be  diluted  with  a 
weighed  quantity  of  water,  or  a  weighed  portion  must  be  dissolved 
and  diluted  to  a  known  volume  of  water.  In  the  first  instance  : 

Percentage  of  solids  in  the  undiluted  material  =  —  -  where  S  = 
percentage  of  solids  in  the  diluted  material,  W  =  weight  of  the  diluted 
material,  w  =  weight  of  the  sample  taken  for  dilution. 

When  the  dilution  is  made  to  a  definite  volume: 

Percentage  of  solids  in  the  undiluted  material  =VDS/w,  where  V  = 
volume  of  the  diluted  solution,  D  =  sp.  gr.  of  the  diluted  solution,  S  = 
percentage  of  solids  in  the  diluted  solution,  w  =  weight  of  the  sample 
taken  for  dilution. 

In  breweries  it  is  often  convenient  to  ascertain  the  sp.  gr.  of  the  wort 
at  a  temperature  above  that  of  60°  F.  (=15.5°),  in  which  case  the 
sp.  gr.  as  observed  by  the  hydrometer  can  be  calculated  into  the  corre- 
sponding number  for  a  temperature  of  60°  F.  in  the  following  manner: 

To  unity  add  .004  for  every  degree  sp.  gr.  above  1000  (g)  shown 
by  the  hot  wort,  and  .01  for  each  Fahrenheit  degree  of  temperature 
(/)  above  60°  F.  Multiply  the  sum  of  these  by  i/io  of  the  number  of 
Fahrenheit  degrees  above  60°  F.,  when  the  product,  added  to  the  sp. 
gr.  of  the  hot  wort,  will  be  a  number  representing  the  sp.  gr.  of  the 
liquid  at  60°  F.  The  rule  is  expressed  by  the  following  formula: 


G  =t  +         _  _  + 

\  IOOO  IOO      /         IO 

1  Brown  and  Heron  (Trans.  Chem.  Soc.,  1879,  35,  644)  have  laid  down  a  curve  by  which 
the  strength  of  cane-sugar  solutions  can  be  readily  ascertained  in  all  cases  of  less  density 
than  1  1  so. 


SACCHAROMETERS.  29  1 

Thus,  if  the  wort  be  found  to  have  a  sp.  gr.  of  1052.0  at  a  temperature 
of  110°  F.,  then  by  the  formula: 

(1052  —  1000)4         no  —  6o\  no  —  60 

1000  100      /        10 

G  =  (i  +  .208  +  .5)5  +  1052  =  1060.54 

Saccharometers.  —  Various  modifications  of  the  hydrometer  have 
been  devised  and  used  for  ascertaining  the  sp.  gr.  of  saccharine 
solutions. 

Bates'  brewers'  saccharometer  is  much  used  for  testing  the  strength 
of  beer-  worts,  and  hence  it  is  described  under  "Malt." 

On  the  Continent,  Balling's  saccharometer  is  much  used.  If 
B=degrees  of  Balling  and  b  those  of  Bates,  the  indications  of  one  in- 
strument may  be  calculated  to  those  of  the  other  by  the  following 
formulae  : 

2606 
B  =  -        —  -  ;  and  b 


360  +  b  260  —  B 

The  saccharometer  of  Brix  is  practically  the  same  as  that  of  Balling. 
In  each,  the  number  of  degrees  is  identical  with  the  percentage  by 
weight  of  cane  sugar  in  the  solution. 

The  Brix  spindle  should  be  graduated  to  tenths.  It  is  therefore 
desirable,  for  accuracy,  that  the  range  of  degrees  recorded  by  each 
individual  spindle  be  as  limited  as  possible,  this  end  being  best  secured 
by  the  employment  of  sets  consisting  of  not  less  than  three  spindles. 
The  solutions  should  be  as  nearly  as  possible  of  the  same  temperature 
as  the  air  at  the  time  of  reading,  and  if  the  variation  from  the  tempera- 
tures of  the  graduation  of  the  spindle  amount  to  more  than  i°,  com- 
pensation must  be  made  by  reference  to  the  table  of  corrections  for 
temperature,  page  293.  This  temperature  should  be  17.5°  C.  Before 
taking  the  sp.gr.  of  a  juice,  it  should  be  allowed  to  stand  in  the  cylinder 
until  all  air  bubbles  have  escaped. 


2Q2 


SUGARS. 


A  TABLE  FOR   THE   COMPARISON    OF   SPECIFIC    GRAVITIES, 
DEGREES  BRIX  AND  DEGREES  BAUME. 


Degree 

Degree 

Degree 

Brix     or 

Brix  or 

Brix  or 

per  cent, 
by 

Specific 
gravity 

Degree 
Baume' 

percent, 
by 

Specific 
gravity 

Degree 
Baume 

percent, 
by 

Specific 
gravity 

Degree 
Baume" 

weight 

weight 

weight 

of  su- 

of su- 

of su- 

crose 

crose 

crose 

I     0 

.00388 

0.6 

33-0 

. 
.14423 

18.5 

6,0 

.31989 

35-6 

2     0 

.00779 

i  .1 

34-0 

.14915 

19.05 

66  .0 

.32601 

36.1 

3   o 

.01173 

1.7 

35-0 

.15411 

19.6 

67  .0 

•33217 

36.6 

4  o 

.01570 

2.3 

36.0 

.15911 

20.  i 

68.0 

.33836 

37-1 

5   o 

.01970 

2.8 

37-0 

•16413 

20.7 

69.0 

.34460 

37.6 

6  o 

.02373 

3-4 

38.0 

.16920 

21.2 

70.0 

.35088 

38.1 

7   o 

.02779 

4.0 

39.0 

•17430 

21.8 

71.0 

•35720 

38.6 

8  o 

.03187 

4-5 

40.0 

•17943 

22.3 

72  .0 

•36355 

39-1 

9   o 

•03599 

S-i 

41.0 

.18460 

22.9 

73-o 

•36995 

39-6 

10  o 

.04014 

5-7 

42.0 

.18981 

23.4 

74-0 

•37639 

40.1 

II     0 

.04431 

6.2 

43-0 

•1950S 

23.95 

75-0 

•    .38287 

40.6 

12     0 

.04852 

6.8 

44-0 

.20033 

24-5 

76.0 

•38939 

41.  i 

13   o 

.05276 

7-4 

45-0 

.20565 

25.0 

77.o 

•39595 

41.6 

14  o 

•05703 

7-9 

46.0 

.21100 

25-6 

78.0 

.40254 

42.1 

15     0 

.06133 

8.5 

47-0 

.21639 

26.1 

79-0 

.40918 

42.6 

16  o 

.06566 

9.0 

48.0 

.22182 

26.6 

80.0 

.41586 

43-1 

17  o 

.07002 

9.6 

49-0 

.22728 

27.2 

81.0 

.42258 

43-6 

18  o 

.07441 

10.  I 

50.0 

.23278 

27-7 

82.0 

.42934 

44.1 

19  o 

.07884 

10.7 

Si.o 

.23832 

28.2 

83-0 

•43614 

44.6 

20  o 

.08329 

II  -3 

52.0 

.24390 

28.8 

84.0 

.44298 

45-1 

21     0 

.08778 

II  .8 

53-0 

.24951 

29-3 

85.0 

.44986 

45-5 

22     0 

.09231 

12.4 

54.0 

.25517 

29.8 

86.0 

.45678 

46.0 

23   o 

.09686 

13-0 

55-0 

.26086 

3'0.4 

87.0 

•46374 

46.5 

24  o 

.10145 

13-5 

56  .0 

.26658 

30.9 

88.0 

•47074 

47-0 

25   o 

.  10607 

I4-I 

57-0 

.27235 

31-4 

89.0 

•47778 

47-45 

26  o 

.11072 

14.6 

58.0 

.278l6 

31  -9 

90.0 

.48486 

47-9 

27   o 

.11541 

15-2 

59-0 

.28400 

32.5 

91  .0 

.49199 

48.5 

28  o 

.12013 

15-7 

60.0 

.28989 

33-0 

92  .0 

.49915 

48.9 

29  o 

.12488 

16.3 

61  .0 

.29581 

33-5 

93-0 

•50635 

49-4 

30  o 

.12967 

16.8 

62  .0 

.30177 

34-0 

94-0 

.51359 

49.8 

31  o 

.13449 

17.4 

63  .0 

•30777 

34-5 

95-0 

.52087 

50.3 

32   o 

•13934 

17-95 

64.0 

.31381 

35-1 

The  degrees  of  this  table  are  apparently  those  of  the  Gerlach  scale: 
SP-  gr-=^ 


If  the  determination  be  made  at  any  other  temperature  than  17.5, 
the  result  should  be  corrected  by  the  use  of  the  following  table: 


SACCHAROMETERS. 


293 


TABLE    FOR    CORRECTION    OF    THE    READINGS    OF    THE    BRIX 
SPINDLE  WHEN   THE   READING   IS   MADE   AT   OTHER 

THAN  THE  STANDARD  TEMPERATURE,  17.5°. 
(For  temperatures  below  17.5°  the  correction  is  to  be  subtracted.) 


Tempera- 
ture 

Degree  Brix  of  the  Solution 

o 

5           10 

15 

20 

25 

30 

35          40 

50 

60     j     70 

i 

75   ' 

0 

0.17 

0.30 

0.41 

o.5  = 

o.63 

0.72 

0.82 

0.92 

0.98 

i  .11 

I  .22 

1.25 

1.29 

5 

0.23    0.30 

0-37 

0.44 

0.52 

0.59 

0.65 

0.72 

o.75 

0.80 

0.88 

0.91 

0.94 

10 

0.20      0.26       0.29 

0-33 

0.36 

0.39 

0.42     0.45  !  0.48  1  0.50 

0.54 

0.58 

0.61 

ii 

12 

0.18     0.23     0.26 

O.l6  !   O.20       0.22 

0.28 
0.24 

0.3I 
0.26 

o.34 
0.29 

0.36    0.39 

0.31    0.33 

0.41 
0-34 

0.43 
0.36 

0.47 
0.40 

0.5O 
0.42 

0.53 
0.46 

13 

0.14  I  o  .  18 

o  .  19 

0.21 

0.22 

0.24 

0.26 

0.27 

0.28     0.29 

0.33 

0.35 

0.39 

14 

0.12       O.I5 

0.16 

0.17 

0.18 

0.19 

0.21 

O.22   I   O.22 

0.23 

o  .  26 

0.28 

0.32 

15 

0.09     o.i  i 

O.I2 

o  .  14 

0.14 

0.15 

0.16 

0.17     0.16     0.17 

0.19 

O.2I 

0.25 

16 

0.06       0.07 

0.08 

0.09 

0.  10 

O.IO 

0.  II 

0.12       0.12       O.I2 

0.14 

0.16 

0.18 

17 

0.02       0.02 

0.03 

0.03 

0.03 

o  .04 

0.04     0.04 

0.04     0.04 

0.05 

0.05 

0.06 

18 

0.02       0.03 

0.03 

0.03 

0.03 

0.03 

0.03    0.03 

0.03 

0.03 

0.03 

0.03 

O.02 

19 

0.06     .0.08 

0.08 

0.09 

0.09 

O.IO 

O.IO  I   O.IO 

O.IO 

0.  10 

O.IO 

0.08 

o  .06 

20 

0.  II       0.14 

0.15 

0.17 

0.17 

0.18 

0.18     0.18 

0.19    0.19 

0.18 

0.15 

O.II 

21 

0.16 

0.20 

0.22 

0.24 

0.24 

0.25 

0.25    0.25 

0.26 

0.26 

0.25 

O  .  22 

0.18 

22 

0.21 

0.26 

0.29 

0.31 

0.31 

0.32 

0.32     0.32 

0.33 

0.34 

0.32 

O.29 

0.25 

23 

0.27 

0.32 

0-35 

0.37 

0.38 

o.39 

0.39    0.39 

0.40 

0.42 

0.39 

0.36 

0.33 

24 

O.32       0.38 

0.41 

0.43 

0.44 

0.46 

0.46 

0.47 

0.47 

0.50 

0.46 

0.43 

0.40 

25 

0.37 

0.44    0.47 

0.49 

0.51 

0.53 

0.54    0.55 

0.55 

0.58 

0.54 

0.51 

0.48 

26 

0.43     0.50     0.54 

0.56 

0.58 

0.60 

o  .61     0.62 

0.52 

o  .66 

0.62 

0.58 

0.55 

27 

0.49     0.57  i  0.61 

0,63 

0.65 

0.68 

0.68 

o  .69 

0.70 

o.74 

0.70 

o  .65 

0.62 

28 

0.56     0.64  |  0.68 

0.70 

0.72 

0.76 

0.76 

0.78 

0.78 

0.82 

0.78 

0.72 

0.70 

29 

0.63     0.71     0.75 

0.78 

0.79 

0.84 

0.84 

0.86 

0.86 

0.90 

0.86 

0.80 

0.78 

30 

o  .  70 

0.78 

0.82 

0.87 

0.87 

0.92 

0.92     0.94 

0.94 

0.98 

o.94 

0.88 

0.86 

35 

I  .10 

1  .17 

I  .22 

1.24 

1-30 

1.32 

1-33  i  i-35 

1.36 

1.39 

1-34 

i  .27 

1.25 

40 

1.50 

1.61 

1.67 

I.7I 

i  .73 

i  .79 

i  .79  ,  i  .80 

1.82 

1.83 

1.78 

i  .69 

1.65 

50 

2.65 

2.71 

2.74 

2.78 

2.80 

2.80  i  2  .80 

2.80 

2.79 

3-70 

2.56 

2.51 

60 

.... 

3.87 

3.88 

3-83 

3-88 

3-88 

3-88     3-88 

3-90 

3-82 

2.70 

3-43 

3-41 

70 
80 



5-17 

5.i8 
6  .62 

5-20 
6  .  5Q 

5-14 

6    c/i 

5-13 
6.46 

5  .10     5  .08 
6.38     *    *« 

5  .06 
6  .26 

4-90 
6.06 

4.72 
5  .82 

4-47 

e     CQ 

4-35 
S  •  33 

90 

8.26 

8.16 

8!o6 

7  -97 

7  •  83 

7.71 

7-58 

7  .30 

6.96 

6J8 

6.37 

100 

IO.OI 

9.87 

9.72 

9.56 

9-39 

9.21 

9.03 

8.64 

\J  .  y  \J 

8.22 

£. 
7.76 

7.42 

Example. — A  sugar  solution  shows  a  reading  of  30.2°  Brix  at  30°. 
To  find  the  necessary  correction  for  the  conversion  of  this  reading  to 
the  reading  which  would  have  been  obtained  if  the  observation  had 
been  made  at  17.5°.,  find  the  vertical  column  in  the  table  headed 
30°  Brix,  which  is  the  nearest  to  the  observed  reading.  Follow  down 
this  column  until  the  number  is  reached  which  is  opposite  to  the  tem- 
perature of  observation — in  this  case  30°.  The  number  found,  0.92, 
is  to  be  added  to  the  observed  reading. 

Mohr  (Zeit.  Spiritusind,  1906,  29,  25)  has  recalculated  and  co- 
ordinated the  existing  data  relating  to  the  sp.  gr.  of  solutions  of  the 
different  sugars.  He  shows  the  percentage  by  weight  and  the  con- 
centration in  grm.  per  100  c.c.  for  each  of  the  sugars  with  the  cor- 
responding sp.  grs.  of  sucrose  solutions  of  the  same  concentration  at 
the  same  temperature  and  the  percentage  by  weight  of  cane  sugar  in 
solutions  of  the  same  sp.  grs. 


294 


SUGARS. 


ANHYDROUS  DEXTROSE  (Salomon,  Ber.,  1881,  14,  2711). 


Contents  of 
solution. 
Grm.  per  100 
c.c. 

Contents   of   solu-  «         .     .   .           «.JSp.     gr.    of    cane- 
tion.     %   by        bP-fIiu°tfiodneXattrOSe!  sugar  solution  of 

weight                   !?5*S?*+        same   concentra' 
I7.S/I7.S          !tionat£7.5°/i7.5° 

Contents  of  cane- 
sugar    solution    of 
same  sp.  gr.  as  dex- 
trose.   %  by 
weight. 

I  .00 

0.998                            .00375                          .00387 

0.967 

2  .00 

1.988 

.0075 

.00774 

i  .926 

3.00 

2.970 

.0115 

.01160 

2  .944 

4  .00 

3-945 

•0153 

•01547 

3-903 

S  .00 

4.912 

.0192 

.01933 

4.880 

6.00 

5.873 

.0230 

.02319 

5.825 

7  .00 

6.827 

.0267 

.02705 

6.740 

8.00 

7-773 

•0305 

.03089 

7.677 

9  .00 

8.714 

.0342 

•03475 

8.581 

10.00 

9.645 

.0381 

.03858 

9.527 

II  .00 

10.570 

.O42O 

.04243 

10.467 

12  .OO 

ii  .490 

•0457 

.04628 

II  -352 

13  .00 

12  .402 

.0495 

.05011 

12.257 

14.00 

13.309 

•  0533 

.05396 

I3-I55 

15  .00 

14.209 

.0571 

.05780 

14.047 

1  6  .00 

15  .IOO 

.0610 

.06161 

14.958 

1  7  .00 

15.984 

.0649 

.06542 

15.863 

18.00 

16.864 

.0687 

.06924 

16.740 

L^EVULOSE  (Ost.,  Lippman's  "Chem.  der  Zuckerarten,"  3d  Edition,  I,  819). 


Contents  of 
solution. 
Grm.  per  100 
c.c. 

Contents   of   solu- 
tion.    %  by 
weight. 

^^fea£? 

tionat20°/4° 

Contents  of  cane- 
sugar    solution    of 
same    sp.    gr.     as 
laevulose.    %  by 
weight. 

i  .01 

i  .0100 

.0021 

.OO2l6 

•  995 

1.03 

i  .0324 

.0022 

.00224 

.002 

2  .OI 

1.9949 

.0062 

.00600 

.047 

2.04 

2  .0263 

.0063 

.00612 

•  073 

5-03 

4-9395 

•0177 

.OI76l 

.961 

5.04 

4-9575 

.0178 

.01768 

.986 

5.06 

4.9710 

.0178 

•01773 

.986 

8.04 

7.8051 

•0295 

.02915 

7-891 

9.28 

8.9724 

.0341 

•03392 

9.018 

10.19 

9.8195 

.0379 

•03740 

9.941 

10.95 

10.5199 

.0405 

.04029 

10.570 

19.90 

18.5161 

.0748 

.07441 

18.605 

21.93 

20.2638 

.O82I 

.08213 

20.257 

33.56 

29-7995 

.  1263 

.12603 

29.857 

33.97 

30.1157                           -1279 

•12754 

30.193 

SACCHAROMETRY.  295 

INVERT  SUGAR  (Herzfeld,  Z.  Ver.  deut.  Zuckerind,  37,  912). 


Contents    of    pn_t»nt<.  Of 
solution.        Contents* 


Grm.  per 


bvht 
by  \veignt 


Sp.  gr.  of  invert  sugar  solution.  Contents    of 

Sp.  gr.  of  cane-  cane-sugar 
sugar  solution  of  solution  of 
same  concentra-  same  sp.  gr. 
tion  at  as  invert 


Ati7.5°/40   At  I7.5°/I7.5°   I7.5°/I7.S° 

sugar.  % 
by  weight. 

10.39 

10.0         .03901         .04034 

.04005 

10.07 

10.93 

10.5 

.04109 

•04243 

.04214 

10.57 

II  .47 

II  .0 

.04316 

.04450 

.04422 

ii  .07 

12  .02 

ii  -5 

.04527 

.04661 

.04632 

n-57 

12.57 

12  .0 

.04737 

.04871 

.04841 

12  .O? 

13-12 

12.5 

.04949 

.05083 

•05053 

12.57 

I3.67 

13.0 

.05160 

•05295 

.05264 

13  -07 

I4./8 

14.0 

-05588 

•05723 

.05690 

14.08 

15.90  > 

15.0 

.06018 

.06154 

.06118 

15.08 

I"  -03 

16  .0 

.06453 

.06590 

.06549 

1  6  .09 

I8.I7 

17.0 

.06889 

.07026 

.06983 

17  .10 

19.32 

18.0 

•07330 

.07468 

.07421 

i8.ii 

20.48 

19  .0 

.07772 

.07912 

.07862 

19.11 

2  I  .64 

20.0 

.08218 

•08357 

.08306 

20  .  1  1 

22.82 

21  .0 

.08665 

.08804 

.08753 

21  .11 

24  .  oo 

22  .0 

.09114 

.09254 

.09203 

2?  .11 

.   25.20 

23.0 

.09566 

.09707 

•09658 

23-11 

26.40 

24.O 

.10019 

.  10160 

.10115 

24  .10 

27  .62 

25  -o 

.10474 

.10616 

•10575 

25  -09 

28.84 

26.0 

.10930 

.11072 

•11039 

26  .07 

30.09 

27  .0 

•II433 

•II576 

.11506 

27-15 

ANHYDROUS  MALTOSE  (Salomon.  J.  prakt,  Chem.,  [2],  28,  82). 


Contents  of 
solution. 

Sn      or     of     cane    Contents  of   cane- 
Contents   of   solu-  Sp.  gr.  of  maltose     P-    8      j   .  •           r  sugar   solution    of 

Grm.  per  100 

tl0weig?t.by           JrlsV??.**        same  .concentra- 

same    sp.     gr.     as 
maltose.     %  by 

c.c. 

I7.5°/I7.5° 

weight. 

I  .0 

0.997 

.00393 

•00387 

i  .013 

2  .0 

1.987 

.00785 

.00774 

2  .015 

3-0 

2.969 

.01177 

.01160 

3-013 

4.0 

3-943 

.01568 

.01546 

3-998 

5-0 
6.0 

4.9H 
5.870 

•01953 
.02340 

.01932 
.02318 

4-963 
5-925 

7.0 

6.823 

.02733 

.02703 

6.895 

8.0 

7.768 

.03122 

.03087 

7-855 

9.0 

8.706 

•03515           I 

.03471 

8.812 

10.  0 

9.637 

.03900 

•03855 

9.746 

15.0 

14.192 

.05827 

•05773 

14.321 

20.  o 

18.587 

.07740 

.07680 

18.723 

25.0 

22.829 

.09650 

.09580 

22.982 

30.0 

26.928 

•II550 

.11472                        27.096 

Laevulose,  invert  sugar,  and  maltose  solutions  have  higher  sp.  gr. 
than  the  corresponding  solutions  of  cane  sugar,  whilst  those  of  dextrose 
have  lower  sp.  gr.  It  will  be  seen  that  the  use  of  the  cane-sugar 
tables  for  the  determination  of  other  sugars  involves  an  error  of  only 

o.i  %. 


296  SUGARS. 

Action  of  Strong  Acids  on  Sugars. — Organic  acids  act  on  sugars 
to  form  oxygen  esters.  In  presence  of  suitable  dehydrating  agents 
acetic  acid  or  acetic  anhydride  gives  rise  to  fully  acetylated  compounds, 
viz.,  the  pentacetate  in  the  case  of  the  glucoses  or  the  octacetate  of 
sucrose,  maltose,  or  lactose.  Dextrose  pentabenzoate  may  be  used  for 
the  detection  and  isolation  of  dextrose,  particularly  in  physiological 
fluids.  The  so'ution  is  shaken  for  an  hour  with  six  parts  of  benzoyl 
chloride  and  48  parts  of  18  to  20%  sodium  hydroxide  for  every 
part  of  dextrose  and  cooled  with  ice.  After  24  hours  the  pentaben- 
zoate may  be  recrystallised  from  alcohol.  It  forms  colourless  needles ; 
m.  p.,  179°. 

Nitric  acid  when  used  in  cold  concentrated  solution  gives  rise  to  nitric 
esters.  When  heated  with  dilute  or  moderately  concentrated  acid  the 
sugars  yield  oxidation  products,  of  which  mucic,  saccharic,  tartaric  and 
racemic  acids  are  the  most  constant  and  characteristic.  The  forma- 
tion of  mucic  acid  is  characteristic  of  galactose  and  also  of  di-  or  poly- 
saccharides  which  contain  galactose,  e.  g.,  milk  sugar  or  gums.  For  the 
estimation  of  galactose  as  mucic  acid,  see  under  Galactose,  p.  376. 

Sulphuric  Acid. — Dextrose  dissolves  in  cold  concentrated  sulphuric 
acid  without  any  colouration,  forming  dextrosesulphonic  acid.  This 
behaviour  distinguishes  dextrose  from  cane  sugar,  which  is  carbonised 
by  concentrated  sulphuric  acid  with  great  facility.  A  strong  syrup  of 
cane  sugar  mixed  with  concentrated  sulphuric  acid  is  immediately 
decomposed  with  evolution  of  sulphur  dioxide  and  other  volatile  prod- 
ucts, and  formation  of  a  bulky,  black,  carbonaceous  mass. 

Action  of  Dilute  Acids  on  Sugars.  Hydrolysis  or  Inversion.— 
When  an  aqueous  solution  of  cane  sugar  is  heated  with  dilute  sulphuric 
or  hydrochloric  acid,  the  solution  increases  in  sp.  gr.,  and  the  sugar 
loses  its  power  of  crystallising  readily.  This  change  in  properties  is 
attended  by  the  assimilation  of  the  elements  of  water,  with  formation 
of  the  mixture  of  dextrose  and  laevulose  known  as  inverted  or  invert 
sugar :  C12H22On  +  H2O  =  2C6H12O6.  The  rate  of  hydrolysis  depends 
mainly  on  the  proportion  of  acid  used,  its  chemical  activity,  and  the 
temperature  employed  in  the  operation.  When  cane  sugar  is  hydro- 
lysed  the  optical  activity  is  changed  from  right-  to  left-handed  or  is 
"inverted."  The  term  inversion  is  often  applied  generally  to  the 
process  of  hydrolysis  of  the  di-saccharides  whether  or  not  the  same 
optical  change  be  produced. 

The  property  of  undergoing  hydrolysis  when  heated  with  dilute 


HYDROLYSIS    OF    SUGARS.  297 

acids  is  common  to  all  the  di-  and  poly-saccharides.  The  follow- 
ing table  shows  the  products  of  hydrolysis  of  the  principal  di-  and  tri- 
saccharides : 

Di-saccharide.      =     Mono-saccharides. . 

Cane  sugar         =     dextrose  and  laevulose. 

Milk  sugar          =     dextrose  and  galactose. 

Maltose  =     dextrose. 

Melibiose  =     dextrose  and  galactose. 

Raffinose  =     laevulose,  dextrose  and  galactose. 

Sucrose  is  most  readily  and  certainly  inverted  by  adding  to  a  solu- 
tion containing  not  more  than  25  grm.  of  the  solid  per  100  c.c.  one- 
tenth  of  its  bulk  of  fuming  hydrochloric  acid,  and  then  heating  the 
liquid  to  70°  for  10  or  15  minutes.  Some  operators  prefer  dilute 
sulphuric  to  hydrochloric  acid,  and  heat  the  liquid  to  boiling  for  5  or 
10  minutes. 

Lactose  .is  less  readily  hydrolysed  than  sucrose,  being  unaffected 
by  boiling  for  ten  minutes  with  2  grm.  of  citric  acid  per  100  c.c.  of  the 
solution. 

The  differences  in  the  readiness  with  which  different  sugars  are 
hydrolysed  is  shown  in  the  following  table1  in  which  the  rate  of 
hydrolysis  by  hydrochloric  acid  at  about  70°  of  a  number  of  substances 
under  identical  conditions  is  recorded  relatively  to  the  most  stable 
compound  which  is  expressed  as  100. 

aMethyl-glucoside,  100 

/?Methyl-glucoside,  180 

aMethyl-galactoside,  540 

/SMethyl-galactoside,  880 

Salicin,  600 

Lactose,  720 

Maltose,  740 
Cane  sugar,                            about  900,000 

To  insure  complete  hydrolysis  of  carbohydrates  other  than  cane 
sugar,  dilute  solutions^— preferably  not  above  5  % — should  be  em- 
ployed and  the  heating  prolonged.  Meissel  (Z.  anal,  chem.,  22,  115) 
uses  3  %  sulphuric  acid  or  5  %  fuming  hydrochloric  acid,  obtaining  in 
the  former  case  a  conversion  of  98.5  %.  The  liquid  is  heated  in  a  water- 
bath  for  3  or  4  hours.  O'Sullivan  states  that  the  purest  yield  of  dex 

1E.  F.  Armstrong  Proc.  Roy.  Soc.  1904,  74,  188—194. 


298  SUGARS. 

trose  is  obtained  by  heating  30  grm.  of  the  saccharine  matter  in  100 
c.c.  of  i  %  sulphuric  acid  at  a  pressure  of  one  additional  atmosphere; 
pure  dextrose  results  after  20  minutes'  treatment.  When  the  inverted 
solution  of  a  sugar  is  to  be  decolourised  by  basic  lead  acetate  or  treated 
by  Fehling's  solution,  the  free  acid  contained  in  it  should  first  be  nearly 
neutralised  by  the  addition  of  sodium  carbonate. 

Action  of  Alkalies  on  Sugars. — Cane  sugar  is  not  attacked  by 
dilute  caustic  alkalies  or  alkaline  carbonates  in  the  cold,  and  only  very 
slowly,  if  at  all,  on  heating.  It  is  decomposed  by  boiling  with  concen- 
trated alkaline  solutions,  and  when  fused  with  potassium  hydroxide 
yields  potassium  oxalate  and  acetate  and  other  products.  Cane 
sugar  forms  a  few  well-established  compounds  with  bases  and  many 
with  salts. 

Dextrose  and  other  mono-saccharides  are  readily  decomposed  by 
alkalies.  When  heated  with  sodium  or  potassium  hydroxide,  dex- 
trose becomes  brown  at  60-70°,  and  decomposes  entirely  on  prolonged 
boiling. 

Fermentation  of  Sugars. — Dextrose,  fructose,  mannose,  and 
invert  sugar  are  fermentable  by  all  yeasts.1  Cane  sugar,  maltose,  lac- 
tose, melibiose  and  ramnose  are  fermentable  only  after  inversion  by 
dilute  acids  or  by  an  appropriate  enzyme.  Ordinary  yeast,  Saccharo- 
myces  cerevisia,  contains  the  enzymes  which  hydrolyse  cane  sugar  and 
maltose  and  can  ferment  both  these  sugars.  Fermentation  is  pre- 
ceded by  inversion  and,  indeed,  if  the  proportion  of  yeast  is  very  small, 
the  change  of  sucrose  does  not  go  beyond  the  formation  of  invert  sugar. 

To  recognise  the  presence  of  a  fermentable  sugar  by  means  of  yeast, 
care  must  be  taken  (i)  that  the  aqueous  solution  is  not  too  con- 
centrated (from  5  to  10  %  is  the  most  suitable  concentration) ;  (2)  that 
the  liquid  is  neutral  or  faintly  acid,  alkalinity  being  carefully  neutralised; 
(3)  that  the  liquid  is  wholly  free  from  antiseptics  of  any  kind  which 
would  prevent  the  alcoholic  fermentation. 

The  yeast  should  be  fresh,  free  from  starch  and  carefully  washed 
with  a  little  cold  distilled  water  before  use. 

5  to  10  c.c.  of  the  liquid  are  mixed  with  a  little  yeast,  placed  in  a 
test-tube  closed  with  a  plug  of  sterilised  cotton  wool,  and  incubated  at 
20-30°  for  a  few  hours.  In  a  positive  experiment  the  signs  of  fer- 
mentation are  unmistakable,  and  gentle  shaking  will  cause  the  bubbles 
of  gas  to  rise  to  the  surface.  It  is  always  desirable  to  make  a  blank 

^ee  E.  F.  Armstrong,  Proc.  Roy.  Soc.,  1905,  768,  600. 


FERMENTATION    OF    SUGARS.  299 

experiment  so  as  to  ascertain  positively  that  the  yeast  does  not  itself 
yield  any  notable  quantity  of  carbon  dioxide  under  the  conditions  of  the 
experiment. 

The  foregoing  process  may  readily  be  made  roughly  quantitative 
by  attaching  a  delivery  tube  and  collecting  the  gas  formed  over  mer- 
cury. More  accurate  results  are  obtained  by  using  an  apparatus  such 
as  is  employed  for  the  analysis  of  carbonates  and  determining  the  loss 
of  weight  during  fermentation.  The  dissolved  carbon  dioxide  may 
be  swept  out  by  a  current  of  air  before  the  final  weighing.  The  fer- 
mentation should  be  continued  as  long  as  any  notable  quantity  of  gas 
continues  to  be  evolved.  The  weight  of  carbon  dioxide  multiplied  by 
2.0454  gives  that  of  the  dextrose  fermented,  which  figure  multiplied  by 
0.95  gives  the  corresponding  weight  of  sucrose  or  maltose. 

Instead  of  measuring  or  weighing  the  carbon  dioxide  produced  it  is 
in  some  respects  preferable  to  estimate  the  alcohol  formed.  The 
process  is  conducted  as  already  described,  but  it  is  not  desirable  to  em- 
ploy less  than  50  or  100  c.c.  of  the  solution,  which  should  by  preference 
have  a  concentration  of  12  to  16  per  cent.;  0.5  grm.  of  pressed  fresh 
yeast  is  sufficient  in  most  cases,  especially  if  a  little  yeast-ash  be  added, 
but  it  is  desirable  to  add  a  little  more  yeast  at  the  end  of  the  action 
to  insure  that  no  further  fermentation  can  be  induced.  The  liquid 
should  be  kept  at  a  temperature  of  20°  to  25°  for  2  or  3  days,  after  which 
the  liquid  is  distilled  to  about  1/3,  the  distillate  weighed,  and  the  alco- 
hol contained  in  it  ascertained  from  the  sp.  gr.  The  weight  of  alcohol 
thus  found  when  multiplied  by  2.02  gives  the  dextrose  or  by  1.96 
the  sucrose  from  which  it  was  derived. 

Some  operators  prefer  to  employ  a  large  quantity  of  yeast,  such  as 
10  or  even  20  grm.  In  such  cases  it  is  very  desirable  to  conduct  a 
blank  experiment  with  the  same  quantity  of  yeast,  and  water,  side  by 
side  with  the  test  of  the  saccharine  liquid,  and  to  deduct  the  alcohol 
found  in  the  former  case  from  that  obtained  in  the  latter  before  calculat- 
ing to  the  equivalent  of  sugar.  A  still  better  plan,  perhaps,  is  to  fer- 
ment a  solution  of  sucrose  or  invert  sugar,  of  known  strength,  side  by 
side  with  the  samples,  when  the  amounts  of  sugar  in  the  two  liquids  will 
bear  to  each  other  the  same  proportion  as  the  amounts  of  alcohol  pro- 
duced by  their  distillation. 

Another  method  which  has  been  suggested  for  estimating  sugar 
from  the  results  of  its  fermentation  by  yeast  consists  in  noting  the 
"gravity  lost"  in  the  process;  that  is,  the  sp.  gr.  of  the  original  saccha- 


300  SUGARS. 

rine  solution  is  observed  and  compared  with  that  of  the  fermented  liq- 
uid, after  filtering,  washing  the  residue,  boiling  off  the  alcohol,  and  mak- 
ing up  the  solution  to  its  original  volume.  The  difference  is  the  "grav- 
ity lost"  by  the  fermentation.  The  "spirit  indication"  corresponding 
to  the  value  thus  found  is  ascertained  by  reference  to  the  table  on 
page  153,  and  this  figure  subtracted  from  1000  gives  the  density  of  the 
dilute  alcohol  produced  by  the  fermentation.  The  strength  of  this  can 
be  ascertained  by  reference  to  the  tables,  and  the  weight  so  arrived 
at  can  be  calculated  into  its  equivalent  of  sucrose  or  maltose  by  the 
factor  1.96,  or  into  glucose  by  the  factor  2.02.  The  dextrose  may 
also  be  deduced  by  calculating  0.219%  for  each  degree  of  gravity  lost. 

It  is  evident  that  the  last-described  method  can  be  advantageously 
employed  as  a  check  on  the  distillation  process. 

Instead  of  estimating  the  sugar  from  the  sp.  gr.  of  the  solution 
before  and  after  fermentation,  equal  volumes  of  the  original  and  the 
filtered  fermented  liquids  may  be  evaporated  to  dryness,  and  the 
quantity  of  sugar  deduced  from  the  loss  of  weight.  An  addition  of  5 
%  to  the  amount  of  sugar  thus  found  should  be  made  as  a  cor- 
rection for  the  succinic  acid  and  glycerol  which  are  produced  by  the 
fermentation  and  remain  in  the  residue  from  the  fermented  liquid. 
When  the  quantity  of  sugar  is  small,  this  method  is  preferable  to  an  esti- 
mate based  on  the  gravity  lost. 

In  determining  sugar  by  fermentation  with  yeast  it  is  desirable  to 
add  to  the  solution  a  little  yeast-ash  or  sodium  phosphate  and  potas- 
sium nitrate,  so  as  to  furnish  the  yeast  with  the  inorganic  elements 
requisite  for  its  nutrition. 

The  estimation  of  sugar  by  fermentation  with  yeast  is  occasion- 
ally very  valuable,  and  when  the  process  is  carefully  conducted  the 
results  are  fairly  accurate. 

The  application  of  pure  culture  yeasts  to  the  separation  of  different 
sugars  promises  valuable  results.  The  sugar  not  attacked  by  the 
yeast  in  a  mixture  of  fermentable  and  unfermentable  carbohydrate 
can  be  estimated  accurately;  the  estimation  of  the  quantity  of  the 
fermented  sugar  from  the  carbon  dioxide  lost  does  not  always  give 
trustworthy  results. 

The  quantitative  fermentation  of  sugars  requires  from  6  to  7  days  or" 
longer  if  maltose  is  to  be  fermented  in  presence  of  dextrin.  The  use  of 
yeast  affords  practically  the  only  accurate  method  of  separating  dextrose 
from  maltose  in  the  analysis  of  starch  syrups. 


GROUP-TESTS    FOR    SUGARS. 


3OI 


.so 

U.       O 

gw 
Qu 


0,  £ 


2    .  2 
2^2 

W  ""*   X 

p    p 


1 


o"o 

If5" 

U 


a  « 


I   3g* 

Iilal 

R       H  fc»I 

p  III 


Mi  M 

o  o  ^  5 

^Si 

lill 


Saccha 
oxalic 


^d^d  § 

,«    3    ^^   3  -5 
cj  M  13    rt  O 

•*-»         0)  *^  O 


•3      2  v    • 

2>,?I1 
si's0-! 

•H   *->   -H    ^    h 


llow  crys- 
lline osa- 
ne  soluble 
hot  water. 


&s-'    ?3H    *8| 


W    04    CJ 

vj"  u  rt 


a  o.a 

•i:si 

S  S  » 


<u  «*H  T3 

irilililifHS 

i^rs  ir^ 


o    a 


H 
an 
and 
sa 


salt. 

Trea 
centr 
rod 


302  SUGARS. 

Recognition  of  the  Principal  Kinds  of  Sugar. — When  a  sugar  has 
been  isolated  in  a  condition  of  tolerable  purity,  it  may  be  recognised 
by  the  special  characters  described  in  the  tables  of  properties  on  page 
301.  The  detection  or  identification  of  a  sugar  by  its  reactions  is 
greatly  simplified  by  applying  the  tests  in  a  systematic  manner. 

All  the  substances  referred  to  in  the  table  are  optically  active. 
Honce  it  is  not  possible  to  have  an  inactive  solution  containing  a 
notable  quantity  of  one  of  the  above  sugars.  If  laevulose  is  present, 
together  with  a  certain  proportion  of  one  of  the  other  sugars,  the  solu- 
tion may  exhibit  no  rotation  at  a  certain  temperature,  but  would  do 
so  on  heating  or  cooling,  owing  to  the  marked  influence  of  tempera- 
ture on  the  reduced  optical  activity  of  laevulose. 

Laevulose  always  occurs  in  practice  in  presence  of  more  or  less 
dextrose,  and  in  such  cases  is  most  easily  detected  by  the  change  in  the 
optical  activity  of  the  solution  on  heating.  Other  distinctions  be- 
tween laevulose  and  dextrose  will  be  found  under  " Laevulose." 

Milk  sugar  is  only  met  with  in  products  derived  from  milk.  It  is 
peculiar  in  having  its  optical  activity  and  cupric  reducing  power  in- 
creased by  treatment  with  dilute  acid,  and  in  yielding  mucic  acid  on 
oxidation  with  nitric  acid.  Physically  it  is  distinguished  from  other 
sugars  by  its  crystalline  form  and  sparing  solubility  in  cold  water. 

Cane  sugar  is  well  characterised  by  its  behaviour  towards  invertase 
in  addition  to  tests  i,  3,  4,  5,  and  6. 

Maltose  when  unmixed  with  dextrose  is  distinguished  from  the  latter 
by  reactions  2  and  5,  but  if  dextrose  be  also  present  only  a  quantitative 
application  of  tests  3,  4,  5,  and  6  will  suffice  for  the  detection  of  maltose. 

Dextrin,  which  often  occurs  together  with  maltose,  may  be  detected 
in  mixtures  of  the  two  by  gradually  adding  a  large  excess  of  strong 
alcohol,  when  it  is  precipitated  in  flocks  which  often  adhere  to  the 
sides  of  the  beaker  as  a  gummy  mass.  Dextrin  is  said  to  be  unaffected 
in  its  optical  activity  by  boiling  with  a  concentrated  alkaline  solution  of 
mercuric  cyanide,  by  which  treatment  maltose  and  dextrose  are  oxidised 
and  destroyed. 

Numerous  colour  reactions  for  the  identification  of  the  more  im- 
portant sugars  in  carbohydrate  mixtures  have  been  described,  most  of 
which  have  the  disadvantage  that  they  are  not  very  characteristic. 
A  discussion  of  these  hardly  enters  into  the  subject  of  commercial 
analysis.  Fenton's  test  for  carbohydrates  (Proc.  Camb.  Phil.  Soc.,  1906, 
14,  24)  which  involves  the  formation  of  w-bromomethylfurfuralde- 


ESTIMATION    OF    SUGARS. 


303 


hyde,  the  merest  trace  of  which  may  be  detected,  is  of  extreme  deli- 
cacy. A  small  quantity  of  the  sample  is  moistened  with  water,  mixed 
with  a  few  drops  of  phosphorus  tribromide  dissolved  in  toluene,  and 
heated  on  a  water-bath  at  90-100°  till  it  has  become  dark-coloured. 
It  is  then  cooled,  stirred  with  a  few  drops  of  ethyl  malonate  in  a  little 
alcohol  and  made  alkaline  by  alcoholic  potassium  hydroxide.  A  char- 
acteristic blue  fluorescence  is  obtained  on  dilution  with  much  water. 

w-Dinitrobenzene  gives  a  violet  co  ouration  with  aldoses  and  ketoses 
in  moderately  alkaline  solution.  This  appears  usually  after  15  minutes 
in  a  i  %  sugar  solution. 

For  the  estimation  of  sugars  in  admixture  the  cupric  reducing 
power  (K)  and  specific  rotatory  power  [a]D  should  be  ascertained  under 
the  following  circumstances : 

In  the  original  solution  of  known  concentration. 

In  the  solution  after  treatment  with  invertase. 

In  the  solution  after  heating  for  some  hours  with  dilute  sulphuric  acid. 

The  following  table  shows  the  relative  cupiic  reducing  power  (K) 
(estimated  gravimetrically)  of  the  principal  sugars,  that  of  dextrose 
being  taken  as  100;  and  the  specific  rotatory  power  [a]D  of  the  solu- 
tions of  the  original  substances,  and  of  the  inverted  solutions  there- 
of, corrected  for  increase  in  volume.  The  values  given  are  in  all 
cases  calculated  for  the  anhydrous  substance,  and  the  volume  of  the  solu- 
tion is  assumed  to  remain  unchanged,  any  dilution  being  duly  allowed 
for. 


Dex- 
trose 

Laevu- 
lose 

Milk 
sugar 

Maltose 

Cane 
sugar 

Dextrin 

Cupric  Oxide  Reducing  Power 

a.  Of  original  solution. 

100 

100 

67.8 

62 

0 

0 

b.  After  treatment    with  inver- 

tase, 

100 

100 

67.8 

62 

105.3 

0 

c.  After  heating  with  acid. 

100 

100 

97-7 

105.3 

105.3 

in  .  i 

Specific    Rotatory     Power    (for 

Sodium  ray  =  [a]D  )  ; 

a.  For  original  solution, 

+  52.7        —98.8       +55-8        +139-2 

+66.5 

+  198 

b.  After  treatment  with    inver- 

tase, 

+  52.7        —  98.8       +55.8        +139.2 

—24.3      +198 

c.  After  heating  with  acid, 


+52.7        —  98.8       +71.0        +   55.0      —  24.3      +   58.5 


It  must  be  borne  in  mind  that  the  figures  representing  the  cupric 
reducing  powers  after  treatment  with  invertase  or  dilute  acid  are 
not  the  values  of  K  for  the  original  weights  of  substance,  but  for  the 
products  of  the  inversion. 


304  SUGARS. 

In  determining  the  values  of  K  and  [a]D,  it  is  necessary  to  know  the 
amount  of  sugar  employed  in  the  operation.  This  is  best  ascertained 
by  evaporating  to  dryness  a  known  measure  of  the  solution  employed 
for  the  analysis,  but  in  some  respects  there  is  an  advantage  in 
calculating  the  strength  of  the  solution  from  the  sp.  gr.  The  concen- 
tration of  solutions  of  pure  cane  sugar  can  be  accurately  ascertained 
by  dividing  the  excess  of  sp.  gr.  over  that  of  water  by  3.86,  as  described 
on  page  290,  but  this  divisor  is  not  strictly  accurate  for  solutions  of 
other  carbohydrates.  In  practice  it  is  sometimes  very  convenient  to 
follow  the  practice  of  Brown  and  Heron  (Jour.  Cheni.  Soc.,  1879,  35, 
569),  and  assume  all  solutions  of  carbohydrates  to  have  the  sp.  gr.  of 
cane-sugar  solutions  of  the  same  strength,  using  appropriately  modified 
figures  to  express  the  values  of  K  and  [a]D.  As  the  true  sp.  gr.  of  a 
solution  of  dextrin  containing  10  grin,  of  the  dry  solid  in  100  c.c.  meas- 
ure is  1039.4  ,  the  value  of  MD3.g6  will  be  198  x  - — =  +  194. 

The  following  is  a  description  in  outline  of  the  mode  of  procedure 
which  should  be  adopted  in  the  application  of  the  foregoing  principles 
to  the  analysis  of  one  of  the  most  complicated  saccharine  mixtures 
likely  to  be  met  with  in  practice.  It  assumes  the  presence  in  admix- 
ture of  dextrose,  laevulose,  sucrose,  maltose,  dextrin,  and  gallisin,  to- 
gether with  water  and  mineral  matter.  Such  a  mixture  would  be 
represented  by  honey  which  had  been  adulterated  both  with  cane  sugar 
and  glucose  syrup  (see  page  385). 

The  total  solids  are  estimated  by  evaporating  a  known  measure  of 
the  solution  to  dryness  in  a  flat  dish.  On  deducting  the  ash  left  on  ig- 
niting the  residue  the  amount  of  the  organic  solids  will  be  ascertained. 
The  solids  may  also  be  deduced  from  the  density  of  the  solution  by 
dividing  the  excess  above  1000  by  3.86  (see  p.  290). 

The  dextrin  may  be  precipitated  by  pouring  the  aqueous  solution 
gradually  into  a  large  excess  of  rectified  spirit.  After  standing  till 
the  precipitate  is  completely  settled,  the  liquid  is  poured  off  and  the 
dextrin  estimated  in  the  residue  by  direct  weighing,  or  deduced  from 
the  solution-density  or  optical  activity  of  the  redissolved  residue. 

The  gallisin  may  be  estimated  by  distilling  the  alcoholic  solution 
obtained  in  b,  fermenting  an  aliquot  part  of  the  residual  liquid,  and 
treating  the  filtered  solution  left  after  complete  fermentation  by 
Fehling's  solution. 

The  rotation  due  to  the  sum  of  the  optically  active  bodies  present  is 
ascertained  on  the  clarified  solution  at  15°. 


SACCHARIMETRY.  305 

The  licriilosc  is  estimated  from  the  change  in  the  rotatory  power  of 
the  solution  on  heating. 

The  sucrose  is  estimated  from  the  change  produced  in  the  rotatory 
power  of  the  solution  by  treatment  with  invertase.  The  result  is 
confirmed  by  the  change  in  the  cupric  oxide  reducing  power  of  the 
solution  caused  by  the  action  of  the  invertase. 

The  cupric  reducing  power  of  the  original  solution  is  determined 
gravimetrically  by  Fehling's  solution.  From  the  value  for  K  thus 
obtained  that  due  to  any  gallisin  found  after  fermentation  is  de- 
ducted, and  from  the  remainder -is  subtracted  the  reduction  due  to 
any  laevulose  present.  The  difference  is  the  reducing  powrer  due  to 
the  dextrose  and  maltose.  The  sum  of  their  weights  having  been 
ascertained  by  deducting  the  laevulose,  sucrose,  dextrin,  gallisin,  and 
ash  from  the  total  solids,  the  amounts  of  maltose  may  be  calculated  by 
subtracting  the  value  of  K  for  the  two  bodies  from  the  sum  of  the  per- 
centages of  the  two,  and  dividing  the  difference  by  0.38.  The  maltose 
thus  found  is  subtracted  from  the  sum  when  the  percentage  of  dextrose 
will  be  arrived  at. 

Specific  Rotatory  Power  of  Sugars. — The  principles  used  in 
the  construction  of  polarimeters  are  defined  in  the  Introduction  to 
this  volume.  To  determine  the  specific  rotatory  power  of  a  carbo- 
hydrate the  more  scientific  plan  is  to  use  an  instrument  graduated 
in  circular  degrees  and  observe  the  rotation  caused  by  a  known 
weight  of  the  sugar  dissolved  in  a  known  quantity  of  water;  it  is 
further  necessary  to  know  the  temperature  of  the  solution  and  the 
length  of  the  tube.  The  alternative  method  is  to  make  use  of  an 
instrument  in  which  the  deviation  is  produced  by  a  plate  of  quartz 
i  mm.  in  thickness  for  which  that  strength  of  sucrose  which  will 
produce  the  same  deviation  when  examined  in  a  2-dcm.  tube  is  de- 
termined. Such  instruments  are  usually  graduated  so  that  the  per- 
centage of  sugar  present  in  the  solution  examined  which  contains  the 
normal  weight  of  the  sample  may  be  read  off  directly.  For  a  full 
discussion  of  the  large  amount  of  work  on  this  subject  the  reader  is 
referred  to  special  text-books,  particularly  that  of  Landolt — "Optical 
Rotatory  Power."  f 

The  specific  rotation  of  sugars  is  sensibly  affected  by  the  concentration 
of  the  so  ution  and  not  always  in  the  same  direction.  Thus  strong  solu- 
tions of  sucrose  cause  a  less  deviation  than  the  same  amount  of  sugar 
would  in  more  di  ute  solutions,  while  with  dextrose  the  reverse  is  the  case. 
VOL.  1—20 


306  SUGARS. 

The  approximate  value  of  [a]D  for  a  solution  of  sucrose  containing 
10  grm.  in  100  c.c.  of  liquid  is  +66.5°.     Tollens  gives  the  following 
formulae  for  the  exact  apparent  specific  rotatory  power,  in  which  p 
represents  the  concentration  of  the  sugar. 
Solutions  containing  18  to  69%  sucrose. 
[a]D*>=66.386  +  o.oi5,o35  ^-0,000,3986  p2. 
So  utions  contain  ng  4  —  18%  sucrose. 
[a]D20=66.8io— 0.015,553  ^—0.000,052,462,   p2. 
There  are  very  many  difficulties  in  the  way  of  obtaining  a  constant 
value  for  [a]j,  due  in  part  to  the  fact  that  the  transition  tint  is  not 
a  ray  of  definite  ref rangibility  and  even  differs  with  different  observers . 
The  value  generally  adopted  is    +73.8°  whence  [a]//[a]D  =   i.no 
and  [a]D/[a]y  =  0.9011. 

Brown  and  Millar  (Trans.  Chem.  Soc.,  1897,  71,  73)  give  the  follow- 
ing factors  for  converting  [a]D  into  [a];«: 

Sugar.  Per  cent.    Factor. 

Cane  sugar,  10         i .  107 

Maltose,  10         1.113 

Maltose,  5         i .  1 1 1 

Dextrose,  10         1.115 

Dextrose,  5         i .  1 1 1 

Starch  products,         10         i .  1 1 1 
Starch  products,          5         i.m 

The  following  table  contains  the  most  reliable  observations  of  spe- 
cific rotation  of  the  more  important  species  of  sugar  for  solutions  con- 
taining 10%  or  so  of  the  solid  sugar.     The  optical  properties  of  the 
rarer  sugars  are  shown  in  the  tables  on  pages  287-8. 
Sugar.  [a]D. 

d-Dextrose,         +52.7° 

d-Galactose,       +81° 

d-Laevulose,        —93.8° 

Sucrose,  +66.5° 

Maltose,  +138° 

Lactose,  +52-5° 

Raffinose,  + 104° 

Polarimetric  Estimation  of  Sucrose  in  the  Absence  of  Other 
Substances. — Until  recently,  although  the  general  principles  of 
the  methods  of  optical  saccharimetry  were  well  understood,  each  ob- 


SACCHARIMETRY.  307 

server  modified  the  more  minute  details  of  the  process  to  suit  his 
special  convenience  and  in  consequence  slightly  different  results  were 
habitually  obtained  in  different  countries.  To  obviate  this,  the  Inter- 
national Commission  for  unifying  methods  of  sugar  analysis  was 
called  into  being.  At  the  Paris  meeting  in  1900,  the  normal  tempera- 
ture of  +20°  was  adopted  and  all  measuring  vessels  are  required  to 
be  graduated  in  true  metric  c.c.  at  this  temperature. 

The  preparation  of  the  normal  sugar  solution  is  as  follows:  26 
grm.  of  chemically  pure  dry  sugar,1  weighed  in  air  with  brass 
weights,  are  dissolved  in  water  at  20°  in  a  flask  graduated  to  con- 
tain 100  true  c.c.  (or  26.048  grm.  of  pure  sugar  in  100  Mohr  c.c.) 
the  solution  filled  up  to  the  mark,  well  mixed,  filtered  if  necessary,  and 
polarised  in  a  200  mm.  tube  at  20°  C.  The  apparatus  must  under  these 
conditions  indicate  100  units  on  the  scale,  and  each  scale  division  cor- 
responds to  0.26  grm.  of  sucrose. 

For  laboratories  in  which  temperatures  are  usually  higher  than  20°, 
it  is  permissible  to  graduate  saccharimeters  at  any  suitable  tempera- 
ture under  the  conditions  specified  above,  providing  that  the  analysis 
of  the  sugar  be  made  at  the  same  temperature — that  is,  that  the  volume 
be  completed  and  the  polarizations  made  at  the  temperature  specified. 

For  the  purposes  of  saccharimetry,  it  is  found  convenient  in  practice 
to  employ  a  constant  weight  of  each  sample.  The  weight  to  be  taken 
ranges  from  16.19  to  26.07  grm->  according  to  the  instrument  to  be 
employed,  and  to  a  less  degree  with  each  particular  instrument. 
With  SoleiPs  saccharimeter  the  standard  weight  is  16.350  grm.,  and 
with  other  instruments,  showing  directly  the  percentage-content  of 
real  sugar  in  the  sample,  weights  closely  approximating  to  16.337 
grm.  are  usually  employed.  With  polarimeters  furnished  with  the 
Ventzke2  scale,  however,  the  standard  weight  is  26.048  grm.  altered 
since  1900  to  26.0  grm. 

For  the  assay  of  commercial  sugar,  the  sugar  scale  divisions  are  the 
most  convenient,  but  for  the  estimation  of  the  percentage  content  of  a 
carbohydrate  in  solution  the  use  of  circular  degrees  is  preferable. 

lTo  prepare  pure  sugar,  further  purify  the  purest  commercial  sugar  in  the  following  man- 
ner: Prepare  a  hot  saturated  aqueous  solution,  precipitate  the  sugar  with  absolute  ethyl 
alcohol,  spin  the  sugar  carefully  in  a  small  centrifugal  machine,  and  wash  in  the  latter  with 
absolute  alcohol.  Redissolve  the  sugar  thus  obtained  in  water,  again  precipitate  the  satu- 
rated solution  with  alcohol,  and  wash  as  above.  Dry  the  second  crop  of  crystals  between 
blotting-paper  and  preserve  in  glass  vessels  for  use.  Determine  the  moisture  still  contained 
in  the  sugar  and  take  this  into  account  when  weighing  the  sugar  which  is  to  be  used. 

*In  the  original  Sol eil- Ventzke  instruments  the  scale  was  so  divided  that  a  solution  of 
cane  sugar,  of  a  sp.  gr.  of  i.ioat  17°. 5,  observed  in  a  tube  20  centimeters  in  length,  rotated 
100  divisions.  A  solution  of  sugar  of  the  above  sp.  gr.  is  obtained  by  dissolving  26.048 
grm.  in  water  and  diluting  the  liquid  to  100  c.c. 


3o8 


SUGARS. 


The  following  table  comparing  the  various   instruments   will   be 
found  useful: 


Instrument 

Normal 
weight  of 
sugar 

i  Sugar  scale 
division  = 
Angular 
degrees  D 

i  Angular 
degree  D  = 
divisions 

German     ir 
Haensch, 
Soleil-Dubo 
Laurent..  .  . 
Wild  

struments,     Schmidt     and 
Ventzke,  Scheibler,  etc  .  .  . 

SCQ 

26  .  048 
16.35 
16.  27 

10.  0 

0.3468 
o.  2175 
o.  2167 
Q.I331 

2-8835 

4-597 
4.6154 

0-7551 

It  is  now  recognised  that  a  rise  of  temperature  occasions  a  lowering 
of  the  rotation  of  sucrose.  To  correct  for  this  Watts  and  Tempany 
give  the  formula-polarisation  — 0.00031  /N  where  N  is  the  Ventzke 
scale  reading  and  /  the  difference  between  the  temperature  of  obser- 
vation and  that  at  which  the  instrument  was  standardised. 

The  following  precise  instructions  regarding  the  care  of  the  instru- 
ments used  are  given  by  the  A.  O.  A.  C.: 

In  effecting  the  polarisation  of  substances  containing  sugar  employ 
only  half-shade  or  triple  field  instruments. 

During  the  observation  keep  the  apparatus  in  a  fixed  position  and  so 
far  removed  from  the  source  of  light  that  the  polarisation  nicol  is  not 
warmed.  Make  several  readings  and  take  the  mean  thereof,  but  no 
one  reading  may  be  neglected. 

In  making' a  polarisation  use  the  whole  normal  weight  for  100  c.c.,  or 
a  multiple  thereof  for  any  corresponding  volume. 

As  clarifying  and  decolourising  agents  use  either  of  basic  lead, 
acetate,  alumina  cream,  or  concentrated  solution  of  alum.  Boneblack 
and  similar  decolourising  agents  are  to  be  excluded. 

After  bringing  the  solution  exactly  to  the  mark  at  the  proper  tem- 
perature and  after  wiping  out  the  neck  of  the  flask  with  filter-paper, 
pour  all  of  the  well-shaken  clarified  sugar  solution  on  a  rapidly  acting 
filter.  Reject  the  first  portions  of  the  filtrate  and  use  the  rest,  which 
must  be  perfectly  clear  for  polarization. 

PREPARATION    OF    REAGENTS. 

(i)  Basic  Lead  Acetate  Solution. — Prepare  by  boiling  430  grm. 
of  normal  lead  acetate,  130  grm.  of  litharge,  and  1,000  c.c.  of  water  for 


SACCHARIMETRY.  309 

half  an  hour.  Allow  the  mixture  to  cool  and  settle  and  dilute  the  super- 
natant liquid  to  1.25  sp.  gr.  with  recently  boiled  water.  Solid  basic 
lead  acetate  may  be  substituted  for  the  normal  salt  and  litharge  in  the 
preparation  of  the  solution. 

(2)  Alumina  Cream. — Prepare  a  cold  saturated  solution  of  alum  in 
water  and  divide  into  two  unequal  portions.  Add  a  slight  excess  of 
ammonia  to  the  larger  portion  and  then  add  by  degrees  the  remaining 
alum  solution  until  a  faintly  acid  reaction  is  secured. 

Preparation  of  the  Solution  of  Sugar  for  the  Polarimeter. — 
The  standard  quantity  of  the  sample  is  weighed  out,  introduced  into 
a  100  c.c.  flask  and  dissolved  in  about  50  c.c.  of  water.  If  this  solution 
be  clear  and  colourless  it  is  diluted  to  100  c.c.  and  introduced  into  the 
tube  of  the  polarimeter.  If  the  liquid  is  coloured  to  any  notable 
extent,  as  is  usually  the  case  with  commercial  sugars,  it  has  first  to 
be  decolourised.  This  clarification  may  be  effected  by  means  of 
either  of  the  reagents  noted  above.  It  is  advisable  to  reject 
the  first  runnings.  The  following  method  of  clarification  is  very  effi- 
cacious even  under  extremely  unfavorable  conditions:  The  normal 
quantity  of  sugar  is  dissolved  in  about  50  c.c.  of  water  in  a  flask  hold- 
ing 100  c.c.  According  to  the  quality  of  the  sample  the  solution  will  be 
(i)  colourless  but  cloudy,  (2)  yellow,  (3)  brown,  or  (4)  almost  black. 
In  the  first  case,  add  about  3  c.c.  alumina  cream  and  one  drop  of  basic 
lead  acetate  solution.  In  the  second  case,  the  same  volume  of  a 
lumina  cream  may  be  used,  but  the  lead  solution  increased  to  3  or  5 
drops.  In  the  third  or  fourth  case  add  about  2  c.c.  of  a  10  %  solution 
of  sodium  sulphite,  and  then  the  lead  solution  gradually,  with  constant 
shaking,  till  no  further  precipitate  is  produced.  Whichever  mode  of 
clarification  is  adopted,  the  liquid  is  well  agitated  and  allowed. to 
stand  at  rest  for  a  few  minutes,  to  insure  the  complete  separation  of 
any  precipitate.  The  flask  is  then  filled  nearly  to  the  mark  with  water, 
and  the  froth  allowed  to  rise  to  the  surface,  when  it  is  destroyed  by 
the  cautious  addition  of  a  few  drops  of  spirit  or  a  single  drop  of  ether. 
Water  is  then  added  exactly  to  the  mark,  the  contents  of  the  flask 
thoroughly  mixed  by  agitation,  and  the  liquid  filtered  through  a  dry 
filter. 

The  validity  of  the  simple  direct  polarimetric  reading  of  a  standard 
solution  of  a  commercial  sugar  as  a  measure  of  the  actual  amount  of 
sucrose  contained  in  it  is  the  most  vexed  question1  of  industrial  sugar 

^difference  of  0.2  or  0.3  per  cent,  on  an  importation  of  5,000  or  10,000  tons  obviously 
runs  into  large  figures. 


310  SUGARS. 

chemistry  and  the  attention  of  chemists  has  been  largely  directed 
towards  securing  uniformity  in  the  process.  It  is  out  of  the  question 
here  to  do  more  than  briefly  refer  to  some  of  the  difficulties,  especially 
as  much  that  has  been  written  on  the  matter  is  of  a  controversial  nature. 

Clarification  with  basic  lead  acetate  is  productive  of  error  owing  to 
the  volume  occupied  by  the  precipitate.  Further1  excessive  amounts 
exercise  an  appreciable  effect  on  the  optical  activity  and  reducing  power 
of  any  invert  sugar  contained  in  the  sugar  solution.2 

The  use  of  anhydrous  basic  lead  acetate  as  proposed  by  Home 
(/.  Amer.  Chem.  Soc.,  1904,  26,  186)  enables  these  errors  to  be  over- 
come. Excess  is  easily  avoided  since  each  particle  of  the  powder 
added  produces  a  precipitation  and  no  more  is  added  when  the  pre- 
cipitation begins  to  be  slight.  In  such  cases,  the  filtrate  is  free  from 
lead  and  clarification  involves  no  appreciable  error.  This  appears  to  be 
the  most  convenient  and  accurate  method  of  clarifying  sugar  solutions. 

In  the  case  of  low-grade  products  Watts  and  Tempany  proceed  as 
follows: 

A  double  normal  weight  is  dissolved  in  100  c.c.  partially  clarified  with 
dry  basic  lead  acetate  and  the  solution  filtered.  50  c.c.  of  the  dark 
coloured  filtrate  are  saturated  with  sulphur  dioxide  and  the  lead  pre- 
cipitated as  sulphite.  The  solution  is  diluted  to  100  c.c.  and  filtered 
when  a  bright  lemon-yellow  filtrate  is  usually  obtained. 

Another  mode  of  clarification  is  as  follows:  Solutions  of  alum  or 
aluminum  sulphate  and  of  basic  lead  acetate  are  prepared  of  equiv- 
alent strengths,  so  that  on  mixing  equal  volumes  and  filtering  no 
sulphate  remains  in  solution.  To  the  solution  of  sugar  5  c.c.  of  each 
of  these  liquids  are  added,  the  mixture  shaken,  made  up  to  100  c.c..  and 
passed  through  a  dry  filter. 

Some  exceptionally  dark  cane  sugars,  and  most  beet-root  molasses 
are  not  sufficiently  decolourised  by  either  of  the  above  methods.  In 
such  cases  a  double  normal  quantity  should  be  weighed  out,  and  the 
solution  clarified  by  sodium  sulphite  and  basic-lead  solution,  as  before 
described,  a  rather  larger  quantity  of  the  latter  liquid  being  employed. 
The  solution  is  made  up  accurately  to  100  c.c.,  filtered,  and  50  c.c.  of 
the  filtrate  treated  with  a  saturated  solution  of  sulphurous  acid3  until 

JThe  question  is  fully  discussed  by  Watts  and  Tempany ,  J.  Soc.  Chem.  Ind. ,  1907,27,53. 

2Formaldehyde,  which  is  used  in  preserving  saccharine  solutions  in  sugar  mills,  if  present 
in  greater  quantity  than  i  c.c.  of  formalin  per  100  c.c.  of  sugar  solution,  appreciably  increases 
the  rotation.  See  Norris,  Bulletin  23,  of  Agriculture  and  Chemistry,  Sandwich  Islands, 
Feb.  19,  1908. 

3Instead  of  employing  a  saturated  solution  of  sulphurous  acid  it  is  convenient  to  bubble 
through  the  liquid  a  little  sulphur  dioxide. 


SACCHARIMETRY.  31! 

the  liquid  smells  strongly  of  the  gas.  About  2  grm.  of  purified  animal 
charcoal1  are  then  added,  the  liquid  well  shaken,  made  up  exactly  to 
100  c.c.,  and  filtered.  By  proceeding  in  this  manner,  a  perfectly  colour- 
less or  lemon-yellow  solution  may  be  obtained  from  the  worst  samples.2 

Careful  experiments  as  to  the  effect  of  basic  lead  acetate  on  the  opti- 
cal rotation  of  sucrose  have  been  made  by  Bates  and  Blake  (/.  Amer. 
Chem.  Soc.,  1907,  29,  286)  who  find  that  a  diminished  polariscope 
reading  is  first  caused  and  that  further  addition  of  the  reagent  pro- 
duces a  continuous  rise  in  the  rotation.  This,  they  consider,  is 
probably  due  to  the  formation  of  soluble  lead  saccharates  having  rota- 
tory powers  different  from  that  of  sucrose. 

Pellet  (Bull.Soc.  Chim.Sucr.  Diot.,  1906,  23,  1466-1471)  points  out 
that  in  clarifying  sugar  solutions  with  basic  lead  acetate  two  sources  of 
error  are  introduced:  (i)  The  volume  occupied  by  the  precipitate 
causes  the  true  concentration  of  the  sugar  solution  to  be  greater  than 
the  apparent,  thereby  increasing  the  reading.  (2)  The  precipitate 
retains  a  quantity  of  the  sugar  mechanically,  thereby  reducing  the  read- 
ing. Pellet's  experiments  show  that  these  errors  compensate  each  other 
and  there  is  no  necessity  to  make  any  correction. 

To  remove  excess  of  lead  from  solutions  clarified  with  lead  acetate, 
anhydrous  sodium  carbonate  or  sodium  sulphate  is  frequently  used. 
A  solution  of  double  normal  potassium  oxalate  (184. 4  grm.  in  1000  c.c.) 
is  recommended  by  Sawyer  (/.  Amer.  Chem.Soc.,  1904,  26, 1631).  One 
hundred  c.c.  are  added  to  the  clarified  solution  which  is  filtered  after 
15  minutes.  The  precipitate  is  granular  and  easily  filtered  and  the 
oxalate  does  not  interfere  with  the  polarisation. 

When  basic  lead  acetate  is  used  with  solutions  containing  laevulose  the 
laevulose  lead  compound  must  be  destroyed  by  rendering  the  filtrate  acid. 

Basic  lead  acetate  is  not  suitable  for  clarifying  invert  sugar  products 
containing  salts  which  yield  insoluble  compounds  with  lead  as  such 
precipitates  carry  down  a  certain  amount  of  laevulose.  Schrefeld 
(2.  Ver.  dent.  Zuckerind,  1908,  947)  recommends  the  use  of  normal 
lead  acetate  and  obtains  fairly  accurate  results  in  the  case  of  mo- 
lasses. 

JThis  is  prepared  by  boiling  i  pound  of  freshly  ground  bone-charcoal  in  half  a  gallon  of 
common  yellow  hydrochloric  acid  diluted  with  one  gallon  of  water.  The  liquid  is  filtered 
through  a  linen  bag,  and  the  residue  washed  with  hot  water  till  free  from  acid,  dried  and 
ignited  to  full  redness  in  a  closed  crucible.  It  is  bottled  while  still  warm,  and  kept  carefully 
dry. 

2See  the  articles  on  analysis  of  beet-root  juice  and  molasses  for  precautions  necessary  for 
the  removal  of  foreign  optically  active  bodies  from  these  substances.  Watts  and  Tempany 
(/.  Soc.  Chem.  Ind.,  1907,  27,  53.)  consider  this  method  to  be  liable  to  serious  errors  by 
reason  of  the  precipitate  volumes. 


312  SUGARS. 

To  correct  for  the  volume  of  a  precipitate,  Scheibler's  method  of 
dissolving  normal  weights  of  the  sample  in  100  and  200  c.c.  may 
be  used.  The  true  reading  is  obtained  by  dividing  the  product  of 
the  two  readings  by  their  difference. 

Solutions  of  beet  sugar  clarified  electrically  yield  higher  results  on 
polarisation  than  when  clarified  by  basic  lead  acetate,  owing  possibly 
to  the  presence  of  asparagine;  this  is  obviated  by  the  addition  of  acetic 
acid.  F.  G.  Wiechmann  (Z.  Ver.  deutsch.  Zukerind.,  1906,  1056) 
recommends  the  following  method  of  working: 

26  grm.  of  sucrose  are  dissolved  in  100  c.c.  water  at  20°  and  about 
35  c.c.  are  introduced  into  each  of  the  two  compartments  of  an  elec- 
trolytic cell,  having  a  parchment  diaphragm  and  lead  electrodes.  A 
current  of  0.25  ampere  is  passed  for  five  minutes,  the  anode  liquid 
filtered,  mixed  with  10%  of  its  volume  of  an  8%  solution  of  acetic 
acid  and  polarised.  The  reading  is  increased  by  10%  to  compensate 
for  the  dilution  caused  by  the  acetic  acid. 

Sucrose  in  presence  of  glucose  in  raw  sugar,  molasses,  etc.  Cler- 
get's  Process. 

A  solution  of  cane  sugar  which,  before  inversion,  causes  a  deviation 
of  100  divisions  to  the  right,  after  inversion  has  a  laevorotatory  power 
of  39  divisions  at  10°.  The  change  is  consequently  equivalent  to  a 
rotation  of  139  divisions.  .  Owing  to  the  diminished  optical  power 
of  laevulose  at  higher  temperatures,  this  change  is  less  the  higher  the 
temperature  at  which  it  is  observed.  At  o°  the  change  by  inversion 
equals  144  divisions;  in  general  the  value  at  t°  is  given  by  the  equation  : 

D   =   144   --  t/2. 

By  polarising  a  solution  before  and  after  inversion  the  change  in 
the  polarimetric  reading  due  to  the  hydrolysis  of  the  cane  sugar  present 
is  found  and  if  C  be  that  part  of  the  rotation  produced  by  the  unin- 
verted  liquid  which  is  really  due  to  the  cane  sugar  contained  in  it 

I0°  D 


144  —  1/2 

Adopting  the  International  Commission  methods  when  the  polari- 
sation before  and  after  inversion  is  taken  at  20°,  and  the  normal 
weight  is  26  grms. 

C  =     I0°  D 
132.66 


SACCHARIMETRY.  313 

which  at  a  temperature  /°  C.  becomes 

100  D. 
142.66  -  /  2 

The  (official  in  the  United  States)  method  of  inversion  (International 
Commission)  is  as  follows:  Take  50  c.c.  of  the  normal  sugar  solution 
made  up  in  the  manner  already  described  and  freed  from  lead  by 
treating  with  anhydrous  sodium  carbonate  or  sodium  sulphate,  place 
in  a  100  c.c.  flask,  and  add  25  c.c.  of  water.  Then  add,  little  by  little, 
while  rotating  the  flask,  5  c.c.  of  hydrochloric  acid,  containing  38.8  % 
of  the  acid  (sp.  gr.  1.188).  Heat  the  flask  after  mixing  in  a  water- 
bath  which  is  at  70°.  The  temperature  of  the  solution  in  the  flask 
should  reach  67°  to  69°  in  two  and  one-half  to  three  minutes.  Main- 
tain a  temperature  of  as  nearly  69°  C.  as  possible  during  7  to  7  and  one- 
half  minutes,  making  a  total  time  of  heating  of  ten  minutes.  Remove 
the  flask  and  cool  the  contents  rapidly  to  20°  and  dilute  to  100  c.c. 
Examine  this  solution  in  a  tube  provided  with  a  lateral  branch  and  a 
water  'jacket,  passing  a  current  of  water  around  the  tube  to  maintain 
a  temperature  of  20°. 

The  inversion  may  also  be  accomplished  as  follows:  To  50  c.c.  of 
the  clarified  solution,  freed  from  lead,  add  5  c.c.  of  a  38.8%  solution 
of  hydrochloric  acid  and  set  aside  during  a  period  of  24  hours  at  a 
temperature  not  below  20°;  or  if  the  temperature  be  above  25°  set 
aside  for  ten  hours.  Make  up  to  100  c.c.  at  20°  and  polarise  at 
that  temperature.  This  reading  must  be  multiplied  by  two,  which 
gives  the  invert  reading.  In  case  it  is  necessary  to  work  at  a  tem- 
perature other  than  20°  which  is  allowable  within  narrow  limits,  the 
volumes  must  be  completed  and  both  direct  and  invert  polarisations 
must  be  made  at  exactly  the  same  temperature. 

Estimation  of  Cane  Sugar  in  Presence  of  Raffinose. — The 
high  dextrorotatory  sugar,  raffinose,  often  occurs  in  beet  molasses 
and  products.  The  Clerget  method  is  only  available  when  not  more 
than  one  other  optically  active  substance  is  present  besides  sucrose. 

The  normal  weight  (26  grm.)  of  raffinose  anhydride  in  100  c.c. 
water  has  a  rotation  of  +185.2°  at  20°  in  a  200  mm.  tube  before  and 
+  94.9°  after  inversion.1 

0.5188  P-I 
S=       0.8454 

1  Citric  acid  or  a  weak  mineral  acid  should  be  used  for  inversion  to  avoid  hydrolysing 
the  melibiose  section  of  raffinose. 


314  SUGARS. 

where  S  =  the  amount  of  sucrose,  P  is  the  polarisation  before  and  I 
that  after  inversion. 

p g 

R   (the  amount  of  raffinose)    = 


1.852 

When  invert  sugar  is  also  present  it  is  necessary  to  determine  the  cupric 
reducing  power  of  the  original  and  the  inverted  solution  in  addition  to 
the  above  polarisations. 

To  detect  rafnnose  in  presence  of  sucrose,  Neuberg  and  Marx 
(Zeit.  Ver.  deut.  Zuckerind.,  1907,  453)  make  use  of  the  formation 
of  cupric  reducing  sugars  by  the  action  of  emulsin  on  raffinose,  this 
enzyme  being  without  action  on  cane  sugar.  The  presence  of  reduc- 
ing sugars  or  of  glucosides  which  are  attacked  by  emulsin  prevents  the 
application  of  the  test. 

The  Clerget  method  is  applicable  to  the  estimation  of  cane  sugar  only 
so  long  as  other  sugars,  inulins,  starches  and  glucosides,  which  are  also 
inverted  by  acids,  are  not  present.  In  such  cases  invertase  may  be 
used  to  effect  hydrolysis. 

Preparation  of  Invertase. — Invertase  is  a  soluble  enzyme  present 
in  yeast  and  very  widely  distributed  in  plants.  It  has  the  property 
of  rapidly  and  completely  effecting  the  transformation  of  cane  sugar 
into  invert  sugar  but  is  entirely  without  action  on  dextrose,  laevulose, 
maltose  or  lactose.  Indeed,  the  only  other  substances  which  are 
hydrolysed  by  invertase  are  trisaccharides  like  raffinose  and  sentianose 
which  contain  cane  sugar  in  their  molecule. 

Invertase  is  most  conveniently  prepared  as  follows.  Dry  pressed 
yeast  is  crumbled  as  finely  as  possible  and  spread  out  in  a  thin  layer 
on  a  sheet  of  porous  paper  in  a  dry,  airy  place;  in  the  course  of  a 
day  or  two  it  dries  to  a  light  friable  powder.  When  perfectly  dry, 
it  may  be  bottled  and  kept  indefinitely.  5  grm.  of  this  are  shaken 
for  an  hour  with  100  c.c.  of  water  containing  0.5  c.c.  of  toluene  and 
filtered  bright.  A  few  c.c.  of  this  solution  are  added  to  the  sac- 
charine solution  under  examination,  a  little  toluene  is  added  and  the 
mixture  incubated  in  a  corked  vessel  preferably  at  a  raised  tempera- 
ture— 37  to  50°— for  a  few  hours.  The  determination  of  the  optical 
rotatory  activity  and  reducing  power  in  the  inverted  solution  is  carried 
out  in  the  ordinary  manner,  due  allowance  being  made  for  the 
volume  of  enzyme  solution  added.  This  need  only  be  i  c.c.  or  less 
if  the  amount  of  sucrose  to  be  inverted  is  small  and  at  the  higher 


SACCH  ARIMETRY .  315 

temperature  the  time  required  for  complete  inversion  may  be  less 
than  an  hour. 

Kjeldahl  employed  a  little  fresh  washed  yeast  in  presence  of  thymol 
to  effect  inversion,  fermentation  being  prevented  by  the  antiseptic. 

The  use  of  chloroform  or  ether  as  antiseptics  is  in  general  unde- 
sirable. The  former  must  be  got  rid  of  by  heating  the  liquid  after  in- 
version, as  it  exerts  a  cupric  reducing  action.  Ether,  unless  very 
pure,  may  adversely  affect  the  enzyme.  Invertase  may  also  be 
prepared  by  allowing  brewer's  yeast  to  liquefy — this  takes  a  few  days 
at  37°  C.  The  filtered  liquid  has  a  high  hydrolytic  power.  The 
enzyme  may  be  partially  purified  by  precipitation  with  alcohol  and 
redissolution  of  the  precipitate  in  a  minimum  of  water.  This  extract 
keeps  well  in  presence  of  toluene  in  closed  vessels  in  the  dark. 

If  a  solution  be  inverted  rapidly  it  is  often  advisable  to  add  a  minute 
trace  of  ammonia  before  polarising  to  obviate  the  error  caused  by 
mutarotation  (see  next  paragraph). 

Birotation. — Considerable  confusion  has  in  the  past  been  intro- 
duced into  optical  saccharimetry  owing  to  the  changes  in  rotatory 
power  shown  by  freshly  dissolved  sugars  on  keeping,  a  phenomenon 
known  as  "bi-rotation."  This  change  has  been  shown  by  E.  F.  Arm- 
strong and  T.  M.  Lowry  (Trans.  Chem.  Soc.,  1903,  83,  1305,  1314) 
to  be  due  to  the  mutual  interconversion  in  solution  of  two  isomerides 
of  the  sugar.  The  :<  birotation  "  of  sugars  is  indeed  a  special  case  of  a 
more  general  phenomenon  to  which  Lowry  has  given  the  name  "  muta- 
rotation," to  show  that  its  essential  characteristic  is  a  change  of  rotatory 
powers.  (See  Trans.  Chem.  Soc.,  1899,  75,  212.)  Most  sugars  exist 
in  solution  as  a  mixture  of  two  forms  in  equilibrium.  Thus  in  the  case 
of  glucose  the  anhydrous  solid  is  the  ^-modification  of  high  rotatory 
power  which  persists  as  such  in  the  freshly  made  solution  but  slowly 
passes  over  in  part  into  the  /?-form  of  low  rotatory  power.  The 
change  is  much  accelerated  by  impurities,  particularly  those  of  an 
alkaline  nature.  The  addition  of  a  trace  of  alkali  to  a  freshly  made 
solution  of  glucose  causes  a  sudden  fall  in  the  rotation — this  has  been 
made  use  of  to  identify  the  various  forms  of  this  sugar. 

All  products,  such  as  honeys,  syrups,  etc.,  which  contain  dextrose  or 
other  reducing  sugars  in  the  crystalline  form  or  in  supersaturated  solu- 
tion, exhibit  the  phenomenon  of  birotation.  The  constant  rotation 
only  should  be  employed  in  the  Clerget  formula,  and  to  obtain  this 
the  solutions  prepared  for  direct  polarisation  should  be  allowed  to 


3i6 


SUGARS. 


stand  over  night  before  making  the  reading.  In  case  it  is  desired  to 
make  the  direct  reading  immediately  the  birotation  may  be  destroyed 
by  heating  the  neutral  solution  to  boiling  for  a  few  minutes  or  by  adding 
a  few  drops  of  strong  ammonia  before  completing  the  volume. 

Estimation  of  Sugars  by  Means  of  the  Refractometer. — 
This  method  may  be  used  in  the  same  manner  as  the  sp.  gr.  method, 
over  which  it  has  advantages  in  speed  and  ease  of  manipulation.  The 
most  recent  experience  shows  that  the  refractometric  method  gives 
trustworthy  results  even  with  highly  concentrated  and  very  crude 
syrups.  When  using  the  Pulfrich  instrument,  as  done  by  Stolle  (Zeit. 
Ver.deut.Zuckerind.,  1901,  335,  469),  5  c.c.  of  solution  are  necessary; 
with  the  Abbe  refractometer  a  few  drops  suffice.  Working  with  the 
latter  instrument,  Tolman  and  Smith  (7.  Amer.  Chem.  Soc.,  1906, 
28,  1476)  find  that  for  the  same  concentration  the  index  of  refrac- 
tion is  practically  the  same  for  sucrose,  maltose,  lactose,  dextrose, 
laevulose,  and  commercial  glucose,  but  is  somewhat  higher  for  dextrin. 
The  following  table  gives  the  refractive  index  for  sucrose  solutions 
of  varying  strengths  at  20°.  The  temperature  correction  is  practi- 
cally the  same  as  that  for  sp.  gr. 


Sucrose  % 

Index  of  refrac- 
tion at  20° 

Sucrose  % 

Index  of  refrac- 
tion at  20° 

Sucrose  % 

Index  of  refrac- 
tion at  20° 

i 

•3343 

3i 

.3828 

61 

•  4442 

2 

•3357 

32 

•  3847 

62 

•  4465 

3 

•  3372 

33 

•  3865 

63 

.4488 

4 

•3387- 

34 

•  3883 

64 

•  4511 

I 

•  3402 
.3417 

II 

.3902 
.3921 

Sf 

•4534 
•4557 

7 

•3432 

37 

•  3940 

67 

•  4581 

8 

•  3447 

38 

•3959 

68 

.4605 

9 

.3462 

39 

•  3978 

69 

.4629 

10 

•  3477 

40 

•  3997 

70 

•4653 

ii 

•  3492 

4i 

.4017 

71 

.4677 

12 

.3508 

42 

•  4036 

72 

.4701 

13 

•3524 

43 

.4056 

73 

.4726 

14 

•3539 

44 

.4076 

74 

•  4751 

11 

•3555 
•  3572 

45 
46 

.4096 
•  4117 

11 

•4776 
.4801 

17 

•3588 

47 

•  4137 

77 

.4826 

18 

.3604 

48 

•  4158 

78 

•  4851 

19 

.3621 

49 

•  4179 

79 

.4877 

20 

•  3637 

50 

.4200 

80 

•  4903 

21 

•  3654 

51 

.4221 

81 

.4929 

22 

.3671 

52 

.4242 

82 

•4955 

23 

.3688 

53 

.4263 

83 

.4981 

24 

/•370S 

54 

.4284 

84 

.5007 

25 
26 

•  3722 
•3739 

ii 

•  4306 
.4328 

85 
86 

•5034 
.5061 

27 

•  3756 

57 

•4351 

87 

.5088 

28 

•  3774 

58 

•4373 

88 

•  5115 

29 

•  3792 

59 

•  4396 

89 

.5142 

30 

.3810 

60 

.4419 

90 

•  51/0 

GRAVIMETRIC    ESTIMATION    OF    SUGARS.  317 

Reactions  of  the  Sugars  as  Reducing  Agents. — Most  of  the 
carbohydrates,  with  the  notable  exception  of  cane  sucrose  and  raffinose, 
possess  marked  activity  as  reducing  agents. 

In  hot  alkaline  solution,  the  glucoses  reduce  picric  acid  to  picramic 
acid,  indigotin  to  indigo  white,  and  change  ferricyanides  to  ferrocyan- 
ides.  Bismuth,  mercury,  silver,  platinum,  and  gold  salts  are  reduced  to 
metal  and  ferric  and  cupric  salts  to  ferrous  and  cuprous  compounds 
respectively. 

The  reducing  properties  of  sugars  are  best  manifested  and  measured 
by  their  reaction  on  alkaline  solutions  of  cupric  and  mercuric  salts, 
and  the  processes  in  which  these  are  employed  require  to  be  described 
in  detail. 

In  the  first  place,  the  well-established  standard  processes  will  be 
dealt  with,  followed  by  a  brief  resume  of  the  more  recent  modifications 
of  these  methods,  many  of  which  perhaps  still  require  confirmation 
by  other  workers  before  being  universally  adopted.  They  have  been 
in  many  cases  devised  to  solve  the  difficulties  presented  by  special 
problems. 

Reaction  of  Sugars  with  Cupric  Salts  in  Alkaline  Solution. — 
If  a  solution  of  cupric  sulphate  be  mixed  with  a  sufficient  quantity  of  a 
saccharine  liquid,  no  precipitate  of  copper  hydroxide  is  produced  on 
addition  of  sodium  or  potassium  hydroxide.  The  liquid  becomes 
deep  blue,  but  remains  clear.  On  raising  the  fluid  to  b.  p.  no  visible 
change  occurs  if  the  liquid  contained  sucrose  only,  but,  if  any  form 
of  glucose  is  present,  a  yellow  precipitate  of  cuprous  hydroxide  is 
produced,  which  quickly  turns  to  cuprous  oxide  and  becomes  an 
orange-red.  If  the  glucose  is  present  in  excess  the  blue  of  the 
solution  entirely  disappears.  Instead  of  relying  on  a  saccharine 
substance  for  the  prevention  of  the  precipitation  of  the  cupric 
hydrate  by  the  alkali  it  is  far  better  to  employ  a  tartrate,  as  in 
Fehling's  solution. 

The  reducing  action  of  certain  forms _of  sugar  on  alkaline  solutions 
of  copper  has  been  applied  by  different  chemists  in  many  ways,  the 
precipitated  cuprous  oxide  being  weighed  as  such  by  several,  by  others 
converted  into  metallic  copper  or  cupric  oxide,  and  by  others  redis- 
solved  and  estimated  volumetrically.  Some  operators  make  the  orig- 
inal process  a  volumetric  one.  The  great  majority  of  these  modified 
processes  are  merely  of  historical  interest  and  require  no  detailed 
description. 


318  SUGARS. 

Fehling's  Solution. 

The  alkaline  solution  of  copper  most  commonly  employed  for  the 
determination  of  sugars  is  that  known  as  Fehling's  which  is  essentially 
a  solution  of  copper  sodium  tartrate  containing  a  considerable  quantity 
of  sodium  hydroxide.  (For  the  nature  of  the  salts  existing  in  Feh- 
ling's solution  see  Masson  &  Steele,  Trans.,  1899,  75,  725,  and  Bulln- 
heimer  and  Seitz,  Ber.,  1900,  33,  807.)  It  is  best  prepared  in  the 
following  manner,  known  as  Soxhlet's  modification :  34.64  grm.  weight 
of  pure  crystallised  copper  sulphate  (free  from  iron  and  moisture)  are 
dissolved  in  distilled  water,  and  the  solution  diluted  to  500  c.c.  Seventy1 
grm.  of  sodium  hydroxide  of  good  quality  (not  less  than  97  %  NaOH) 
and  175  grm.  of  recrystallised  potassium  sodium  tartrate  are  dis- 
solved in  about  400  c.c.  of  water  and  the  solution  diluted  to  500  c.c. 
Fehling's  solution  is  prepared  by  carefully  adding  the  copper  sulphate 
solution  to  an  equal  measure  of  the  alkaline  tartrate  solution.  It  may 
be  kept  ready-mixed,  but  should  in  that  case  be  carefully  protected  from 
air  and  light,  as  it  is  apt  to  undergo  changes  which  render  its  indica- 
tions unreliable.  Before  using  it  is  desirable  to  ascertain  its  condition, 
by  diluting  a  quantity  with  an  equal  volume  of  water  and  heating  the 
liquid  to  boiling  for  a  few  minutes.  It  ought  to  remain  perfectly  clear. 
It  is  preferable  to  keep  the  copper  and  tartrate  solutions  separate, 
and  mix  them  in  equal  measures  at  frequent  intervals. 

For  the  detection  of  reducing  sugar  in  clear,  colourless  solution,  all  that 
is  necessary  is  to  neutralise  any  free  acid  and  heat  the  liquid  to  boil- 
ing with  a  little  Fehling's  solution.  If  a  yellow  or  orange-red  turbidity 
or  precipitate  of  cuprous  oxide  be  produced,  a  reducing  sugar,  or  some 
substance  giving  a  similar  reaction,  is  present.  The  glucoses,  and  mal- 
tose, reduce  the  copper  solution  with  facility,  but  sucrose  gives  no 
reaction  until  after  inversion. 

If  the  liquid  is  much  coloured  it  is  difficult  or  impossible  to  recog- 
nise properly  the  reaction  with  Fehling's  solution.  Colouration  of  the 
liquid  is  still  more  objectionable  if  the  sugar  is  to  be  estimated  by  the 
volumetric  process.  In  such  cases  the  sugar  solution  must  be  clarified 
by  one  of  the  methods  employed  for  the  preparation  of  a  solution  for 
the  polarimeter  (see  page  309),  but  if  lead  has  been  employed  it  must 
be  completely  removed  from  the  solution  or  the  results  of  the  test  will 
be  worthless. 

Fehling's  solution  may  be  used  volumetrically  or  gravimetrically. 

^he  A.  O.  A.  C.  uses  50  grm.  of  sodium  hydroxide. 


FEHLING'S  SOLUTION.  319 

Both  methods  are  capable  of  giving  useful  approximate  results,  but  if 
any  high  degree  of  accuracy  be  sought  it  is  essential  that  certain  condi- 
tions of  manipulation  be  strictly  adhered  to. 

As  a  good  approximate  estimation  of  the  amount  of  reducing  sugar 
present  in  a  liquid  is  often  all  that  is  requisite,  it  will  be  convenient 
to  give  methods  by  which  such  results  can  be  readily  obtained,  and 
subsequently  to  describe  the  conditions  which  must  be  observed  if  a 
higher  degree  of  accuracy  be  desired. 

Volumetric  Estimation  of  Reducing  Sugars  by  Fehling's 
Solution. — The  saccharine  solution,  prepared  as  already  described 
and  containing  from  0.5  to  i.o  grm.  of  sugar  per  100  c.c.,  is  placed  in  a 
burette.  Exactly  10  c.c.  of  the  Fehling's  solution  are  measured  into  a 
wide  test-tube  or  small  flask  supported  vertically  by  a  clip.  30  c.c. 
of  water  are  added,  and  a  few  fragments  of  tobacco-pipe  stem  dropped 
in  to  prevent  bumping.  The  liquid  is  heated  to  boiling  by  applying  a 
small  flame,  and  the  sugar  solution  run  in,  2  c.c.  at  a  time,  boiling  be- 
tween each  addition.  When  the  blue  colour  of  the  liquid  has  nearly 
disappeared,  the  sugar  solution  should  be  added  more  cautiously,  but 
it  is  desirable  to  effect  the  titration  as  rapidly  as  possible.  The  end  of 
the  reaction  is  reached  when,  on  removing  the  flame  and  allowing  the 
cuprous  oxide  to  settle,  the  supernatant  fluid  appears  colourless  or  faintly 
yellow  when  viewed  against  a  white  surface.  If  any  doubt  be  felt 
as  to  the  termination  of  the  reaction,  a  few  drops  of  the  liquid  may  be 
filtered  through  a  small  filter  into  a  mixture  of  acetic  acid  and  dilute 
potassium  ferrocyanide  contained  in  a  porcelain  crucible  or  placed 
on  a  white  plate.  If  copper  be  still  present  in  the  liquid,  more  or  less 
brown  colouration  will  be  observed. 

The  results  obtained  by  using  Fehling's  solution  volumetrically  are 
not  generally  so  accurate  as  those  of  the  gravimetric  method.  The 
operation  should  be  quickly  conducted. 

The  following  are  the  weights  of  the  principal  kinds  of  sugar  which, 
it  is  generally  assumed,  will  reduce  10  c.c.  of  Fehling's  solution  prepared 
as  described  on  page  318.  Soxhlet's  figures  are  given  on  page  321. 

10  c.c.  Fehling  solution  =0.0500  grm.  of  dextrose,  laevulose,  or  invert  sugar. 
10  c.c.  Fehling  solution  =0.0475  g1711-  °f  cane  sugar  (after  inversion). 
10  c.c.  Fehling  solution  =0.0678  grm.  of  milk  sugar  (lactose), 
loc.c.  Fehling  solution    =0.0807  grm.  of  maltose. 

In  all  cases  in  which  Fehling's  solution  is  to  be  used  volumetrically 
its  true  oxidising  power  under  the  conditions  of  the  experiment  should 


320  SUGARS. 

be  ascertained  by  actual  trial.    0.0475  grm-  °f  dry  sucrose,  after  being 
inverted  as  described  on  page  313,  and  the  solution  neutralised,  should 
exactly  decolourise  10  c.c.  of  Fehling's  solution. 
The  volumetric  methods  adopted  by  the  A.  O.  A.  C.  are  as  follows : 

(a)  Applicable  to  Invert  Sugar  and  Dextrose. 

Place  10  c.c.  of  the  mixed  copper  reagent  in  a  large  test-tube  and  add 
jo  c.c.  of  distilled  water.  Heat  to  boiling,  and  gradually  add  small 
portions  of  the  solution  of  the  material  to  be  tested  until  the  copper  has 
been  completely  precipitated,  boiling  to  complete  the  reaction  after 
each  addition.  Two  minutes'  boiling  is  required  for  complete  pre- 
cipitation when  the  full  amount  of  sugar  solution  has  been  added  in 
one  portion.  When  the  end  reaction  is  nearly  reached  and  the  amount 
of  sugar  solution  to  be  added  can  no  longer  be  judged  by  the  colour 
of  the  solution,  remove  a  small  portion  of  the  liquid  and  filter  rapidly 
into  a  small  porcelain  crucible  or  on  a  test  plate;  acidify  with  dilute 
acetic  acid,  and  test  for  copper  with  a  dilute  solution  of  potassium  fer- 
rocyanide.  The  sugar  solution  should  be  of  such  strength  as  will  give  a 
burette  reading  of  15  to  20  c.c.  and  the  number  of  successive  additions 
should  be  as  small  as  possible. 

Since  the  factor  of  calculation  varies  with  the  minute  details  of 
manipulation,  every  operator  must  determine  a  factor  for  himself, 
using  a  known  solution  of  a  pure  sample  of  the  sugar  that  he  desires  to 
determine,  and  keeping  the  conditions  the  same  as  those  used  for  the 
determinations. 

Standardise  the  solution  for  invert  sugar  in  the  following  manner: 

Dissolve  4.75  grm.  of  pure  sucrose  in  75  c.c.  of  water,  add  5  c.c. 
of  hydrochloric  acid  (sp.  gr.  1.188),  and  invert  as  under  the  official 
method  for  sucrose,  page  313.  Neutralise  the  acid  exactly  with 
sodium  hydroxide  and  dilute  to  i  liter.  10  c.c.  of  this  solution  con- 
tains 0.050  grm.  of  invert  sugar,  which  should  reduce  10  c.c.  of  the  cop- 
per solution;  the  copper  solution  should  never  be  taken  as  a  standard, 
but  should  be  checked  against  the  sugar.  In  case  this  method  is  used 
for  determining  dextrose,  pure  dextrose  must  be  used  in  standardising 
the  solution. 

(b)  Soxhlet's  Method. 

Make  a  preliminary  titration  to  determine  the  approximate  per  cent- 
age  of  reducing  sugar  in  the  material  under  examination.  Prepare 


VOLUMETRIC    ESTIMATION    OF    SUGARS.  321 

a  solution  which  contains  approximately  i%  of  reducing  sugar. 
Place  in  a  beaker  100  c.c.  of  the  mixed  copper  reagent  and  approxi- 
mately the  amount  of  the  sugar  solution  for  its  complete  reduction. 
Boil  for  two  minutes.  Filter  through  a  folded  filter  and  test  a  portion 
of  the  filtrate  for  copper  by  use  of  acetic  acid  and  potassium  ferro- 
cyanide.  Repeat  the  test,  changing  the  volume  of  sugar  solution,  until 
two  successive  amounts  are  found  which  differ  by  o.i  c.c.,  one  giving 
complete  reduction  and  the  other  leaving  a  small  amount  of  copper 
in  solution.  The  mean  of  these  two  readings  is  taken  as  the  volume 
of  the  solution  required  for  the  complete  precipitation  of  100  c.c.  of  the 
copper  reagent. 

Under  these  conditions  100  c.c.  of  the  mixed  copper  reagent  require 
0.475  grm-  °f  anhydrous  dextrose  or  0.494  grm.  of  invert  sugar  for  com- 
plete reduction.  Calculate  the  percentage  by  the  following  formula: 

V  =  the  volume  of  the  sugar  solution  required  for  the  complete  reduc- 
tion of  100  c.c.  of  the  copper  reagent. 
W  =  the  weight  of  the  sample  in  i  c.c.  of  the  sugar  solution. 

Then  —  =  per  cent,  of  dextrose, 

100X0.494 
or  =  per  cent,  of  invert  sugar. 

The  titration  of  raw  sugars,  malt  worts  and  other  coloured  commer- 
cial products  with  Fehling's  solution,  employing  potassium  ferro- 
cyanide  as  indicator,  is  often  anything  but  an  accurate  method  and  very 
tedious.  When  certain  amino-compounds  are  present  so  much  cu- 
prous oxide  may  be  dissolved  that  it  is  impossible  to  obtain  an  acidified 
filtrate  which  gives  no  colour  with  potassium  ferrocyanide.  Indica- 
tors, which  respond  to  a  minute  trace  of  cupric  salt  and  can  be  em- 
ployed without  filtering  off  a  portion  of  the  assay  liquid,  have  been 
recently  proposed.  E.  F.  Harrison  (Pharm.  Journ.,  1903,  71,  170) 
uses  a  solution  of  starch  and  potassium  iodide  which  when  acidified 
with  acetic  acid  and  brought  into  contact  with  a  cupric  salt  liberates 
iodine  and  blue  is  developed. 

Still  more  satisfactory  is  a  solution  of  ferrous  thiocyanate  as  suggested 

by  A.  R.  Ling,  T.  Rendle  and  G.  C.  Jones  (Analyst,  1905,  30,   182; 

T9o8,  33,  160-170).     When  a  drop  of  this  on  a  white  slab  is  brought 

into  contact  with  a  drop  of  a  solution  of  a  cupric  salt  the  character- 

VOL.  I— 21 


322  SUGARS. 

istic  red  colour  of  ferric  thiocyanate  is  produced.  Ling's  method 
has  been  adopted  by  the  Malt  Analysis  Committee  of  the  Institute 
of  Brewing  (/.  Inst.  Brewing,  1906,  12,  No.  i)  and  is  given  below: 

Preparation  of  the  Indicator. — i  grm.  of  ferrous  ammonium 
sulphate  and  1.5  grm.  of  ammonium  thiocyanate  are  dissolved  in  10  c.c. 
of  water  at  a  moderate  temperature,  say  at  120°  F.,  and  immediately 
cooled;  2.5  c.c.  of  concentrated  hydrochloric  acid  are  then  added. 
The  solution  so  obtained  is  invariably  brownish-red,  due  to  the  presence 
of  ferric  salt,  which  latter  must  be  reduced.  For  this  purpose,  zinc 
dust  is  the  most  satisfactory  reagent,  and  a  mere  trace  is  sufficient  to 
decolourise  the  solution  if  pure  reagents  have  been  employed. 

When  kept  for  some  hours,  the  indicator  redevelops  the  red  by  oxi- 
dation. It  may,  however,  be  decolourised  by  the  addition  of  a  further 
quantity  of  zinc  dust,  but  its  delicacy  is  decreased  after  it  has  been 
decolourised  several  times.  For  practical  purposes  the  indicator 
may  be  too  delicate  and  it  is  recommended  to  prepare  it  the  day 
before  it  is  required  for  use,  as  it  gives  the  best  results  after  the  second 
decolourisation. 

The  method  of  titration  is  as  follows :  Freshly  mixed  Fehling's  solu- 
tion (10  c.c.)  is  accurately  measured  into  a  200  c.c.  boiling  flask  and 
raised  to  boiling.  The  sugar  solution,  which  should  be  adjusted  to  such 
a  strength  that  20  to  30  c.c.  of  it  are  required  to  reduce  10  c.c.  of  Feh- 
ling's solution,  is  then  run  into  the  boiling  liquid  in  small  amounts, 
commencing  with  5  c.c.  After  each  addition  of  sugar  solution,  the  mix- 
ture is  boiled,  the  liquid  being  kept  rotated.  About  a  dozen  drops  of 
the  indicator  are  placed  on  a  porcelain  or  opal  glass  slab  arid  when  it 
is  judged  that  the  precipitation  of  cuprous  oxide  is  complete,  a  drop  of 
the  liquid  is  withdrawn  by  a  clear  glass  rod  or  by  a  capillary  tube  and 
brought  in  contact  with  the  middle  of  a  drop  of  the  indicator  on  the 
slab.  The  test  must  be  carried  out  rapidly.  It  is  also  essential  to 
perform  the  titration  as  rapidly  as  possible,  as  an  atmosphere  of  steam 
is  then  kept  in  the  neck  of  the  flask  and  the  influence  of  atmospheric 
oxygen  is  avoided.  At  the  final  point  the  liquid  is  boiled  for  about 
two  seconds.  As  in  the  ordinary  volumetric  method,  the  first  titration 
may  only  give  approximate  results  and  a  second  or  third  will  then  be 
necessary  to  establish  the  end-point  accurately.  However,  when  the 
operator  has  gained  experience  the  first  titration  is  as  much  to  be  relied 
on  as  succeeding  ones.  One  titration  takes  about  3  minutes.  The 
authors  claim  the  average  error  of  the  method  to  be  about  i  in  300. 


GRAVIMETRIC    ESTIMATION    OF    SUGARS.  323 

Gravimetric  Estimation  of  Reducing  Sugars  by  Fehling's  Solu- 
tion.— This  method  gives  very  accurate  results  provided  the  detal  is 
of  manipulation  are  closely  attended  to. 

Allihn's  Method. — 34.639  grm.  of  crystallized  copper  sulphate  are 
dissolved  in  water  and  diluted  to  500  c.c.  173  grm.  of  sodium  potas- 
sium tartrate  and  125  grm.  of  potassium  hydroxide  are  likewise  dis- 
solved in  water  and  diluted  to  700  c.c.  A  solution  of  the  material  to 
be  examined  is  prepared  so  as  not  to  contain  more  than  i  %  of  dex- 
trose. 30  c.c.  of  each  of  the  reagent  solutions  and  60  c.c.  of  water  are 
placed  in  a  beaker  and  heated  to  boiling;  25  c.c.  of  the  dextrose  solu- 
tion are  added  and  the  boiling  continued  for  exactly  two  minutes. 
The  liquid  is  filtered  immediately  without  dilution  and  the  amount  of 
copper  contained  in  the  cuprous  oxide  determined  by  one  of  the  fol- 
lowing methods: 

(i)   Reduction  in  Hydrogen. 

Filter  the  cuprous  oxide  immediately  through  a  weighed  filtering 
tube  made  of  hard  glass,  using  suction.  Support  the  asbestos  film 
in  the  filtering  tube  with  a  perforated  disk  or  cone  of  platinum  and 
wash  free  from  loose  fibres  before  weighing;  moisten  previous  to  the 
filtration.  Provide  the  tube  with  a  detachable  funnel  during  the  filtra- 
tion, so  that  none  of  the  precipitate  accumulates  near  the  top,  where 
it  could  be  removed  by  the  cork  used  during  the  reduction  of  the 
cuprous  oxide.  Transfer  all  the  precipitate  to  the  filter  and  thoroughly 
wash  with  hot  water,  following  the  water  by  alcohol  and  ether  success- 
ively. After  being  dried,  connect  the  tube  with  an  apparatus  for 
supplying  a  continuous  current  of  dry  hydrogen,  gently  heat  until  the 
cuprous  oxide  is  completely  reduced  to  the  metallic  state,  cool  in  the 
current  of  hydrogen,  and  weigh.  If  preferred,  a  gooch  crucible  may  be 
used  for  the  filtration. 

(2)  Electrolytic  Deposition  from  Sulphuric  Acid  Solution. 

Filter  the  cuprous  oxide  in  a  gooch,  wash  the  beaker  and  precipitate 
thoroughly  with  hot  water  without  any  effort  to  transfer  the  precipitate 
to  the  filter.  Wash  the  asbestos  film  and  the  adhering  cuprous  oxide 
into  the  beaker  by  means  of  hot  dilute  nitric  acid.  After  the  copper 
is  all  in  solution,  refilter  through  a  gooch  with  a  thin  film  of  asbestos 
and  wash  thoroughly  with  hot  water.  Add  10  c.c.  of  dilute  sulphuric 


324  SUGARS. 

acid,  containing  200  c.c.  of  sulphuric  acid  (sp..gr.  1.84)  in  1000  c.c.;  and 
evaporate  the  filtrate  on  the  steam-bath  until  the  copper  salt  has  largely 
crystallized.  Heat  carefully  on  a  hot  plate  or  over  a  piece  of  asbestos 
board  until  the  evolution  of  white  fumes  shows  that  the  excess  of  nitric 
acid  is  removed.  Add  from  8  to  10  drops  of  nitric  acid  (sp.  gr.  1.42) 
and  rinse  into  a  platinum  dish  of  from  100  to  125  c.c.  capacity. 
Precipitate  the  copper  by  electrolysis.  Wash  thoroughly  with  water 
before  breaking  the  current,  remove  the  dish  from  the  circuit,  wash 
with  alcohol  and  ether  successively,  dry  at  about  50°  and  weigh.  If 
preferred,  the  electrolysis  can  be  conducted  in  a  beaker,  the  copper 
being  deposited  upon  a  weighed  platinum  cylinder. 

(3)  Electrolytic  Deposition  from  Sulphuric  and  Nitric  Acid 

Solution. 

Filter  and  wash  as  under  (2).  Transfer  the  asbestos  film  from  the 
crucible  to  the  beaker  by  means  of  a  glass  rod  and  rinse  the  crucible 
with  about  30  c.c.  of  a  boiling  mixture  of  dilute  sulphuric  and  nitric 
acids,  containing  65  c.c.  of  sulphuric  acid  (sp.  gr.  1.84)  and  50  c.c.  of 
nitric  acid  (sp.  gr.  1.42)  in  1000  c.c.  Heat  and  agitate  until  solution  is 
complete;  filter  and  electrolyse  as  under  (2). 

(4)  Electrolytic  Deposition  from  Nitric  Acid  Solution. 

Filter  and  wash  as  under  (2).  Transfer  the  asbestos  film  and 
adhering  oxide  to  the  beaker.  Dissolve  the  oxide  still  remaining  in  the 
crucible  by  means  of  2  c.c.  of  nitric  acid  (sp.  gr.  1.42),  adding  it  with  a 
pipette  and  receiving  the  solution  in  the  beaker  containing  the  asbes- 
tos film.  Rinse  the  crucible  with  a  jet  of  water,  allow  the  rinsings  to 
flow  into  the  beaker.  Heat  the  contents  of  the  beaker  until  the  copper 
is  all  in  solution,  filter,  dilute  the  filtrate  to  a  volume  of  ioo"c.c.  or 
more,  and  electrolyse.  When  a  nitrate  solution  is  electrolysed,  the 
first  washing  of  the  deposit  should  be  made  with  water  acidified  with 
sulphuric  acid,  in  order  that  the  nitric  acid  may  be  all  removed  before 
the  current  is  interrupted. 

(5)  Volumetric  Permanganate  Method. 

Filter  and  wash  the  cuprous  oxide  as  described  for  method  (2). 
Transfer  the  asbestos  film  to  the  beaker,  add  about  30  c.c.  of  hot  water, 
and  heat  the  precipitate  and  asbestos  thoroughly.  Rinse  the  crucible 


GRAVIMETRIC    ESTIMATION    OF    SUGARS. 


325 


with  50  c.c.  of  a  hot  saturated  solution  of  ferric  sulphate  in  20  % 
sulphuric  acid,  receiving  the  rinsings  in  the  beaker  containing  the  pre- 
cipitate. After  the  cuprous  oxide  is  dissolved,  wash  the  solution  into 
a  large  Erlenmeyer  flask  and  immediately  titrate  with  a  standard 
solution  of  potassium  permanganate,  i  c.c.  of  the  permanganate  so- 
lution should  equal  o.oio  grm.  of  copper.  In  order  to  determine  the 
strength  oi  this  solution,  make  6  or  more  determinations  with  the 
same  sugar  solution,  titrating  one-half  of  the  precipitate  obtained,  and 
determining  the  copper  in  the  others  by  electrolysis.  The  average 
weight  of  copper  obtained  by  electrolysis,  divided  by  the  average 
number  of  cubic  centimetres  of  permanganate  solution  required  for 
the  titration  is  equal  to  the  weight  of  copper  equivalent  to  i  c.c.  of  the 
standard  permanganate  solution.  A  solution  standardised  with  iron  or 
oxalic  acid  will  give  too  low  results. 

(6)  Direct  Weighing  of  Cuprous  Oxide. 

Prepare  a  gooch  with  an  asbestos  felt.  First  thoroughly  wash  the 
asbestos  with  water  to  remove  small  particles,  then  follow  successively 
with  10  c.c.  of  alcohol  and  10  c.c.  of  ether,  and  dry  the  crucible  and 
contents  thirty  minutes  in  a  water-oven  at  the  temperature  of  boiling 
water. 

Collect  the  precipitated  cuprous  oxide  on  the  felt  as  usual,  thoroughly 
wash  with  hot  water,  then  with  10  c.c.  of  alcohol,  and  finally  with  10  c.c. 
of  ether.  Dry  the  precipitate  30  minutes  in  a  water-oven  at  the 
temperature  of  boiling  water;  cool  and  weigh.  The  weight  of  cuprous 
oxide  multiplied  by  0.8883  gives  the  weight  of  metallic  copper. 

The  weight  of  dextrose  corresponding  to  the  copper  obtained 
is  found  by  the  following  table: 

ALLIHN'S  TABLE  FOR  THE  ESTIMATION  OF  DEXTROSE. 


Milli-  1     Milli- 

Milli- 

Milli- 

Milli- 

Milli- 

'  Milli- 

Milli-    j     Milli- 

Milli- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

per 

trose 

per 

trose 

per 

trose 

per 

trose 

per 

trose 

10 

6.1 

20 

II  .0 

30 

16  .0 

40 

20.9 

So 

25-9 

ii 

6.6 

21 

ii.  5 

3i 

16.5 

41 

21.4 

5i 

26.4 

12 

7-i 

22 

12  .O 

32 

17.0 

42 

21.9 

52 

26.9 

13 

7-6 

23 

12.5 

33 

17-5 

43 

22.4 

S3 

27-4 

14 

8.1 

24 

13-0 

34 

18.0 

44 

22.9 

54 

27.9 

;i 

8.6 
9.0 

M 

13-5 
14-0 

35 
36 

18.5 
18.9 

JI 

23-4 
23-9 

II 

28.4 
28.8 

*7 

9-5 

27 

14-5 

37 

19.4 

47 

24-4 

57 

29-3 

18 

10.  0 

28 

IS-0 

38 

19-9 

48 

24-9 

58 

29  .8 

19    !         10.5    •          29             15.5 

39 

20.4 

49 

25-4 

59 

30-3 

326 


SUGARS. 


ALLIHN'S  TABLE   FOR   THE    ESTIMATION    OF    DEXTROSE.— 

CONTINUED. 


Milli- 

Milli- 

Milli- 

Milli- 

Milli- 

Milli- 

Milli- 

Milli-     '• 

Milli- 

Milli- 

grams 
of  cop- 

grams 
of  dex- 

i grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

Jrams 
cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

per 

trose 

per 

trose 

per 

trose 

per 

trose 

per 

trose 

60 

30.8 

126 

64.2 

192 

98.4  * 

258 

133-5 

324 

169.7 

61 

31-3 

127 

64.7 

193 

98.9 

259 

134.1 

325 

170.3 

62 

31.8 

128 

65.2 

194 

99-4 

260 

134.6 

326 

170.9 

63 
64 

32.3 
32.8 

129 
130 

65.7 
66.2 

III 

1  00.0 

100.5 

261 
262 

I35-I 
135.7 

327 
328 

171  -4 
172  .0 

6s 

33-3 

131 

66.7 

197 

IOI  .O 

263 

136  .2 

329 

172-5 

66 

33-8 

132 

67.2 

198 

ioi  .5 

264 

136.8 

330 

I73-I 

67 

34-3 

133 

67.7 

199 

102  .0 

265 

137-3 

33i 

173-7 

68 

34-8 

134 

68.2 

200 

102  .6 

266 

137-8 

332 

174.2 

69 

35-3 

i35 

68.8 

2OI 

103  .1 

267 

138.4 

333 

174-8 

70 

35-8 

136 

69.3 

202 

103.7 

268 

138.9 

334 

175-3 

7i 

36.3 

i37 

69.8 

203 

IO4  .  2 

269 

139-5 

335 

175-9 

72 

36.8 

138 

70.3 

204 

104.7 

270 

140.0 

336 

176.5 

73 

37-3 

139 

70.8 

205 

105-3 

271 

140.6 

337 

177-0 

74 

37-8 

140 

7i  -3 

206 

105-8 

272 

141  .1 

338 

177.6 

75 

38.3 

141 

71.8 

207 

106.3 

273 

I4I.7 

339 

178.1 

76 

38.8 

142 

72.3 

208 

106.8 

274 

142.2 

340 

178.7 

77 

39-3 

143 

72  .9 

209 

107.4 

275 

142.8 

341 

J79-3 

78 

39.8 

144 

73-4 

210 

107.9 

276 

143-3 

342 

179-8 

79 

40.3 

145 

73-9 

211 

108.4 

277 

143-9 

343 

180.4 

80 

40.8 

146 

74-4 

212 

109.0 

278 

144.4 

344 

180.9 

81 

41.3 

147 

74-9 

213 

109-5 

279 

145.0 

345 

i8!.s 

82 

41.8 

148 

75-5 

I        214 

IIO.O 

280 

145-5 

346 

182.1 

83 

42  .3 

149 

76.0 

215 

no.  6 

281 

I46.I 

347 

182.6 

84 

42.8 

ISO 

76.5 

j      216 

in  .1 

282 

146.6 

348 

183.2 

85 

43-4 

151 

77-0 

217 

in  .6 

283 

147-2 

349 

183.7 

86 

43-9 

152 

77-5 

1      218 

112  .1 

284 

147-7 

350 

184.3 

8? 

44-4 

153 

78.! 

219 

112.7 

285 

148.3 

351 

184-9 

88 

44-9 

154 

78.6 

!        220 

113.2 

286 

148.8 

352 

185.4 

89 

45-4 

155 

79-1 

|        221 

II3-7 

287 

149-4 

353 

186.0 

90 

45-9 

!   156 

79.6  : 

222 

114.3 

288 

149.9 

354 

186.6 

9i 

46.4 

i      T57 

80.  i 

223 

114.8 

289 

150.5 

355 

187.2 

92 

46.9 

158 

80.7 

224 

"5-3 

290 

151  -o 

356 

187-7 

93 

47-4 

159 

81  .2 

i        225 

iiS-9 

291 

151  .6 

357 

188.3 

94 

47-9 

160 

81.7 

226 

116.4 

292 

152.1 

358 

188.9 

95 

48.4 

161 

82.2 

;      227 

116.9 

293 

152.7 

359 

189.4 

96 

48.9 

162 

82.7 

|      228 

117.4 

294 

153-2 

360 

190.0 

97 

49-4 

163 

83-3 

229 

118.0 

295 

153-8 

361 

190.6 

98 

49-9 

164 

83.8 

230 

118.5 

296 

154-3 

362 

191.1 

99 

50.4 

165 

84-3 

231 

119.0 

297 

154-9 

363 

191  -7 

100 

50.9 

166 

84.8 

232 

119.6 

298 

155-4 

364 

192.3 

101 

51-4 

167 

85.3 

233 

120.  I 

299 

156  .0 

365 

192.9 

102 

51.9 

168 

85.9 

234 

I2O  .  7 

300 

156.5 

366 

193  -4 

103 

52.4 

169 

86.4 

235 

121  .2 

301 

I57-I 

367 

194-0 

104 

52.9 

170 

86.9 

236 

121.  7 

302 

157.6 

368 

194.6 

105 

53-5 

171 

87-4 

237 

122.3 

303 

158.2 

369 

I95-I 

1  06 

54-0 

172 

87.9 

238 

122.8 

304 

158.7 

370 

195-7 

107 

54-5 

173 

88.5 

239 

123.4 

305 

159-3 

371 

196.3 

1  08 

55-0 

174 

89.0 

240 

123.9 

306 

159-8 

372 

196.8 

109 

55-5 

175 

89.5 

241 

124-4 

307 

160.4 

373 

197  .4 

no 

56.0 

176 

90.0 

242 

125  .0 

308 

160.9 

374 

198.0 

in 

56.5 

177 

90.5 

243 

125-5 

309 

161.5 

375 

198  .6 

112 

57-0 

178 

91.1 

244 

126.0 

310 

162  .0 

376 

199.1 

113 

57-5 

179 

91  .6 

245 

126.6 

311 

162.6 

377 

199.7 

114 

S8.o 

180 

92.1 

246 

I27.I 

312 

163  .1 

378 

200.3 

"5 

58.6 

181 

92  .6 

247 

127.6 

313 

163.7 

379 

200.8 

116 

59-1 

182 

93-1 

248 

I28.I 

3i4 

164  .2 

380 

201  .  4 

117 

59.6 

183 

93-7 

249 

128.7 

3i5 

164.8 

38i 

202  .0 

118 

60.  1 

184 

94-2 

250 

129.2 

316 

165.3 

382 

202.5 

119 

60.6 

185 

94-7 

251 

129.7 

3i7 

165.9 

383 

203  .1 

120 

61.1 

186 

95-2 

252 

130.3 

3i8 

166.4 

384 

203.7 

121 

61.6 

187 

95-7 

253 

130.8 

319 

167.0   ! 

385 

204.3 

122 

62.1 

188 

96.3 

254 

I3I.4 

320 

167-5 

386 

204.8 

123 

62.6 

189 

96.8 

255 

I3I.9 

321 

168.1 

387 

205.4 

124 

63-1 

190 

97-3 

->S6 

132.4 

322 

168.6   ] 

388 

2o6  .O 

125 

63.7 

191 

97-8 

257 

133  .0 

323 

169.2    ' 

389 

206  .5 

GRAVIMETRIC    ESTIMATION    OF    SUGARS. 

ALLIHNS'  TABLE  FOR  THE  ESTIMATION  OF  DEXTROSE. 

CONTINUED. 


327 


Milli-        Milli- 

Milli- 

Milli- 

Milli-      Milli-         Milli-       Milli- 

Milli-      Milli- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

grams 
of  cop- 

grams 
of  dex- 

grams     grams 
of  cop-    of  dex-  ; 

grams  i    grams 
of  cop-  j  of  dex- 

per 

trose 

per 

trose 

per 

trose 

per     i     trose 

per     j     trose 

390 

207.1 

405 

215.8 

420         224.5 

435         233.4 

450 

242  .2 

39i 

207.7 

406 

216.4 

421 

225.1 

436          233.9 

451 

242.8 

392 

208.3 

407 

217.0   i 

422 

225.7 

437    i      234.5 

452 

243-4 

393 

208.8 

408 

217-5 

423         226.3          438         235.1 

453 

244.0 

394    |      209-4 

409 

218.  i 

424 

220.9            439           235.7 

454 

244.6 

395    '      210.0 

410 

218.7 

225 

227.5            440          236.3 

455 

245  -2 

396    j      210.6 

411 

219.3 

426 

228.0 

441    i      236.9 

456 

245-7 

397 

211  .2 

412 

219.9 

427 

228.6 

442          237.5 

457 

246.3 

398 

211.  7 

413 

220.4 

428 

229  .2 

443           238.1 

458    i      246.9 

399 

212.3 

414 

221.0 

429 

229.8 

444           238.7 

459    i      247.5 

400          212.9 

415 

221.6 

430 

230.4 

445           239.3 

460          248.1 

401           213.5 

416 

222  .2 

431 

231  .0           446          239  .8 

461     !      248.7 

402           214.1 

417 

222  .8 

432 

231.6           447    i      240.4 

462    i      249.3 

403 

214.6 

418 

223-3 

433           232.2             448           241  .0 

463    i      249.9 

404           215.2 

419 

223.9 

434           232.8            449           241.6    ; 

An  alternative  method  which  is  often  employed  is  as  follows: 
10  or  20  c.c.  of  each  Fehling  solution  are  placed  in  a  beaker  and  di- 
luted with  50  c.c.  of  boiling,  well  boiled,  water.  The  beaker  is  then 
immersed  in  boiling  water  bath  for  6  minutes,  at  the  end  of  which  time 
(the  liquid  being  still  perfectly  clear)  a  known  volume  of  the  solution  of 
the  reducing  sugar  is  added  and  the  beaker  kept  in  the  boiling  water 
for  a  further  12  minutes.  •  It  is  advisable  to  dilute  the  sugar  solution  to 
contain  about  0.5%  reducing  sugar.  The  solution  should  show 
blue  at  the  end  of  the  heating;  if  not,  the  assay  should  be  re- 
peated, using  less  saccharine  liquid.  After  12  minutes'  heating  the 
precipitated  cuprous  oxide  is  rapidly  filtered,  washed  with  boiling,  well 
boiled,  water,  dried  and  ignited  in  porcelain.  It  is  convenient  to  use 
a  porcelain  gooch  crucible  and  asbestos  wool  for  filtering.  The  red 
precipitate  may  be  ignited  to  black  cupric  oxide  in  this.  It  is  cooled 
under  a  desiccator  and  weighed  as  rapidly  as  possible  as  it  is  extremely 
hygroscopic. 

The  red  precipitate  may  also  be  washed  with  water,  alcohol  and 
ether  and  weighed  direct  or  it  may  be  filtered  in  a  hard  glass  tube 
and  reduced  in  hydrogen  or  it  may  be  redissolved  and  determined  by 
electrolysis.  (See  methods  i  to  6  above.) 

The  following  factors  may  be  employed  for  calculating  the  weight 
of  copper  or  copper  oxide  obtained  to  the  corresponding  quantities  of 
the  principal  kinds  of  sugar: 


328 


SUGARS. 


[    Cane  sugar 

Glucose         Ci2H22On       Milk  sugar         Maltose 
C6HI2O6  (after        ,    CI2H22On       CI2H22OIX 

inversion) 


Conner 

^634. 

r-jQ* 

77O7 

0080 

Cuprous  ox'de 

CO4.2 

4.7QO 

684.^ 

8l32 

Cupric  oxide   .        

4.C2  r 

4?  08 

61^ 

7^14 

Thus,  if  a  solution  of  o.i  grm.  of  a  sample  of  sucrose  has  been  in- 
verted and  precipitated  as  above  described,  and  the  resultant  cupric 
oxide  weighs  0.198  grm.,  then  the  total  quantity  of  sugar  (expressed  as 
sucrose)  is — 

o.  198  X- 4308  =.085298  =85. 3%. 

For  the  determination  of  small  quantities  of  reducing  sugar  in 
materials  containing  a  high  percentage  of  sucrose  slightly  modified 
methods  are  advisable.  Those  adopted  by  the  A.  O.  A.  C.  are  as 
follows : 

(a)  Estimation  in  materials  containing  i%  or  less  of  invert  sugar 
and  99%  or  more  of  sucrose  : 

Prepare  the  solution  of  the  material  to  be  examined  so  as  to  contain 
20  grm.  in  100  c.c.  free  from  suspended  impurities  by  filtration  and 
from  soluble  impurities  by  basic  lead  acetate,  removing  the  excess  of 
lead  of  means  by  sodium  carbonate.  Place  50  c.c.  of  the  mixed  copper 
reagent  and  50  c.c.  of  the  sugar  solution  in  a  beaker  of  250  c.c.  capacity. 
Heat  this  mixture  at  such  a  rate  that  approximately  four  minutes  are 
required  to  bring  it  to  boiling,  and  boil  for  exactly  2  minutes.  Add 
100  c.c.  of  cold,  recently  boiled,  distilled  water.  Filter  immediately 
through  asbestos  and  estimate  the  copper  by  one  of  the  methods 
given  on  pages  323  to  325. 

Obtain  the  corresponding  percentage  of  invert  sugar  by  the  use  of  the 
following  table: 


GRAVIMETRIC    ESTIMATION    OF    SUGARS. 


329 


Hertzfeld's  table  for  the  estimation  of  invert  sugar  in  materials  containing  i% 
or  less  of  invert  sugar  and  99  %  or  more  of  sucrose. 


Copper  reduced 
by    10  grms.   of 
material 

Invert  sugar 

Copper  re- 
duced by  10 
grms.  of 
material 

Invert  sugar 

Copper  re- 
duced   by    10 
grms.    of  ma- 
terial 

Invert  sugar 

Milligrams 

Per  cent. 

Milligrams 

Per  cent. 

Milligrams 

Per  cent. 

So 

o  .05 

120 

o  .  40 

190 

•  79 

11 

0.07 
0.09 

125 
130 

0.43 
0.45 

195 

200 

.82 
.85 

65 

O.II 

135 

0.48 

205 

.88 

70 

0.14 

140 

0.51 

210 

•  90 

11 

0.16 
0.19 

145 
ISO 

0-53 
0.56 

215 

220 

•93 
.96 

85 

0.21 

155 

0.59 

225 

•  99 

90 

0.24 

160 

0.62 

230 

.02 

95 

0.27 

165 

0.65 

235 

•05 

100 

0.30 

170 

0.68 

240 

.07 

105 

0.32 

175 

0.71 

245 

.  IO 

no 

0.35 

180 

0.74 

US 

0.38 

185 

0.76 

(b)  Method  for  Materials  Containing  More  than  i  per  cent, 
of  Invert  Sugar. — Prepare  a  solution  of  the  material  to  be  examined 
in  such  a  manner  that  it  contains  20  grm.  in  100  c.c.  after  clarification 
and  the  removal  of  the  excess  of  lead.  Prepare  a  series  of  solutions  in 
large  test-tubes  by  adding  i,  2,  3,  4,  5,  etc.,  c.c.  of  this  solution  to  each 
successively.  Add  5  c.c.  of  the  mixed  copper  reagent  to  each,  heat  to 
boiling,  boil  two  minutes,  and  filter.  Note  the  volume  of  sugar  solu- 
tion which  gives  the  filtrate  lightest  in  tint,  but  still  distinctly  blue. 
Place  20  times  this  volume  of  the  sugar  solution  in  a  100  c.c.  flask, 
dilute  to  the  mark,  and  mix  well.  Use  50  c.c.  of  the  solution  for  the 
determination,  which  is  conducted  as  described  under  (a) .  For  the  cal- 
culation of  the  result  use  the  following  formulas  and  table  of  factors  of 
Meissl  and  Hiller: 


Let  Cu  =  the  weight  of  copper  obtained; 
P  =  the  polarisation  of  the  sample; 
W  =  the  weight  of  the  sample  in  the  50  c.c.  of  the  solution 

used  for  determination; 

F  =  the  factor  obtained  from  the  table  for  conversion  of 
copper  to  invert  sugar; 

— =approximate  absolute  weight  of  nvert  sugar  =  Z; 

2 


33°  SUGARS. 


IOO 

ZX — -  =  approximate  per  cent,  of  invert  sugar  =  y; 

IOO  P 

R,  relative  number  for  sucrose; 


P+y 
loo  —  R  =  I,  relative  number  for  invert  sugar; 

r~^     XT* 

=  per  cent,  of  invert  sugar. 


W 


Z  facilitates  reading  the  vertical  columns;  and  the  ratio  of  R  to  I, 
the  horizontal  columns  of  the  table,  for  the  purpose  of  finding  the  factor 
(F)  for  calculation  of  copper  to  invert  sugar. 

Example. — The  polarisation  of  a  sugar  is  86.4,  and  3.256  grm. 
of  it  (W)  are  equivalent  to  0.290  grm.  of  copper.  Then: 

Cu_.29o_ 

2  2 

IOO  IOO 

Zx  _  te  0.145  x—^4.45-Y 

loo  P  8640 

-=95.i=R 


loo  —  R  =  ioo  —  95-i  =1  =  4-9 
R  :I=95.i  14.9 


By  consulting  the  table  it  will  be  seen  that  the  vertical  column  headed 
150  is  nearest  to  Z,  145,  and  the  horizontal  column  headed  95:5  is 
nearest  to  the  ratio  of  R  to  I,  95.1:4.9.  Where  these  columns  meet 
we  find  the  factor  51.2,  which  enters  into  the  final  calculation: 


Cu  F 


0.290  x  ci  .2 

•£-       =4-56  per  cent,  of  invert  sugar. 


„„  • 


PAVY'S  SOLUTION. 

Meissl  and  Killer's  factors  for  estimations  in  materials  in  which,  of  the 

total  sugars  present,  i  %  or  more  is  invert  sugar,  and 

99%  or  less  is  sucrose. 


33 1 


Approximate  absolute  weight  of  invert  sugar.  =  Z 

Ratio  of  sucrose   to 
invert  sugar-R:I. 

200  milli- 

175  milli- 

isomilli- 

125  milli- 

100  mill 

L-     75  milli- 

50  milli- 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent.  Per  cent.  Per  cent. 

Per  cent. 

0:100 

56.4 

55-4 

54-5 

53-8 

53- 

53-0 

53-0 

10:90 

56.3 

55-3 

54-4 

53-8            S3- 

52.9 

52.9 

20:80 

56.2 

55-2 

54-3 

53-7 

53- 

52.7 

52.7 

30:70 

56.1 

55-1    i 

54-2 

53-7 

S3- 

52.6 

52.6 

40:60 

55-9 

55-0 

54-1 

53.6 

53- 

52  .5 

52.4 

50:50 

55-7 

54-9 

54-0 

53-5 

53- 

52.3 

52.2 

60:40 

55-6 

54-7 

53-8 

53-2 

52. 

52.1 

51-9 

70:30 

55-5 

54-5 

53-5 

52.9 

52. 

Si-9 

Si.6 

80:20 

55-4 

54-3 

53-3 

52.7 

52. 

51-7 

51-3 

90:10 

54.6 

53-6 

53-1 

52.6 

52. 

Si.6 

51.2 

91:9 

54-1 

53-6 

52.6 

52  .1 

Si.6 

51.2 

50.7 

92:8 

53-6 

53-1 

52.1 

51.6 

51-2 

50.7 

50.3 

93:7 

53-6 

53-1 

52.1 

51-2 

50.7 

50.3 

49.8 

94:6 

53-1 

52.6 

Si.6 

50.7 

50.3 

49-8 

48.9 

95:5 

52.6 

52.1 

51-2 

50.3 

49-4 

48.9 

48.5 

96:4 

52.1 

51  -2 

50.7 

49-8 

48.9 

47-7 

46.9 

97:3 

50.7 

50.3 

49-8 

48.9 

47-7 

46.2 

45-1 

98:2 

49-9 

48.9 

48.5 

47-3             45-8             43-3 

40.0 

99:1 

47-7 

47-3 

46.5 

45-1     I         43-3 

41  .2 

38.1 

Titration  by  Pavy's  Ammoniacal  Cupric  Solution. — This 
modification  of  the  ordinary  mode  of  using  Fehling's  solution  for  the 
estimation  of  reducing  sugars  is  based  on  the  fact  that  in  presence  of  a 
sufficient  excess  of  ammonium  hydroxide  the  cuprous  oxide  is  not  pre- 
cipitated, but  forms  a  colourless  solution,  so  that  the  end  of  the  reaction 
is  indicated  by  the  decolonisation  of  the  blue  liquid.  As  the  ammoni- 
acal  cuprous  solution  is  extremely  oxidisable,  the  blue  colour  being 
restored  by  oxidation,  it  is  necessary  to  avoid  access  of  air.  This  is  best 
done  by  attaching  the  nose  of  the  Mohr's  burette  containing  the  sugar 
solution  to  a  tube  passing  through  the  india-rubber  stopper  of  a  flask 
containing  the  copper  solution.  A  second  tube  conveys  the  steam  and 
ammoniacal  gas  into  a  flask  of  cold  water.  It  is  desirable  to  allow  the 
end  of  the  tube  to  dip  into  a  little  mercury  placed  at  the  bottom  of  the 
water,  so  as  to  prevent  any  tendency  to  "suck  back."  A  still  better 
arrangement  is  to  pass  (by  a  third  tube)  a  slow  current  of  hydrogen  or 
illuminating  gas  through  the  flask  containing  the  boiling  copper  solution. 

To  prepare  the  ammoniacal  solution,  120  c.c.  of  the  ordinary  Feh- 
ling's solution  (see  page  318)  should  be  mixed  with  300  c.c.  of  strong 
aqueous  ammonia  (sp.  gr.  0.880),  and  with  400  c.c.  of  sodium  hydroxide 
solution  of  1.14  sp.  gr.  (=12  %).  The  mixture  is  then  made  up  to 
One  hundred  c.c.  %  of  this  solution  has  the  same  oxidising 


1000  c.c. 


332  SUGARS. 

power  on  glucose  as  10  c.c.  of  the  ordinary  Fehling's  solution,  that  is, 
it  corresponds  to  .050  grm. 

In  carrying  out  the  process,  100  c.c.  of  the  above  solution  are 
placed  in  the  flask,  a  few  fragments  of  pumice  or  tobacco-pipe  added, 
the  tubes  and  burette  adjusted,  and  the  liquid  brought  to  ebullition. 
The  sugar  solution  is  then  gradually  run  in  from  the  burette,  the 
boiling  being  continued  regularly.  The  process  is  at  an  end  when  the 
blue  colour  of  the  liquid  is  wholly  destroyed.  The  end-reaction  is  very 
sharply  marked,  but  the  reduction  occurs  more  slowly  than  with  the 
ordinary  Fehling's  solution.  The  process  is  often  a  very  useful  one, 
especially  for  the  rapid  assay  of  impure  sacchar  ne  liquids,  such  as 
beer- worts. 

O.  Hehner  has  shown  (Analyst,  1881,  6,  218)  that  the  presence  of 
alkaline  tartrates  and  carbonates,  gravely  affects  the  accuracy  of  in- 
dications obtained  by  Pavy's  solution. 

Pavy's  solution  has  been  very  largely  used  in  clinical  chemistry,  in 
particular  in  urine  analysis.  It  has,  however,  many  practical  disad- 
vantages, e.g.,  the  inconvenience  of  working  with  an  ammoniacal  so- 
lution and  the  great  dilution  as  compared  with  the  ordinary  Fehling 
solution.  It  is,  in  fact,  only  applicable  for  solution  containing  from  i 
to  10%  the  errors  involved  being  too  great  in  the  case  of  larger 
amounts.  Its  application  in  chemistry,  though  giving  very  trust- 
worthy results  in  experienced  hands,  should  be  practiced  with 
caution. 

Pavy's  solution  is  of  the  greatest  service  in  such  cases  as  studied  by 
Croft  Hill  (Trans.  Chem.Soc.,  1898,  73,  634)  and  E.  F.  Armstrong,  in 
which  it  was  required  to  ascertain  very  accurately  clinical  proportions 
of  maltose  and  glucose  in  solutions  the  total  sugar  content  of  which 
remained  constant. 

Blythe  ascertains  the  end  reaction  more  accurately  by  bubbling 
air  through  the  liquid  directly  the  decolourisation  is  complete.  The 
blue  colour  should  reappear  after  a  very  few  seconds  unless  too  much 
sugar  solution  has  been  added  when  a  longer  time  elapses. 

Pavy's  solution  possesses  a  different  oxidising  power  on  maltose 
and  lactose  from  that  exerted  by  Fehling's  test.  Its  reaction  on 
invert  sugar  is,  under  the  above-described  conditions,  only  five-sixths 
of  that  exerted  by  Fehling's  solution.  Hence  120  c.c.  of  the  latter  are 
employed  in  making  the  ammoniacal  solution,  instead  of  100,  as  would 
be  the  case  if  they  were  strictly  equivalent. 


BARFOED'S  REAGENT.  333 

Barfoed's  reagent  is  prepared  by  dissolving  13.3  grm.  of  crystal- 
lised neutral  copper  acetate  in  200  c.c.  of  i  %  acetic  acid.  (Zeit. 
Anal.  Chem.,  1873,  12,  27)  It  forms  a  delicate  test  for  dextrose  and, 
moreover,  is  not  reduced  by  either  maltose  or  lactose  under  certain 
conditions — /.  e.,  less  than  two  minutes'  heating.  More  prolonged 
heating  will  cause  hydrolysis  of  the  disaccharides  and  reduction. 
The  method  has  been  applied  quantitatively,  but  its  indications  are 
unreliable. 

The  behaviour  of  the  reagent  with  dextrose,  maltose,  lactose  and 
sucrose  has  quite  recently  been  investigated  by  Hinkel  and  Sherman 
(/.  Amer.  Chem.Soc.,  1907,  29,  1744)  who  claim  that  using  5  c.c.  of 
the  reagent  the  presence  of  0.0004  grm-  dextrose  can  be  shown,  either 
alone  or  mixed  with  di-saccharides  provided  that  the  total  weight  of 
disaccharide  does  not  exceed  0.02  grm.  The  test  is  best  performed 
by  heating  in  test-tubes  in  a  boiling  water-bath  for  3  minutes.  Under 
these  conditions  lactose  or  maltose  do  not  cause  reduction  until  heated 
for  9  or  10  minutes.  Roaf  (Bio.  Chem.  Journ.,  1908,  3,  182)  has 
made  use  of  the  method  to  demonstrate  the  hydrolysis  of  lactose  and 
maltose  by  enzymes. 

In  addition  to  the  standard  methods  just  described,  numerous 
other  copper  solutions  have  been  recommended  and  many  suggestions 
made  as  to  the  unification  of  methods. 

Preference  is  sometimes  given  to  Violette's  solution,  prepared  by 
dissolving  (i)  34.66  grm.  of  crystallised  copper  sulphate  and  making 
up  to  500  c.c.;  and  (2)  200  grm.  of  Rochelle  salt  and  130  grm.  of  so- 
dium hydroxide  and  making  up  to  500  c.c.  Equal  volumes  of  the 
2  solutions  are  mixed  as  required;  100  c.c. 'of  the  mixture  are  equal 
to  0.5  grm.  of  invert  sugar. 

H.  Pellet  (Zeit.  Ver.  deut.  Zuckerind.,  1906,  1012)  using  Vio- 
lette's solution,  modifies  the  gravimetric  process  as  follows:  40  c.c. 
of  the  copper  solution  and  10  to  20  c.c.  of  the  sugar  solution,  which 
must  not  contain  more  than  5  to  10  grm.  of  reducing  sugar  per  1000 
c.c.,  are  mixed  in  a  Jena  glass  flask,  the  volume  being  made  up  to  60 
c.c.  and  heated  in  a  boiling  water-bath  which  contains  so  much  water 
that  the  surface  of  the  outer  liquid  is  slightly  above  that  of  the  solu- 
tion in  the  flask.  The  solution  is  heated  to  from  85  to  88,°  and  kept  at 
this  temperature  for  3  minutes. 

50  c.c.  of  distilled  water  are  then  added,  the  flask  is  shaken, 
the  cuprous  oxide  allowed  to  settle  somewhat,  and  then  filtered  off 


334  SUGARS. 

through  an  ashless  filter  (9  to  n  cm.  diameter)  previously  moistened 
with  water  and  finally  washed  with  hot  water  until  the  washings  are 
neutral.  This  precipitate  and  filtrate  are  incinerated  (preferably 
in  a  muffle  heated  with  gas  or  electricity),  the  cupric  oxide  being 
weighed.  From  2  to  5  mg.  must  be  subtracted  from  the  weight  of 
cupric  oxide  to  compensate  for  the  absorption  of  salts  by  the  filter- 
paper;  the  actual  amount  must  be  directly  determined.  The  amount 
of  invert  sugar  is  determined  by  multiplying  the  weight  of  cupric 
oxide  by  0.454.  For  very  accurate  work,  however,  the  coefficient  must 
be  determined  by  a  control  analysis  with  invert  sugar.  The  above 
method  possesses  the  following  advantages  over  those  which  in- 
volve boiling  the  copper  and  sugar  solutions:  (i)  several  determina- 
tions can  be  made  simultaneously;  (2)  heating  is  very  uniform;  (3) 
reduction  is  complete;  (4)  influence  of  secondary  products,  and 
especially  of  sucrose  on  the  copper  solution,  is  diminished. 

The  method  gives  very  concordant  results,  and  clarification  with 
lead  acetate  is  unnecessary. 

Wiechmann  (Zeit.  Ver.  deut.  Zuckerind.,  1907,  65)  proposes  on 
behalf  of  the  International  Commission  the  adoption  of  the  following 
procedure  for  the  examination  of  liquid  sugar  products.  Soxhlet's 
modification  of  Fehling's  solution  is  to  be  used. 

26  grm.  of  the  syrup  are  dissolved  in  water  in  a  100  c.c.  flask, 
clarified  with  basic  lead  acetate,  excess  of  lead  being  precipitated  by 
10%  sodium  chloride  or  sulphate;  the  solution  is  made  up  to  100  c.c., 
shaken  and  filtered. 

1.  Total  Sugar. — 50  c.c.  of  this  solution  are  inverted  by  5  minutes' 
heating  at  67  to  70°  with  5  c.c.  of  hydrochloric  acid  (sp.  gr.  1.188). 
50  c.c.  of  this  are  diluted  to  loooc.c.  and  25  c.c.  of  this  last  solution, 
corresponding  to  0.1625  grm.  of  syrup,  are  neutralised  with  25  c.c.  of 
dilute  sodium  carbonate  (1.7  grm.  per  1000  c.c.).     50  c.c.  of  Fehling's 
solution  are  added,  the  mixture  heated  to  boiling  in  about  4  minutes, 
kept  boiling  for  3  minutes  and  the  cuprous  oxide  filtered  on  an  asbestos 
filter  and  weighed  as  such  and  multiplied  by  0.888  to  give  the  equivalent 
amount  of  copper. 

2.  Reducing  Sugar. — 4   c.c.   of   the   clarified  solution  are   made 
up  to  100  c.c.,  50  c.c.  of  this  are  boiled  with  50  c.c.  of  Fehling's  solution 
as  above  described.     The  difference  in  the  two  estimations  represents 
the  real  amount  of  sucrose  present.     The  original  paper  contains  very 
complete  instructions  throughout. 


SPECIAL    METHODS.  335 

An  almost  similar  procedure  is  recommended  by  Munson  and 
Walker  (/.  Atner.  Chem.Soc.,  1906,  28,  663)  who  have  drawn  up  tables 
for  use  with  the  method.  The  preparation  of  the  asbestos  for  filtering 
consists  of  a  prolonged  digestion  with  hydrochloric  acid,  followed  by 
digestion  with  sodium  hydroxide  solution,  extraction  with  boiling 
alkaline  tartrate  solution  and  digestion  with  nitric  acid. 

To  avoid  the  injurious  action  of  alkali  hydroxides,  Benedict  (/. 
Bio.  Chem.y  1907,  3,  101)  recommends  the  following  solutions: 

a.  69.3  grm.  crystallized  copper  sulphate  to  1000  c.c. 

b.  346   grm.  sodium   potassium   tartrate  and    200   c.c.    anhydrous 
sodium  cabonate  to  1000  c.c. 

c  200  grm.  of  potassium  thiocyanate.  Equal  volumes  of  these 
are  mixed  in  the  order  indicated,  more  sodium  carbonate  added, 
the  liquid  boiled  and  the  sugar  solution  run  in  till  no  further  precipi- 
tate of  cuprous  thiocyanate  is  formed  and  the  liquid  is  perfectly 
decolourised  (see  page  322). 

Bang's  method  (Biochem.  Zeits.,  1906,  2,  271)  is  based  on  the 
fact  that  cuprous  oxide  in  presence  of  potassium  thiocyanate  forms 
cuprous  thiocyanate  if  the  solution  contains  only  alkali  carbonate 
and  no  alkali  hydroxide.  The  excess  of  copper,  not  reduced  by  the 
sugar,  is  determined  by  conversion  into  cuprous  thiocyanate  by 
hydroxylamine.  Two  hundred  and  fifty  grm.  of  potassium  carbonate, 
50  grm.  of  potassium  hydrogen  carbonate  and  200  grm.  of  potassium 
thiocyanate  are  dissolved  in  about  600  c.c.  of  water  at  50-60°,  cooled 
to  30°,  and  12.5  grm.  of  copper  sulphate  dissolved  in  75  c.c.  of  water 
added.  After  standing  for  24  hours,  the  mixture  is  filtered  and  made 
up  to  1,000  c.c.  Ten  c.c.  of  the  sugar  solution  are  boiled  gently  for 
3  minutes  in  a  200  c.c.  flask  with  50  c.c.  of  the  copper  solution;  the 
whole  is  rapidly  cooled  and  titrated  till  colorless  with  a  solution 
containing  6.55  grm.  of  hydroxylamine  sulphate  and  200  grm.  of 
potassium  thiocyanate  in  2,000  c.c.  Fifty  c.c.  of  the  copper  solution 
correspond  to  about  60  grm.  of  sugar  (50  mgrm.  dextrose  =0.1376  grm. 
copper).  According  to  Jessen  Hansen  (Biochem,  Zeits.,  1908,  10, 
249),  the  method  yields  good  results,  provided  the  directions  are  fol- 
lowed in  every  detail,  particularly  as  regards  the  concentrations  and 
temperatures  at  which  the  components  of  the  standard  solutions  are 
mixed.  The  titration  with  hydroxylamine  also  necessitates  very  careful 
standardisation. 

Wagner  and  Rinch  (Chem.  Zeit.,  1906,  30,  38)  precipitate  cuprous 


336  SUGARS. 

oxide  from  Fehling's  solution  in  the  usual  manner,  dissolve  this  in 
nitric  acid  and  estimate  the  cupric  nitrate  with  the  refractometer. 

Influence  of  Special  Conditions  on  the  Reducing  Power  of 
Sugar  Solutions. — In  all  experiments  on  the  reducing  power  of 
sugar  on  metallic  solutions,  it  is  important  to  operate  as  far  as  possible 
under  constant  conditions.  Apparently  unimportant  differences,  as 
time  occupied  in  the  experiment,  amount  of  free  alkali,  presence  of 
excess  of  the  metallic  solution,  concentration  of  the  liquid,  and  other 
conditions  liable  to  differ  with  every  experiment,  are  all  factors  more 
or  less  concerned  in  the  results  obtained,  and  rigidly  accurate  results 
thus  become  impossible  in  many  cases  likely  to  occur  in  the  practical 
analysis  of  saccharine  liquid.  The  irregularities  due  to  some  of 
the  causes  have  been  studied  by  Soxhlet  (Prak.  Chem.,  [2]  21, 
227),  a  very  full  abstract  of  whose  original  paper  has  been  pub- 
lished in  English  by  C.  H.  Hutchinson  (Pharm.  Jour.,  [3]  1880-1,  n, 
721).  Soxhlet  finds  that  the  reducing  power  of  sugar  for  alkaline  cop- 
per solutions  is  only  constant  under  exactly  the  same  conditions,  and 
that  if  the  same  amount  of  sugar  act  in  one  case  on  an  amount  of  copper 
solution  which  it  is  just  able  to  reduce,  and  in  another  on  an  excessive 
quantity,  the  reducing  equivalent  will  in  the  first  case  be  found  to  be 
considerably  less  than  in  the  second.  Evidently,  therefore,  if  a  solu- 
tion of  sugar  is  added  by  small  quantities  at  a  time  to  a  copper  solu- 
tion, as  in  an  ordinary  volumetric  estimation,  the  amount  of  reduction 
effected  by  the  first  quantities  added  will  be  greater  than  that  produced 
by  the  last.  To  avoid  the  error  due  to  this  cause  Soxhlet  employs  the 
sugar  and  copper  solutions  in  the  exact  proportions  necessary  for  their 
mutual  reaction,  ascertaining  the  volumes  requisite  by  a  series  of  ap- 
proximating experiments.1 

It  will  be  seen  from  Soxhlet's  results  that  dilution  of  the  Fehling's 
solution  very  sensibly  affects  the  reducing  power  exerted  by  the 
sugar.  Thus,  one  equivalent  of  invert  sugar  in  i  %  solution  re- 
duces 10.  i  equivalents  of  cupric  oxide  when  the  undiluted  cupric  solu- 
tion is  employed,  but  9.7  equivalents  only  when  Fehling's  solution 

^hese  were  made  by  adding  to  a  carefully  measured  quantity  of  Fehling's  solution  (pre- 
pared fresh  daily),  at  the  boiling  point,  a  certain  amount  of  a  i  or  0.5%  solution 
of  the  sugar.  The  reaction  was  allowed  to  continue  for  a  specified  time,  when  the  liquid 
was  passed  through  a  plaited  filter,  and  a  portion  of  the  filtrate  acidulated  with  acetic  acid 
and  tested  with  potassium  ferrocyanide.  If  a  reddish-brown  colouration  or  precipitate 
resulted,  the  experiment  was  repeated,  a  somewhat  larger  quantity  of  sugar  solution  being 
employed,  and  so  on  until  a  measure  of  sugar  solution  was  found  that  would  exactly  suffice 
for  the  decomposition  of  the  copper  solution,  while  if  o.i  c.c.  less  of  sugar  solution  were 
employed  a  sensible  quantity  of  copper  was  found  in  the  filtrate.  Hence  the  volume  of 
sugar  solution  required  was  ascertained  to  within  o.  i  c.c. 


SPECIAL    METHODS.  337 

is  diluted  with  four  measures  of  water.  It  will  also  be  observed  that 
Soxhlet's  results  show  a  slight  but  very  sensible  difference  between  the 
reducing  power  of  dextrose  and  of  invert  sugar. 

The  consideration  of  these  differences  hardly  concerns  the  subject 
of  commercial  analysis.  The  analyst  is  recommended  to  standardise 
his  own  methods  of  manipulation  very  carefully  by  means  of  sugars 
of  known  purity  and  to  operate  as  far  as  possible  under  absolutely 
constant  conditions. 

Reaction  of  Sugars  with  Mercury  Solutions. — Several  methods 
have  been  described  of  estimating  glucoses  by  their  reducing  action 
on  mercuric  solutions,  an  alkaline  solution  of  potassium  mercuric 
cyanide  being  recommended  by  Knapp;  an  alkaline  solution  of  potas- 
sium mercuric  iodide  by  Sachsse,  and  a  solution  of  mercuric  acetate 
by  Hager.  The  first  two  of  these  reagents  have  valuable  qualities. 
They  cannot  advantageously  replace  that  of  Fehling  for  ordinary  pur- 
poses, but  may  occasionally  be  applied  with  advantage  being  unequally 
affected  by  the  different  kinds  of  reducing  sugars.  Their  use  is  also 
open  to  the  disadvantage  that  mercury  solutions  are  likewise  reduced 
by  creatin,  creatinin,  glycerol  and,  in  some  cases,  even  by  alcohol 
(Guillaume,  Gentil.  Compt.  rend.,  1881,  93!),  338). 

Knapp's  mercuric  solution  is  prepared  by  dissolving  10  grm.  of 
pure  dry  mercuric  cyanide  in  water,  adding  100  c.c.  of  sodium-hydroxide 
solution  of  1.145  sp.  gr.  and  diluting  the  liquid  to  100°  c.c.  One 
hundred  c.c.  of  this  solution  is  equivalent  to  0.202  grm.  dextrose  in 
1/2%  and  0.201  grm.  in  i%  solution,  i.  e.,  i  grm.  dextrose  in  i%  so- 
lution reduces  497.5  c.c.  Knapp's  solution. 

40  c.c.  of  the  reagent  are  diluted  to  100  c.c.,  heated  to  boiling  and 
the  sugar  solution  not  stronger  than  0.5%  is  run  in  as  quickly  as 
possible  until  the  whole  of  the  mercury  is  precipitated.  To  determine 
this  point  a  strip  of  filter-paper  is  moistened  with  the  clear  liquid  and 
treated  with  hydrochloric  acid  and  hydrogen  sulphide  for  mercury. 
This  method  and  that  of  Sachsse  has  been  carefully  investigated  by 
Otto  (/.  prak.  Chem.,  1881  [2],  26,  87). 

Sachsse's  mercuric  solution  is  prepared  by  dissolving  18  grm. 
of  pure  dry  mercuric  iodide  in  a  solution  of  25  grm.  of  potassium  iodide. 
To  this  a  solution  of  80  grm.  of  potassium  hydroxide  is  added,  and  the 
solution  diluted  to  1000  c.c.  40  c.c.  of  this  solution  are  boiled  in  a 
basin,  and  a  standard  solution  of  the  sugar  gradually  added.  The  end 
of  the  reaction  is  attained  when  a  drop  of  the  supernatant  liquid  ceases 

VOL.  1—22 


SUGARS. 

to  give  a  brown  colour  with  a  drop  of  a  very  alkaline  solution  of  stannous 
chloride.  The  end  of  the  reaction  is  well  denned,  and  the  results  are 
accurate  when  pure  dextrose  or  inverted  sugar  is  worked  with,  though 
differing  with  each.  In  presence  of  sucrose  the  results  are  quite  erro- 
neous. By  reducing  the  proportion  of  potassium  hydroxide  from 
80  grm.  to  10  grm.  per  1000  c.c.  Heinrich  finds  that  glucose  may 
be  accurately  determined  in  presence  of  very  varying  amounts  of 
sucrose. 

Soxhlet  has  shown  that  less  dextrose  is  required  the  more  slowly  it 
is  added  and  that  the  concentration  is  of  considerable  influence.  One 
hundred  c.c.  of  the  solution  require  0.325  grm.  dextrose  in  0.5  %  and 
0.330  grm.  in  i%  solution.  One  grm.  dextrose  in  r%  solution 
reduces  302.5  c.c.  Sachsse's  solution. 

For  information  respecting  other  modifications  of  these  methods 
Lippmann's  Chemie  der  Zuckerarten  should  be  consulted. 

Oerum  (Zeit.  Anal.  Chem.,  1904,  43,  356)  recommends  the  follow- 
ing method  as  rapid  and  suitable  for  clinical  work.  '  The  mercury 
reduced  from  Sachsse's  solution  is  collected  on  a  filter,  washed  with 
warm  i%  hydrochloric  acid  and  then  thoroughly  with  water, 
dissolved  in  boiling  nitric  acid  and  titrated  by  decinormal  ammonium 
thiocyanate  with  iron  alum  as  indicator  by  Volhard's  method.  The 
solution  is  standardised  by  a  known  amount  of  dextrose. 

Glassmann  (Ber.,  1906,  39,  503)  proposes  to  boil  the  dextrose 
solution  with  a  known  quantity  of  mercuric  solution  previously  stand- 
ardised gasometrically  by  hydrazine  sulphate.  The  excess  of  mercuric 
salt  remaining  unreduced  is  similarly  determined. 

Cane  Sugar. — Sucrose,  saccharose.     C12H22On. 

Cane  sugar  is  found  in  a  very  large  number  of  plants  occurring  both 
in  the  sap,  seeds  or  fruits  and  in  the  milk  of  the  coconut.  Sucrose 
is  manufactured  from  beet-root  and  the  sugar  cane  and  to  a  less  extent 
from  sorghum  and  the  sugar  maple. 

It  forms  large  transparent  colourless  crystals  having  the  form  of 
monoclinic  prisms  and  familiar  in  commerce  under  the  names  of  "sugar 
crystal"  and  "sugar  candy."  These  crystals  have  a  sp.  gr.  of  1.55 
to  i  .61  according  to  the  mode  of  crystallisation.  Cane  sugar  has 
a  rotation,  [a]D=  66.5;  [of  =  73.8. 

When  cautiously  heated  it  melts  at  about  160°  and  on  cooling  forms 


CANE    SUGAR. 


339 


a  transparent  amber-coloured  solid  known  as  barley  sugar.  Heated 
at  above  160°  it  decomposes. 

Cane  sugar  dissolves  in  about  half  its  weight  of  cold  water,  forming 
a  very  sweet  viscid  liquid  known  as  syrup.  (For  information  respecting 
the  sp.  gr.  of  sugar  solutions  see  page  289). 

In  boiling  water  it  is  soluble  in  all  proportions.  The  boiling  point 
of  an  aqueous  sugar  solution  increases  with  the  quantity  of  sugar 
dissolved  as  shown  in  the  following  table.  The  proportion  of  sugar 
present  may  thus  be  deduced  from  the  boiling  point. 


TABLE  OF  THE  ELEVATION  OF  THE  BOILING  POINT  OF  SUGAR 

SOLUTIONS. 
(Claassen-Frentzel.  Deutsche  Vereinzeitschrift,  1893,  p.  267.) 


Elevation 

Elevation 

%  sugar 

of  the 
boiling  point 

%  sugar 

of  the 
boiling  point 

F° 

F° 

75- 

13.2                               86.75 

31-1 

75-5 

87. 

76. 

14.2 

87-25 

32.5 

76-5 

14.8 

87-5 

33-2 

77- 

15-3 

87-75 

33-9 

77-5 

15-8 

88. 

34-6 

78. 

"16.4 

88.25 

35-3 

78.5 

16.9 

88.5 

36.0 

79- 

17.5 

88.75 

36.7 

18.0 

89. 

37-5 

80. 

18.6 

89.25 

38-3 

80.5 

19-3 

89-5 

81. 

19.9 

89.75 

39-9 

81  .5 

20.5 

90. 

40.7 

82. 

21  .2 

90.25 

41-5 

82.5 

22.0 

9°-5 

42.4 

83- 

22.7 

9°  -75 

43-2 

83-5 

23.6 

91. 

44.1 

84. 

24.7 

91-25 

45-i 

84-5 

25-7 

9!-5 

46.3 

85. 

26.8 

47-7 

85-5 

27.9 

92. 

50.2 

86. 

29.2 

86.25 

29.8 

86.5 

30-4 

When  subjected  to  prolonged  boiling  the  sugar  acquires  an  acid 
reaction  and  becomes  in  part  inverted. 

Cane  sugar  is  almost  insoluble    in    absolute    alcohol;    in    aqueous 


340 


SUGARS. 


alcohol  the  solubility  increases  with  the  amount  of  water.     The  fol- 
lowing table  is  due  to  Scheibler. 

SOLUBILITY  OF  SUGAR  IN  ALCOHOL  OF  DIFFERENT 
STRENGTHS. 


%   alcohol 


100  c.c.  of  the  solution        j    Sp.  gr.  of  the  saturated 


contain 


solution 


0 

85.8 

82  4. 

1.3248 

10 
ir 

79-4 
76.  < 

1.2991 

20 
2C 

73-4 
69  8 

1.236 

3° 
3^ 

66.0 
61  6 

1.2293 

40 

45 
50 

re 

56.7 
51-6 

45-7 
30  -6 

1.1823 
1.1294 

60 
65 

32-9 
25.6 

1.050 

70 

75 
80 

85 
90 

95 
97-4 

IOO 

i7.8 

II.  2 

6.4 

2.7 
0.7 

0.2 
0.08 

ooo 

0.9721 

0.8931 

0.8369 

Sucrates. — Cane  sugar  forms  definite  compounds  with  some  metal- 
lic oxides.  Thus  lime,  magnesia,  and  lead  monoxide  dissolve  with 
in  syrup,  but  are  completely  reprecipitated  by  passing  a  current 
of  carbon  dioxide  through  the  liquid.  Lead  is  attacked  by  sugar 
solutions,  slowly  in  the  cold,  but  more  quickly  at  a  boiling  heat, 
the  lead  passing  into  solution.  Several  calcium  sucrates  are  known. 
The  solution  of  calcium  sucrate  has  an  alkaline  and  bitter  taste,  and 
forms  the  liquor  colds  sacchdratus  of  pharmacy.  On  mixing  syrup 
with  a  concentrated  solution  of  barium  hydroxide,  a  crystalline  pre- 
cipitate is  obtained,  having  the  composition  C12H22BaO12  =  BaO, 
C12H22On,  or  C12H21(Ba.OH)On.  This  compound  may  be  recrystallised 
from  boiling  water,  separating  in  brilliant  scales  resembling  boric  acid. 
Its  sparing  solubility  in  cold  water  has  been  utilised  in  the  treatment 


CANE  SUGAR.  341 

of  saccharine  juices,  pure  cane  sugar  being  readily  obtainable  by  de- 
composing the  barium  sucrate  by  sulphuric  acid.  On  adding  stron- 
tium hydroxide  to  a  boiling  15%  solution  of  sugar,  the  compound 
PhH^Sr.OHJjOn  begins  to  separate,  and  when  2.5  molecules  of 
strontium  hydroxide  have  been  added  almost  the  whole  of  the  sugar 
will  be  precipitated.  The  granular  sucrate  may  be  washed  with  hot 
water,  and  decomposed  by  carbonic  acid.  This  process  is  now 
employed  in  recovering  sugar  from  molasses.1 

Crystalline  compounds  are  also  easily  obtained  with  some  sodium 
salts;  thus  there  are  sodium  chloride  compounds  Ct  H22On,  NaCl, 
2H2O  and  2C12H22OU,  3NaCl,4H2O,  which  have  a  lower  optical  rota- 
tion than  corresponds  to  the  sugar  contained  in  them.  The  sodium 
iodide  compound  2C12H2  On,  3NaI,3H2O,  which  may  be  obtained  in 
large  crystals,  has  an  optical  power  directly  proportional  to  that  of  the 
contained  sugar. 

(For  further  information  with  regard  to  the  sucrates,  the  reader  is 
referred  to  Lippman's  "  Chemie  der  Zuckerarten.") 

Detection  of  Cane  Sugar. — Cane  sugar  is  detected  more  readily 
by  its  physical  properties  than  by  its  chemical  reactions.  The  fol- 
lowing are  the  leading  characters  of  service  in  the  recognition  of  cane 
.sugar : 

The  sweet  taste  of  the  substance  or  solution. 

The  dextrorotatory  action  of  the  solution. 

The  form  of  the  crystals. 

The  characteristic  odour  produced  on  heating  the  solid  substance. 

The  production  of  saccharic  and  oxalic  acids  by  the  action  of  moder- 
ately concentrated  nitric  acid. 

The  formation  of  alcohol  by  the  prolonged  action  of  yeast  on  the 
warm  solution. 

The  increase  in  the  reducing  power  of  the  liquid  on  Fehling's  test 
after  inversion  of  the  sugar  by  treatment  with  dilute  acid,  and  the 
change  in  the  rotatory  power  of  the  solution  by  inversion. 

Tor  the  extraction  of  sucrose  from  plant-products  on  a  small  scale,  the  fine  substance 
should  be  boiled  with  strong  alcohol,  the  solution  filtered  hot,  and  allowed  to  cool,  when 
the  cane  sugar  will  usually  crystallise  out,  or  can  be  caused  to  do  so  after  concentrating 
the  solution.  If  -invert  sugar  is  also  present,  Peligot  and  Buignet  recommend  the  following 
method:  Add  to  the  juice  an  equal  measure  of  alcohol  to  prevent  fermentation  by  keeping, 
filter,  treat  the  filtrate  with  milk  of  lime  in  excess,  and  again  filter.  Boil  the  liquid  when 
calcium  sucrate  separates  in  amount  corresponding  to  two-thirds  of  the  whole  cane  sugar 
present.  The  precipitate  is  filtered  off,  washed  well,  diffused  in  water,  and  decomposed  by- 
carbonic  acid.  The  solution  is  filtered,  evaporated  at  a  gentle  heat  to  a  syrupy  consistence, 
decolourised  by  animal  charcoal,  and  mixed  with  strong  alcohol  till  it  becomes  cloudy,  when 
it  is  set  aside  to  crystallise.  If  the  solution,  after  treatment  with  carbonic  acid,  yields  a 
turbid  filtrate,  solution  of  basic  lead  acetate  is  added,  the  liquid  refiltered,  and  the  excess 
•of  lead  separated  by  hydrogen  sulphide. 


342  SUGARS. 

The  similar  change  in  the  reducing  and  rotatory  power  of  the 
solution  by  treatment  with  invertase.  This  reaction  is  very 
characteristic. 

For  information  respecting  the  distinctive  tests  for  cane  sugar,  milk 
sugar,  maltose,  and  glucoses  see  page  301. 

The  greater  number  of  the  foregoing  properties  and  reactions  of 
cane  sugar  receive  more  precise  recognition  in  the  following  section  on 
the— 

ESTIMATION    OF    CANE    SUGAR. 

Cane  sugar  may  be  estimated  by  a  variety  of  methods,  which  may 
be  conveniently  classified  according  to  the  principles  on  which  they  are 
based. 

a.  Estimation  of  Sugar  from  the  Specific  Gravity  of  the  Solu- 
tion.— For  the  employment  of  this  method  it  is,  of  course,  essential 
that  the  solvent  should  be  water,  and  that  sensible  quantities  of  foreign 
should  be  absent;  if  volatile,  like  alcohol,  they  may  be  removed  by  dis- 
tillation.    The  method  is  constantly  applied  in  sugar-works,  not  so 
much  for  ascertaining  the  amount  of  sugar  in  the  juice  as  to  obtain  an 
estimate  of  the  foreign  matters  associated  with  it;  the  sugar  present 
matters  being  really  ascertained  by  other  methods,  and  a  corresponding 
deduction  made  from  the  percentage  of  " apparent  sugar"  present. 
On  page  289  et  seq.  full  directions  are  given  for  deducing  the  propor- 
tions of  cane  sugar  contained  in  aqueous  saccharine  solutions  of  various 
densities. 

The  percentage  of  sugar  by  weight  having  been  ascertained,  the 
number  of  pounds  of  sugar  per  imperial  gallon  of  the  syrup  may  be 
found  by  multiplying  the  sp.  gr.  by  i/io  of  the  percentage  by  weight, 
and  dividing  the  product  by  1000. 

b.  Estimation  of    Cane   Sugar   by  Weighing  as  Such.— This 
method  is  employed  in  Payen's  and  Scheibler's  methods  of  sugar-assay- 
ing, and  in  a  few  other  cases. 

c.  The   estimation  of  cane  sugar  by  fermentation  is  fully  de- 
scribed on  page  298  et  seq. 

d.  The    estimation    of    sucrose  by  its  reducing    action  after 
previous  inversion  is  usually  effected  by  heating  it  with  hydrochloric 
acid  (page  313),  neutralising  with  sodium  carbonate  and  estimating 
the  resultant  invert  sugar  by  one  of  the  processes  described  in  the 


CANE    SUGAR.  343 

section  on  the  "Reducing  Action  of  Sugars."     For  every  100  parts  of 
invert  sugar  thus  found,  95  parts  of  sucrose  must  be  reckoned. 

e.  The  estimation  of  cane  sugar  by  observation  of  the  rotatory 
action  of  its  solution  has  already  been  fully  described. 

For  the  estimation  of  sucrose  in  presence  of  other  kinds  of  sugar, 
methods  a,  c,  d,  and  e  are  incapable  of  direct  application.  If  em- 
ployed both  before  and  after  inversion,  methods  d  and  e  afford  very 
satisfactory  means,  provided  that  no  other  body  is  present  which  is  apt 
to  suffer  alteration  in  its  reducing  power  or  optical  activity  by  heating 
with  dilute  acid.  This  is  not  always  the  case,  but  under  such  con- 
ditions the  substitution  of  invertase  for  dilute  acid,  as  suggested  by 
Kjeldahl,  renders  it  possible  to  effect  the  solution  of  this  somewhat 
difficult  problem  (see  page  315). 

Estimation  of  Water  in  Commercial  Sugar  Products.— Water 
is  estimated  in  granular  cane  sugars  by  exposing  5  grm.  of  the 
sample  in  a  thin  layer  to  a  temperature  of  60°,  weighing  every  hour 
until  there  is  no  further  loss.  Twelve  hours  are  frequently  required 
for  complete  desiccation.  Beet  sugars  and  good  cane  sugars  may  be 
dried  at  100°,  two  hours  being  sufficient.  Sugars  containing  much 
glucose  generally  give  too  high  a  result  if  dried  at  100°,  owing  to  a 
partial  conversion  of  the  glucose  into  glucosan  and  caramel.  Large- 
grained  refined  sugars  absorb  moisture  with  great  facility  after  drying, 
and  should  be  weighed  between  closed  watch-glasses. 

Some  operators  prefer  to  employ  a  temperature  of  1 10°  for  estimating 
the  water  in  sugar,  by  which  means  the  time  required  is  usually  greatly 
shortened. 

The  estimation  of  water  in  treacle,  beet,  cane  juice,  and  similar  articles 
is  tedious,  owing  to  the  low  temperature  which  must  be  employed,  and 
to  the  formation  of  a  skin  on  the  surface  of  the  liquid.  To  avoid  this  5 
grm.  (or  other  known  weight)  of  the  sample  should  be  dissolved  in  water, 
and  the  solution  made  up  to  100  c.c.  10  c.c.  of  this  solution  (=0.5 
grm.  of  the  original  sample)  are  poured  over  about  12  or  15  grm. 
of  previously  ignited  silver-sand,  contained  in  a  flat  dish.  The  whole 
is  dried  at  a  temperature  not  exceeding  60°  until  constant,  the  increase 
in  weight  being  due  to  the  dry  sugar  in  0.5  grm.  of  the  sample.  By 
conducting  the  desiccation  in  a  partial  vacuum,  from  which  the  moisture 
is  removed  by  sulphuric  acid  or  chloride  of  calcium,  the  operation  may 
be  finished  in  a  few  hours. 

The  A.  O.  A.  C.  method  is  as  follows: 


344  SUGARS. 

1.  In  Sugars. — Dry  from  2  to  5  grm.  in  a  flat  dish  (nickel,  plati- 
num, or  aluminum),  at  the  temperature  of  boiling  water,  for  ten  hours; 
cool  in  a  desiccator  and  weigh ;  return  to  the  oven  and  dry  for  an  hour. 
If  on  weighing  there  be  only  a  slight  change  of  weight,  the  process  may 
be  considered  finished;  otherwise  the  drying  must  be  continued  until 
the  loss  of  water  in  one  hour  in  not  great. 

2.  In  Massecuites,  Molasses,  Honeys,  and  other  Liquid  and 
Semiliquid  Products. — Prepare  pumice  stone  in  two  grades  of  fine- 
ness.    One  of  these  should  pass  through  a  i  mm.  sieve,  while  the  other 
should  be  composed  of  particles  too  large  for  a  millimeter  sieve,  but 
sufficiently  small  to  pass  through  a  sieve  having  meshes  6  mm.  in 
diameter.     Make  the  determination  in  flat  metallic  dishes  or  in  shallow, 
flat-bottom  weighing  bottles.     Place  a  layer  of  the  fine  pumice  stone  3 
mm.  in  thickness  over  the  bottom  of  the  dish,  and  upon  this  place  a 
layer  of  the  coarse  pumice  stone  from  6  to   10  mm.  in  thickness. 
Dry  the  dish  thus  prepared  and  weigh.     Dilute  the  sample  with  a 
weighed  portion  of  water  in  such  a  manner  that  the  diluted  material 
shall  contain  from  20  to  30  %  of  dry  matter.     Weigh  into  the  dish, 
prepared  as  described  above,  such  a  quantity  of  the  diluted  sample 
as  will  yield,  approximately,  i  grm.  of  dry  matter.     Use  a  weighing 
bottle  provided  with  a  cork  through  which  a  pipette  passes  if  this 
weighing  cannot  be  made  with  extreme  rapidity.     Place  the  dish  in  a 
water-oven  and  dry  to  constant  weight  at  the  temperature  of  boiling 
water,  making  trial  weighings  at  intervals  of  2  hours.     In  case  of 
materials  containing  much  laevulose  or  other  readily  decomposable 
substances,  conduct  the  drying  in  vacuo  at  a  lower  temperature.     In 
the  case  of  very  unstable  material,  the  temperature  can  safely  be 
lowered  to  70°. 

3.  Method  for  Drying  Molasses  with  Quartz  Sand. — In  a  flat- 
bottom  dish  place  6  or  7  grm.  of  pure  quartz  sand  and  a  short  stirring 
rod.     Dry  thoroughly,  cool  in  a  desiccator,  and  weigh.     Then  add  3 
or  4  grm.  of  the  molasses,  mix  with  the  sand,  and  dry  at  the  tempera- 
ture of  boiling  water  for  from  8  to  10  hours.     Stir  at  intervals  of  an 
hour;  then  cool  in  a  desiccator  and  weigh.     Stir,  heat  again  in  the  water 
oven  for  an  hour,  cool  and  weigh.     Repeat  heating  and  weighing  until 
the  loss  of  water  in  one  hour  is  not  greater  than  3  mg. 

The  sand  used  should  be  pure  quartz.  It  should  be  digested  with 
strong  hydrochloric  acid,  washed,  dried,  and  ignited,  and  kept  in  a 
stoppered  bottle. 


CANE    SUGAR.  345 

The  amount  of  water  present  may  also  be  obtained  from  the  sp.  gr 
(see  page  289). 

Estimation  of  Ash. — The  ash  of  raw  sugar  may  contain  sand 
and  other  insoluble  matters  of  mineral  origin;  various  inorganic  salts; 
and  the  non-volatile  residues  of  the  salts  of  various  organic  acids,  among 
which  may  be  acetic,  succinic,  oxalic,  malic,  tartaric,  citric,  aconitic 
(in  cane  sugar  and  juice  only),  aspartic  (peculiar  to  beet  sugar),  melas- 
sic,  saccharic,  etc. 

The  most  complete  analysis  of  sugar-ash  hitherto  published  is  one 
by  W.  Wallace  (Chem.  News.,  1878,  37,  76).  The  ash  was  derived 
from  a  Demerara  cane  sugar,  the  juice  of  which  is  supposed  to  have 
been  treated  with  lime  only.  The  raw  sugar  yielded  1.38%  of 
ash,  an  analysis  of  which  gave  the  following  results,  K2O,  29.10;  Na^O, 
1.94;  CaO,  15.10;  MgO,  3.76;  Fe203,  0.56;  A12O3,  0.65;  SiO2,  12.38; 
p2O5J  5-595  SO3,  23.75;  CO2,  4-o6;  and  Cl,  4.15%-  Total,  101.03; 
less  O  equal  to  Cl,  0.93  =  100.10. 

The  complete  incineration  of  raw  sugar  is  very  difficult  to  effect 
satisfactorily,  the  ash  obtained  being  very  fusible,  or  light  and  easily 
blown  away;  and,  as  it  consists  largely  of  potassium  carbonate,  it  is 
very  deliquescent,  and  hence  difficult  to  weigh  accurately.  To  avoid 
these  inconveniences,  it  is  usual  to  treat  the  sugar  with  sulphuric  acid 
before  igniting  it,  by  which  means  the  ash  obtained  contains  the  bases 
as  the  comparatively  little  volatile,  difficultly  fusible,  and  non-deliques- 
cent sulphates.  An  allowance  is  made  for  the  increased  weight  of  the 
ash  due  to  the  "sulphation"  by  deducting  i/io  of  its  weight. 

The  method  of  procedure  is  as  follows:  If  not  already  wet  or 
viscous,  moisten  from  2  to  4  grm.  of  the  sample  all  over  with  the 
least  possible  quantity  of  water,  and  then  with  a  little  pure  and  concen- 
trated sulphuric  acid.  Heat  the  whole  gently  till  the  frothing  ceases 
and  the  mass  forms  a  dry  cinder.  Ignite  the  charred  mass  in  a  muffle 
at  a  very  low  red  heat,  and  moisten  the  residue  again  with  sulphuric 
acid  when  the  ignition  approaches  completion.  Continue  the  ignition 
at  a  low  temperature  till  the  carbon  is  wholly  consumed,  then  heat  to 
bright  redness  for  10  minutes,  and  weigh  when  cold.  If  sand  or  clay 
be  present  in  sensible  quantity,  it  must  be  estimated  by  dissolving  the 
ash  in  hydrochloric  acid  and  weighing  the  insoluble  residue.  This  must 
be  deducted  from  the  total  ash  before  making  the  correction  of  i/io. 

By  this  method,  due  to  Scheibler,  the  bases  being  obtained  as  sul- 
phates, approximate  more  nearly  in  weight  to  that  of  the  organic  salts 


346  SUGARS. 

naturally  present  in  the  sugar  which  in  the  direct  method  are  obtained 
as  carbonates.  It  has  also  been  proposed  to  obtain  the  lead  salts  of 
the  organic  acids  by  precipitation  with  lead  acetate,  decompose  these 
and  titrate  the  acids  set  free  with  potassium  hydroxide.  The  potas- 
sium combination  approximates  closely  to  the  actual  salts  of  the  sugar. 
The  A.  O.  A.  C.  give  the  following  selection  of  methods: 

1.  Heat  from  5  to  10  grm.  of  the  material  (sugar,  molasses,  honey) 
in  a  platinum  dish  of  from  50  to  100  c.c.  capacity  at  100°  until  the  water 
is  expelled,  and  then  slowly  over  a  flame  until  intumescence  ceases. 
The  dish  is  then  placed  in  a  muffle  and  heated  at  low  redness  until 
a  white  ash  is  obtained.     If  the  substance  contains  metal  capable  of 
uniting  with  platinum,  a  dish  made  of  some  other  material  must  be 
used. 

For  soluble  ash,  digest  the  ash,  obtained  as  above  with  water,  filter 
through  a  gooch,  wash  with  hot  water  and  dry  the  residue  at  100°. 

2.  Use  50  mg.  of  zinc  oxide  to  25  grm.  of  molasses  or  50  grm.  of 
sugar.     Incorporate  thoroughly  by  adding  dilute  alcohol  and  mixing; 
dry  and  ignite  as  above.     Deduct  the  weight  of  zinc  oxide  used  from 
the  weight  of  ash. 

3.  Carbonise  the  mass  at  a  low  heat,  dissolve  the  soluble  salts  with 
hot  water,  burn  the  residual  mass  as  above,  add  the  solution  of  soluble 
salts,  and  evaporate  to  dryness  at  100°;  ignite  gently,  cool  in  a  desiccator 
and  weigh. 

4.  Saturate  the  sample  with  sulphuric  acid,  dry,  ignite  gently,  then 
burn  in  a  muffle  at  low  redness.     Deduct  i/ 10  of  the  weight  of  the  ash, 
then  calculate  the  per  cent. 

5.  Thoroughly  mix  5  grm.  of  the  material  with  a  somewhat  larger 
weight  of  pure  quartz  sand  in  a  platinum  dish ;  ignite  in  a  muffle  at  a 
moderate  red  heat. 

6.  To  avoid  the  correction  of  i/io,  as  proposed  by  Scheibler,  and 
1/5,  as  proposed  by  Girard  and  Violette,  when  sugars  are  burned  with 
sulphuric  acid,  Boyer  suggests  incineration  with  benzoic  acid  as  giving 
the  real  quantity  of  mineral  matter  without  correction. 

The  benzoic  acid  is  dissolved  in  alcohol  of  90%,  25  grm.  of 
the  acid  to  100  c.c.  of  alcohol.  5  grm.  of  the  sugar  are  weighed  in  a 
capsule  and  moistened  with  i  c.c.  of  water.  The  capsule  is  heated 
slowly  in  order  to  caramelise  the  sugar  without  carbonizing  it;  2  c.c.  of 
the  benzoic-acid  solution  are  next  added,  and  the  capsule  warmed  until 
all  the  alcohol  is  evaporated;  the  temperature  is  then  raised  until  the 


CANE    SUGAR.  347 

sugar  is  converted  into  carbon.  The  decomposing  benzoic  acid 
produces  abundant  vapours,  which  render  the  mass  extremely  porous, 
especially  if  a  circular  motion  be  imparted  to  the  capsule.  The  slow 
heating  is  continued  until  all  the  benzoic  acid  is  volatilised.  The 
carbon  obtained  is  voluminous  and  of  a  brilliant  black  colour.  The 
incineration  is  accomplished  in  a  muffle  at  a  low  red  heat.  The  cap- 
sule should  be  weighed  quickly  when  taken  from  the  desiccator,  in  order 
to  avoid  the  absorption  of  water  by  the  alkaline  carbonates.  Ammo- 
nium benzoate  may  be  employed  instead  of  benzoic  acid,  and  the  analyst 
should  previously  ascertain  that  neither  the  acid  nor  the  ammonium 
salt  leaves  a  residue  on  incineration.  In  addition  to  giving  the  mineral 
matter  directly,  this  method  permits  the  determination  of  its  composition 
also — a  matter  of  no  small  importance. 

Soluble  and  Insoluble  Ash. — Ash  the  material  according  to 
method  i ;  add  water  to  the  ash  in  the  platinum  dish,  heat  nearly  to 
boiling,  filter  through  ash-free  filter-paper,  and  wash  with  hot  water 
unti  the  filtrate  and  washings  amount  to  about  60  c.c.  Return  the 
filter-paper  and  contents  to  the  platinum  dish,  carefully  ignite,  and 
weigh.  Compute  percentages  of  water-insoluble  ash  and  water-soluble 
ash. 

Alkalinity  of  Ash. — The  filtrate  is  titrated  with  N/io  hydrochloric 
acid  and  methyl  orange.  Excess  of  this  acid  is  added  to  the  insoluble 
ash  in  the  platinum  dish  which  is  heated  nearly  to  boiling,  and 
when  cool  the  excess  is  titrated  with  N/io  sodium  hydroxide  and 
methyl-orange.  The  results  are  usually  expressed  as  the  amount 
of  decinormal  acid  required  by  the  ash  of  i  grm.  of  sample. 

Mineral  Adulterants  in  Ash. — Comparatively  large  quantities 
of  saccharine  products  may  be  readily  and  quickly  reduced  to  an  ash 
for  mineral  examination  without  the  troublesome  frothing  that  ordi- 
narily ensues  in  igniting  at  once  with  a  free  flame  by  proceeding  as 
follows  : 

Mix  loo  grm.  of  molasses,  syrup,  or  honey,  or  of  the  confectionery 
solution,  evaporated  to  a  syrupy  consistency,  with  about  35  grm.  of 
concentrated  sulphuric  acid  in  a  large  porcelain  evaporating  dish. 
Then  pass  an  electric  current  through  it  while  stirring  by  placing  i 
platinum  electrode  in  the  bottom  of  the  dish  near  one  side  and  attaching 
the  other  to  the  lower  end  of  the  glass  rod  with  which  the  contents  are 
stirred.  Begin  with  a  current  of  about  i  ampere  and  gradually  increase 
to  4.  In  from  10  to  15  minutes  the  mass  is  reduced  to  a  fine  dry  char, 


348 


SUGARS. 


which  may  then  be  readily  burned  to  a  white  ash  in  the  original  dish 
over  a  free  flame  or  in  a  muffle. 

If  an  electric  current  is  unavailable,  treat  in  a  large  porcelain  dish 
100  grm.  of  the  saccharine  solution  to  be  ashed,  which  should  be 
evaporated  to  a  syrupy  consistency  if  not  already  in  such  condition, 
with  sufficient  concentrated  sulphuric  acid  to  thoroughly  carbonise  the 
mass,  after  which  ignite  in  the  usual  manner. 

Among  the  suspected  adulterants  to  be  looked  for  in  the  ash  are 
salts  of  tin,  used  in  molasses  to  bleach  or  lighten  the  colour;  mineral 
pigments,  such  as  lead  chromate  in  yellow  confectionery  and  iron 
oxide,  the  latter  being  sometimes  used  as  an  intensifier  of  or  substitute 
for  the  natural  colour  of  chocolate. 

Tin  in  Molasses  and  other  saccharine  products. — Fuse  the  ash 
from  a  weighed  portion  of  the  sample  with  sodium  hydroxide  in  a 
silver  crucible,  dissolve  in  water,  and  acidulate  with  hydrochloric  acid; 
filter  and  precipitate  the  tin  from  this  solution  with  hydrogen  sulphide; 
wash  the  precipitate  on  a  filter  and  dissolve  it  in  an  excess  of  ammonium 
sulphide.  Filter  this  solution  into  a  tared  platinum  dish  and  deposit 
the  tin  directly  in  the  dish  by  electrolysis,  using  a  current  of  0.05  ampere. 
This  current  may  be  readily  reduced  from  an  ordinary  no- volt 
direct  circuit  by  means  of  a  series  of  lamps,  or  a  rheostat  may  be 
improvised  for  this  purpose,  consisting  of  a  long,  vertical  glass  tube, 
sealed  at  the  bottom,  containing  a  column  of  dilute  acid  through  which 
the  current  passes,  the  resistance  being  changed  by  varying  the  length 
of  the  acid  column  contained  between  two  electrodes  immersed  therein, 
one  of  which  is  movable. 

The  following  figures  illustrate  the  average  composition  of  the  ash 
of  raw  cane  and  beet  sugars,  according  to  Monier : . 


Average  composition  of  ash 


Cane  sugar  Beet  sugar 


Potassium  (and  sodium)  carbonate, 

Calcium  carbonate, 

Potassium  (and  sodium)  sulphate, . , 

'Sodium  chloride, 

Silica  and  alumina, 


16.5 
49.0 
16.0! 

9.0] 

9-5 


82.2 
6.7 

ii  .1 
none 


CANE    SUGAR. 


349 


The  following  results  by  Scheibler  are  interesting,  as  showing  the  change  produced  in 
the  weight  and  composition  of  sugar-ash  by  treatment  with  sulphuric  acid: 


Beet-sugar  Ash 


Original 

Sulphated 

Potassium  oxide 

2?  .6$ 

2s  .6=; 

Sodium  oxide, 

21  .62 

21  .62 

Calcium  oxide,.    .    .         

6.53 

6.  ^ 

Silica,     
Carbon  dioxide,  
Sulphur  trioxide,  

0.72 

22.87 
17  .63 

0.72 
none 
58.38 

Chlorine 

A  48 

none 

Undetermined  matters,  and  loss 

99-5° 
.  s!o 

112.90 
less  y\y    ii.  29 

IOO.OO 

101  .61 

The  following  analyses  by  J.  W.  Macdonald  (Chem.  News,  1878,  37,  127)  show  the  com- 
position of  the  mixed  sulphated  ash  obtained  in  the  analysis  of  many  samples  of  cane  and 
beet  sugar: 


Average  sulphated  ash 


Cane  sugar 

Beet  sugar 

Potassium  oxide 

28  70 

•7  A       IQ 

Sodium  oxide 

o  87 

II     12 

Calcium  oxide 

8    &T, 

T.    60 

^Magnesium  oxide 

2    7? 

6  -u" 
O    ID 

Ferric  oxide  and  alumina 

"•/O 

6  oo 

o  28 

Silica,  

y 

8.  20 

I    78 

Sulphur  trioxide,  

43  -6^ 

48.8s 

100.06 

100.06 

With  respect  to  these  analyses,  it  may  be  remarked  that  phosphates  were  not  sought  for 
by  Mr.  Macdonald,  but  representative  samples  showed  2.90%  of  this  in  the  cane 
sugar  ash,  and  only  0.24%  in  the  ash  of  beet  sugar.  In  the  treatment  of  beet-juice 
it  is  usual  to  employ  an  excess  of  lime,  which  is  afterwards  removed  by  carbon  dioxide. 
Hence  the  phosphates  of  the  juice  would  be  precipitated  almost  entirely  at  an  early  stage 
of  the  manufacture.  The  proportion  of  phosphates  in  the  ash  of  a  sugar  might  perhaps 
furnish  an  indirect  indication  whether  the  article  was  manufactured  from  cane  or  from 
beet.  Raw  beet  sugar,  however,  is  readily  distinguished  from  that  derived  from  the  cane 
by  the  appearance,  flavor,  and  the  small  proportion  of  dextrose,  owing  to  the  destruction 
of  the  greater  part  by  the  employment  of  a  large  excess  of  lime. 


350  SUGARS. 

According  to  Landolt,  in  the  case  of  beet  sugars,  the  ratio  between 
the  potassium  carbonate  and  the  amount  of  organic  salt  is  approximately 
as  i :  2  which  becomes  1 11.54  if  the  potassium  is  estimated  as  sulphate. 

Laugier  (Compt.  rend.,  1878,  87,  1088)  claims  to  reconstruct  the 
original  salts  in  the  following  manner.  To  a  sample,  dilute  sul- 
phuric acid  is  cautiously  added  to  set  free  the  organic  acids  which  are 
then  extracted  with  ether.  Half  this  ethereal  solution  is  added  to  the 
ash  derived  from  another  sample  of  the  sugar  of  half  the  weight, 
evaporated  down  upon  it  and  weighed. 

As  any  clay  or  sand  contained  in  a  sample  of  sugar  has  no  prejudicial 
effect  on  the  refining  process,  it  is  sometimes  desirable  to  eliminate  such 
extraneous  matters  before  determining  the  ash  proper.  This  is 
done  by  dissolving  a  known  weight  of  the  sample  in  water,  making 
the  solution  up  to  a  known  volume,  filtering  through  a  dry  filter,  evapo- 
rating one-half  of  the  filtrate  to  dryness,  moistening  the  residue  with 
sulphuric  acid,  and  igniting  in  the  usual  way. 

Extractive  Matters.  Organic  Matters  not  Sugar. — In  ordinary 
commercial  analyses  of  sugars,  the  sum  of  the  sucrose,  dextrose,  ash, 
and  water  is  subtracted  from  100.00,  and  the  difference  called  "organic 
or  undetermined  matters."  Under  the  last  denomination  are  included 
many  substances,  of  which  the  chief  are :  organic  salts  of  the  bases 
found  in  the  ash;  organic  bases,  such  as  asparagine  and  betaine; 
gummy  and  pectous  bodies;  proteins  and  enzymes;  and  insoluble 
organic  matters,  such  as  particles  of  cane.  Some  of  these  impurities 
have  no  interest  for  the  sugar  refiner,  but  others  are  very  injurious. 
Thus  the  gummy  matters  interfere  with  the  process  of  crystallisation, 
and  the  proteins  tend  to  induce  fermentation. 

Although  for  most  commercial  purposes  the  estimation  of  these  sub- 
stances by  difference  is  sufficient,  the  method  is  open  to  the  objection 
that  all  the  errors  of  the  analysis  are  thrown  on  the  organic  matters, 
and  that  such  a  method  makes  no  distinction  between  the  harmless 
and  injurious  bodies  comprised  among  the  ''organic  matters  not 
sugar."  Hence  even  rough  methods  of  obtaining  a  further  knowl- 
edge of  the  nature  and  amount  of  these  substances. have  an  occasional 
value. 

Walkoff  obtains  a  comparative  estimate  of  the  organic  matters  in 
beet  products  by  precipitating  the  solution  of  5  grm.  of  the  sugar  in 
200  c.c.  of  warm  water  by  a  solution  of  2  grm.  of  pure  tannin  in  1000  c.c. 
The  tannin  solution  is  added  from  a  burette,  and  samples  of  the  liquid 


CANE    SUGAR.  351 

filtered  from  time  to  time,  and  the  filtrate  tested  with  ferrous  sulphate, 
which  gives  a  dark  colour  as  soon  as  the  tannin  has  been  added  in  excess. 
The  tannin  is  said  to  precipitate  1/6  of  its  weight  of  organic  matters, 
but  the  process  is  chiefly  valuable  as  a  test  for  the  comparative  purity  of 
different  specimens.  Asparagine  is  not  estimated  in  this  process. 
The  sugar  solution  should  be  perfectly  neutral. 

Another  comparative  method  consists  in  precipitating  the  solution 
of  sugar  with  a  slight  excess  of  basic  lead  acetate,  and  weighing  the 
precipitate  produced,  or  the  organic  matters  recoverable  from  it  by 
decomposing  it  with  sulphuretted  hydrogen. 

Invert  sugar  in  raw  sugar  may  be  estimated  byFehling's,  Knapp's, 
or  Sachsse's  method.  Fehling's  solution  employed  gravimetrically  re- 
quires a  somewhat  longer  time  than  some  of  the  volumetric  methods. 
On  the  other  hand,  the  latter  require  that  the  solution  shall  be  tolerably 
free  from  colour. 

Dextrose,  in  a  proportion  greater  than  one-half  of  the  total  invert 
sugar,  is  not  a  normal  constituent  of  commercial  cane  sugar,  but  is 
sometimes  added  as  an  adulterant. 

Sucrose  may  be  determined  in  raw  sugar  by  the  polarimetric  method. 
In  samples  containing  but  little  invert  sugar  the  original  reading  will 
be  sufficiently  accurate  for  commercial  purposes,  but  in  other  cases 
it  should  be  supplemented  by  Clerget's  inversion-process  (page  312). 

Assay  and  Valuation  of  Raw  Sugar  Products. — Sugars,  whether 
raw  or  refined,  which  are  fit  for  direct  consumption  are  generally 
valued  for  their  appearance,  colour,  etc.,  rather  than  according  to  the 
percentage  of  sugar  present.  But  when  bought  for  the  purpose  of  re- 
fining it  is  important  to  know  not  only  how  much  sucrose  the  sample 
actually  contains,  but  also  the  available  amount  of  crystallisable  sugar. 

Two  samples  of  sugar  containing  the  same  percentage  of  sucrose 
often  differ  considerably  in  their  yield  of  crystallisable  sugar  when  re- 
fined. This  is  attributable  to  differences  in  the  nature  and  quantity 
of  the  impurities,  which  either  tend  to  destroy  the  sucrose  by  in- 
version or  prevent  its  crystallisation.  These  considerations  resulted 
in  the  adoption  of  the  assumption  that  each  unit  of  ash  prevents 
five  units  of  cane  sugar  from  crystallising,  and  that  each  unit  of  invert 
sugar  prevents  the  crystallisation  of  an  equal  weight  (or  according  to 
some  practices  twice  its  weight)  of  cane  sugar.  Hence  a  deduction 
equal  to  (twice)  the  percentage  of  invert  sugar  found  plus  5  times  the 
weight  of  the  ash,  must  be  made  from  the  content  of  cane  sugar  found 


352  SUGARS. 

by  analysis,  in  order  to  ascertain  the  percentage  of  net  obtainable  or 
.crystallisable  sugar  in  the  sample.1  This  percentage  of  crystallisable 
sugar  is  called  the  " refining  value"  of  the  sample.  The  results  of  the 
above  calculation  are  not  always  in  strict  accordance  with  the  truth, 
though  for  beet  sugar  the  variations  are  not  great  of  late  years  the 
proportion  of  organic  non-sugar  to  ash  is  said  to  have  increased. 
When  the  ratio  of  ash  to  organic  non-sugar  is  about  2:1  the  yield 
actually  obtained  is  less  than  that  calculated  by  deducting  five  times 
the  weight  of  the  ash.  Schultz  considers  that  the  out-turn  of  refined 
beet  sugar  is  equal  to  the  total  sugar  minus  twice  the  amount  of  total 
soluble  impurities. 

A  very  convenient  and  instructive  method  of  assaying  a  juice,  syrup , 
or  molasses  is  to  ascertain  the  ratio  which  exists  between  the  percentage 
of  sugar  as  determined  by  the  polarimeter  and  as  deduced  from  the 
sp.  gr.  of  the  liquid.  The  difference  between  the  two  results  is  the  per- 
centage of  " solids  not  sugar,"  and  though  the  non-identity  of  the 
solution  sp.  gr.  of  these  matters  with  that  of  sugar  prevents  the  method 
from  giving  really  accurate  results,  it  affords  a  simple  and  practical 
means  of  judging  of  the  relative  purity  of  saccharine  liquids,  and 
calculating  the  amount  of  crystallisable  sugar  obtainable  therefrom. 
The  percentage  of  " apparent  sugar,"  or  total  solids  in  the  liquid,  can 
be  deduced  from  the  table  of  sp.  gr.  on  page  289,  and  this  figure  mul- 
tiplied by  the  sp.  gr.  of  the  solution  gives  the  number  of  grm,  of  total 
sojids  per  100  c.c.  This  result  may  also  be  obtained  from  the  formulae 
on  pa£e  290,  but  for  very  strong  saccharine  liquids,  such  as  molasses, 
the  use  of  the  table  is  preferable.  From  the  contents  of  the  liquid  in 
total  solids  thus  found  there  is  subtracted  the  weight  (grm.)  of 
sugar  per  100  c.c.  found  by  the  polarimeter,  when  the  difference  is 
the  "solids  not  sugar"  per  100  c.c.  The  percentage  of  real  sugar 
contained  in  100  parts  of  total  solids,  or  ''apparent  sugar,"  is  called  the 
"  apparent-purity-coefncient "  of  the  juice. 

A  rapid  approximate  valuation  may  be  obtained  by  making  a  per- 
fectly saturated  solution  of  the  sample  in  water  at  17.5°,  and  ascer- 
taining the  sp.  gr.  of  the  liquid.  In  the  case  of  pure  sucrose  this  will 

JA  commission  appointed  by  the  French  Government  recommended  the  following  plan  of 
valuing  raw  sugars,  which  was  the  officially  recognised  method  in  France,  though  it  has  not 
met  with  general  acceptance  in  other  countries,  as  its  indications  are  liable  to  be  erroneous 
in  the  case  of  cane  sugar.  From  the  percentage  of  sucrose  shown  by  the  polarimeter  is 
substracted  the  sum  of: 

a.  Four  times  the  weight  of  the  ash.  (By  "ash"  is  meant  sulphated  ash  multiplied  by 
p.8.)  b.  Twice  the  invert  sugar  when  the  latter  reaches  i  per  cent.;  or  a  weight  equal  to  the 
invert  sugar  when  the  latter  is  between  0.5  and  i  %.  When  the  invert  sugar  is  below  0.5  % 
the  correction  b  is  neglected.  1.5  %  for  waste  in  refining. 


CAXE    SUGAR. 


353 


not  exceed  1330.0;  but  the  sp.  gr.  increases  with  the  proportion  of 
foreign  substances.  The  following  table  is  given  by  E.  Anthon 
(Jahresb.,  1868,  957): 


Percentage  composition  of  solution  saturated  at  17.5° 

Specific  gravity  of  satu- 

rated solution 

Sugar 

°ther                       Water 
substances 

1330.0 

66.66 

0.00 

33-34 

i332-2 

64.85                          2.66 

32.49 

1338-4 

63.70                          5.29 

31.01 

1344.6 

62.65 

7.76 

29.68 

i350-9 

61.42                        10.13 

28.45 

I357-2 

60.28                        12.48 

27.24 

1363.6 

59.14                        14.67 

26.19 

1370.0 

58.00                        16.82 

25.18 

1376-4 

56.85                        18.87 

24.28 

1382.9 

55.70                        20.77 

23-53 

1389.4 

54.56                        22.59 

22.85 

1395-9 

53-42 

24.36 

22.22 

1402.5 

52.28 

25.98 

21.74 

1409.2 

Si-M 

27.56 

21.30 

1415-9 

50.00 

29.00 

21  .00 

In  the  case  of  cane-juice  products,  the  "  solids  not  sugar",  are  found 
in  practice  to  prevent  the  crystallisation  of  an  equal  weight  pf.  sugar, 
but  i  %  of  the  "solids  not  sugar"  from  beet-root  will  prevent  the 
crystallisation  of  1.2%  of  sugar.  Hence  a  sugar-cane  product 
having  an  apparent-purity-coefficient  of  less  than  50  cannot  be  made 
to  yield  any  crystallisable  sugar,  and  the  same  is  true  of  a  beet-root 
product  having  a  coefficient  somewhat  greater  than  this.1  By  removing 
the  salts  even  molasses  can  be  made  to  yield  considerable  crystallised 
sugar. 

Adulteratipns  of  Commercial  Sucrose.  —  Sugar  may  contain 
woody  fibre  from  the  crushed  cane,  much  gritty  sand,  fungus  spores 
and  when  in  bulk  all  kinds  of  make-weights.  The  presence  of  sand 
and  earthy  matter  is,  of  course,  indicated  by  an  excessive  proportion 
of  ash  and  the  incomplete  solubility  in  water. 

Ultramarine  is  now  frequently  added  to  refined  sugars  to  correct 


s,  if  a  beet-juice  has  a  coefficient  of  79,  the  residue  on  evaporation  will  contain 
79%  of  sugar  and  21  of  impurities.  21X1.2  =  25.2,  which  deducted  from  79  leaves  53.8 
as  the  percentage  of  the  total  solids  obtainable  in  the  form  of  crystallisable  sugar. 

VOL.  1—23 


OF    THE 

UNIVERSITY 

OF 


354  SUGARS. 

any  yellowish  tint.  It  may  be  easily  detected  by  dissolving  the  sugar 
in  cold  water  and  allowing  the  suspended  matter  to  settle. 

Fungus  spores  are  objectionable  from  the  extreme  rapidity  with 
which,  under  suitable  conditions,  they  develop  into  a  spreading  vege- 
table growth,  especially  in  presence  of  nitrogenous  matter.  Such 
sugar  is  apt  to  undergo  fermentation  and  turn  sour,  and  preserves  made 
with  it  soon  spoil. 

The  Acarus  sacchari,  or  sugar-mite,  is  a  small  animal  closely  resem- 
bling the  itch-insect,  and,  like  it,  capable  of  burrowing  under  the  skin 
and  producing  an  irritating  pustular  disease  called  the  " grocer's  itch," 
which  attacks  those  employed  in  handling  raw  sugars. 

Starch-sugar  ("  Glucose  ")  is  employed  as  an  adulterant  of  the  lower 
grades  of  refined  cane  sugar.  The  starch-sugar  used  is  commonly  a 
highly-converted  kind,  as  the  other  varieties  are  too  deliquescent  to  be 
suitable  for  the  purpose.  Anhydrous  dextrose  is  sometimes  employed, 
and  the  adulterated  sugars  generally  contain  less  moisture  than  the 
genuine  sugars  of  the  same  grades,  which  are  known  as  "coffee 
sugars,"  and  are  always  sold  moist.  The  proportion  of  starch-sugar 
employed  as  an  adulterant  is  usually  about  20%. 

If  the  sense  of  taste  be  first  deadened  by  placing  a  pinch  of  pure 
powdered  cane  sugar  on  the  tongue,  and  then,  while  the  taste  remains, 
a  portion  of  the  suspected  sample  tested  in  the  same  way,  the  bitter- 
ness of  starch-sugar  will  be  distinctly  perceived  if  the  specimen  under 
examination  be  adulterated. 

If  the  sample  suspected  to  contain  starch-sugar  is  placed  in  a  beaker 
and  stirred  for  a  few  seconds  with  rather  less  than  its  own  weight  of 
cold  water,  any  hydrated  dextrose  will  be  seen  floating  in  the  liquid  as 
white  specks  resembling  crushed  wheat.  Anhydrous  dextrose  does 
not  behave  similarly,  the  crystals  appearing  as  translucent  as  cane 
sugar. 

When  examined  by  Fehling's  solution,  genuine  coffee  sugar  will 
rarely  cause  a  reduction  greater  than  corresponds  to  5  %  of  dextrose, 
while  a  sugar  adulterated  with  the  usual  proportion  of  starch-sugar 
will  show  a  reduction  corresponding  to  about  20  %  of  dextrose.  Ow- 
ing to  the  irregular  composition  of  commercial  starch-sugar,  the 
proportion  of  it  present  in  coffee  sugar  cannot  be  deduced  with  accu- 
racy from  the  reducing  power  of  the  sample. 

The  same  difficulty  arises  when  an  attempt  is  made  to  deduce  the 
extent  of  adulteration  from  the  optical  activity  of  the  sample;  and,  as 


MOLASSES,  TREACLE  AND  GOLDEN  SYRUP.        355 

commercial  starch-sugar  undergoes  more  or  less  change  in  its  rotatory 
power  by  inversion  with  dilute  acid,  Clerget's  method  cannot  be  em- 
ployed for  the  estimation  of  the  sucrose  present.  Nevertheless,  the 
polarimeter  affords  qualitative  results  of  great  value,  and  allows  the 
fact  of  adulteration  to  be  established  beyond  the  possibility  of  doubt. 

Some  samples  of  coffee  sugar  adulterated  with  starch-sugar  exert  a 
rotation  corresponding  with  upwards  of  100%  of  cane  sugar,  owing 
to  the  high  rotatory  power  of  maltose  and  dextrin.  Such  a  result 
is  sufficient  to  establish  the  presence  of  starch-sugar.  In  cases  of 
adulteration  by  more  highly-converted  starch-sugar,  the  direct  polari- 
metric  test  will  fail  to  indicate  the  existence  of  adulteration,  but  the 
fact  will  become  manifest  on  inversion,  which  process  will  fail  to  pro- 
duce the  same  change  in  the  polarimetric  reading  that  would  ensue  if 
only  cane  sugar  and  a  small  proportion  of  invert  sugar  are  present. 

Casamajor  has  proposed  to  utilise  the  fact  that  dextrose  has  a  higher 
optical  activity  where  freshly  dissolved  than  after  some  time.  The 
standard  weight  of  sugar  is  dissolved  in  cold  water,  made  up  to  100  c.c. 
and  the  solution  examined  in  the  polarimeter  with  as  little  delay  as 
possible.  If  the  sugar  is  genuine,  the  rotation  first  observed  will  re- 
main unchanged  for  any  length  of  time,  but  if  starch-sugar  be  present 
the  rotatory  power  will  gradually  diminish.  A  sample  examined  by 
Casamajor  showed  100.4  when  first  observed.  In  15  minutes,  the 
sugar-indication  had  fallen  to  94.3;  to  91.6  in  30  minutes;  to  90.02  in 
i  hour;  1089.7  in  3  hours;  and  to  89.3  in  5  hours,  when  it  became  station- 
ary. After  inversion,  the  sugar-indication  was  72.7  (Chem.  Neivs, 
1883,  48,  252). 

Molasses,  Treacle  and  Golden  Syrup. — These  by-products  of  the 
sugar  industry  should  consist  essentially  of  sucrose  and  invert  sugar. 
They  are  often  adulterated  with  glucose  syrup.  The  production 
tion  of  molasses  is  due  to  the  long-continued  heating  of  the  saccharine 
juice,  but  the  quality  varies  with  the  nature  and  culture  of  the  sugar- 
yielding  plant,  and  with  many  other  circumstances.  "  Refiners' 
molasses,"  the  syrup  obtained  in  the  refining  of  sugar,  retains  a  con- 
siderable amount  of  sucrose,  the  proportion  being  about  35  %  in  cane- 
sugar  molasses,  and  as  much  as  50  %  in  that  from  beet-root.  This 
is  prevented  from  crystallising  by  the  impurities  present  in  the 
raw  sugar.  The  molasses  from  raw  cane  sugar  contains  a  con- 
siderable percentage  of  invert  sugar,  from  which  beet-root  molasses 
is  comparatively  free,  but  the  latter  contains  raffinose,  aspartic  acid, 


356 


SUGARS. 


and  some  other  substances.  The  proportion  of  salts  contained  in 
beet-root  molasses  is  usually  10  to  14%,  whereas  refiners'  treacle 
from  raw  cane  sugar  rarely  contains  half  that  proportion.1 

The  following  analyses  show  the  general  composition  of  molasses : 


Su- 
crose 

Invert 
Sugar 

Ash 

Wa- 
ter 

D 

ills 
&lil 

Authority 

0 

Sugar-cane  Products: 

W    Wallace 

Golden  syrup 

39  -6 

33  •  o 

2  •  5 

22.7 

2.8 

W!  Wallace! 

Treacle  

32  -5 

37  -2 

3  -5 

23  .4 

3  -5 

W.  Wallace. 

Molasses  

48.0 

18.0 

I  .4 

31  .1 

18.0 

W.  Wallace. 

Molasses,  average  
Molasses,  refiners'  

35 
37-5 

10 

5 

20 
25 

10 

J.    H.   Tucker. 
Casa  major. 

Beet-root  Products: 

Molasses  

50  .9 

i  .  i 

12.9 

19  .  o 

16.1 

Houghton  Gill. 

Molasses,  average  
Molasses,  average  

So 
55 

trace 

10 
12 

20 
20 

20 
13 

Wigner  and  Harland. 
J.    H.    Tucker. 

Molasses,  average  

49-4 

17-1 

Payen. 

Bodenbender  found  an  average  of  1.5%  of  nitrogen  in  beet-root 
molasses,  of  which  nearly  i  %  existed  as  betaine  and  proteins,  and 
nearly  the  whole  of  the  remainder  as  aspartic  and  glutamic  acids  and 
asparagine. 

Vanillin  has  been  recently  recognised  in  beet-sugar  molasses  and  may 
even  be  extracted  from  many  samples  of  raw  sugar  by  simple  agitation 
with  ether. 

The  analysis  of  molasses  and  syrups  may  be  effected  by  the 
methods  employed  for  raw  sugar,  but  certain  modifications  are  rendered 
necessary  by  the  character  of  the  substance. 

Water  may  be  estimated  as  described  on  page  343.  When  no 
great  accuracy  is  required,  an  approximation  can  be  obtained  by  taking 
the  sp.  gr.  of  the  syrup,  .but,  owing  to  the  salts  and  extractive  matters 
of  molasses  having  different  solution-densities  from  that  of  sugar,  the 
results  are  seriously  vitiated  in  many  cases.  The  water  may  also  be 
estimated  by  Wiley's  method. 

The  ash  and  organic  matter  not  sugar  may  be  ascertained  as  in 
raw  sugars  (pages  345  to  348). 

Dextrose  may  be  estimated  in  the  usual  way  by  Fehling's  solution. 
This  is  not  seriously  affected  by  the  presence  of  the  other  organic 
matters,  unless  a  very  accurate  result  is  required,  in  which  case  the 

xThe  United  States  standards  of  purity  require  that  molasses  contains  not  more  than  25% 
of  water  and  5%  of  ash;  treacle  contains  not  more  than  25%  of.  water  and  8%  of  ash. 


MOLASSES,  TREACLE  AND  GOLDEN  SYRUP.        357 

solution  must  be  clarified  by  means  of  lead,  and  the  excess  of  lead  re- 
moved as  described  on  page  311.  The  solution  of  dextrose  should  be 
dilute. 

The  estimation  of  the  sugars  and  more  especially  of  the  sucrose 
in  cane  molasses  has  been  the  subject  of  much  discussion.  Esti- 
mation of  the  sucrose  by  direct  polarisation  is  impossible  on  account  of 
the  large  amount  of  reducing  sugars  present  and  resource  is  had  to  the 
Clerget  method,  the  inversion  being  best  performed  by  invertase. 
When  acid  is  used  the  polarisation  of  the  reducing  sugars  is  said  not  to 
be  affected,  but  some  observers  claim  that  the  polarisation  of  the 
laevulose  is  not  the  same  in  neutral  as  in  acid  solutions.  In  any  case, 
the  error  is  only  very  slight  and  can  be  obviated  by  using  invertase  to 
effect  inversion. 

When  cane-sugar  molasses  is  fermented,  the  quantity  of  alcohol  pro- 
duced is  much  less  than  that  calculated  from  the  amount  of  sucrose 
and  reducing  sugars  present.  Marker  (/.  Soc.  Chem.  Ind.,  1906,  25, 
831)  has  shown  that  this  is  due  to  the  formation  of  non-fermentable 
sugars  by  the  action  of  acids  on  the  molasses  and  that  the  quantity 
produced  by  the  action  of  acids  is  very  much  greater  than  by  that  of 
invertase.  The  excess  of  reducing  bodies  produced  by  acid  is,  there- 
fore, not  derived  from  sucrose.  If  this  result  be  accepted,  an  additional 
justification  of  the  use  of  invertase  for  inversion  is  obtained. 

Alternative  to  the  use  of  the  polarimeter  is  the  determination  of  the 
reducing  sugars  with  Fehling  solution  before  and  after  inversion  with 
invertase. 

In  the  molasses  from  beet  sugar  (more  especially)  certain  optically 
active  substances  other  than  sugar  are  present.  Of  these,  malic,  meta- 
pectic,  and  alkaline  solutions  of  aspartic  acid  are  laevorotatory,  besides 
invert  sugar  and  beet  gum.  Dextran,  asparagine,  glutamic  acid,  and 
acid  solutions  of  aspartic  acid  exercise  a  right-handed  rotation.  These 
interfering  substances,  of  which  the  dextran  and  beet  gum  are  the  most 
optically  active,  tend  in  great  measure  to  neutralise  the  effect  of  each 
other.  The  optical  effect  of  asparagine  is  said  to  be  completely  neu- 
tralised by  adding  10%  of  acetic  acid  to  the  solution  filtered  from 
the  lead  precipitate. 

If  one-half  the  standard  weight  of  syrup  be  weighed  out,  treated  with 
i  c.c.  of  lead  solution,  and  the  mixture  made  up  to  50  c.c.  by  absolute 
alcohol  and  filtered,  all  the  asparagine,  aspartic  acid,  malic  acid, 
beet  gum,  and  dextran  remain  in  the  precipitate,  while  the  presence  of 


358  SUGARS. 

the  alcohol  in  the  filtrate  is  said  to  neutralise  the  rotation  due  to  the 
invert  sugar. 

Sugar  Confectionery. — Analysis  of  sweets  is  generally  a  question 
of  the  detection  of  poisonous  colouring  materials.  The  percentage  of 
sugar  present  may  be  estimated  in  the  usual  way  and  the  presence  of 
starch-sugar  ascertained  as  described  (see  page  354).  Starch-sugar 
is  very  extensively  employed  in  the  manufacture  of  confectionery. 

Essences  may  be  dissolved  out  by  petroleum  spirit  and  identified 
by  their  odour;  those  now  used  are  often  artificial. 

Treatment  of  the  colouring  matter  with  alcohol,  with  water  and 
with  bleaching  powder  quickly  characterises  it  as  organic  or  inorganic 
in  nature. 

Among  the  red  colouring  matters  of  sugar  confectionery,  red  lead 
and  vermilion  have  been  observed,  but  in  most  cases  harmless  organic 
pigments  are  employed. 

Lead  chromate  has  been  employed  as  a  yellow  colouring  agent. 
Greens  have  been  found  to  be  produced  by  a  mixture  of  lead  chromate 
and  prussian  blue,  and  copper  arsenite,  and  other  cuprous  pigments 
have  also  been  met  with.  The  blue  mineral  colouring  matters  may  be 
of  prussian  blue  or  ultramarine.  The  detection  of  the  injurious  colour- 
ing matters  in  confectionery  belongs  to  mineral  analysis,  and  requires 
no  detailed  description  here. 

Candies  and  confections  are  now  almost  invariably  coloured  with 
coal-tar  products,  prepared  especially  for  the  purpose  and  free  from 
metallic  impurities.  In  most  cases  very  small  amounts  of  colour  are 
used. 

Under  a  regulation  issued  in  accordance  with  the  provisions  of  the 
U.  S.  (Federal)  food  law  the  following  eight  colours  are  permitted  in 
candies  and  confections,  the  manufacture  and  sale  of  which  are 
within  the  jurisdiction  of  the  law.  The  numbers  refer  to  Schultz  & 
Julius'  Systematic  Survey  of  Organic  Coloring  Matters  (translated  by 
Green): 

107  Carmosine  B. 
56  Scarlet  40. 
517  Eosin  B.  C. 
85  Orange  G. 

4  Yellow  F.  Y. 
435  Acid  green  GG. 
692  Indigotin. 


SUGAR-CANE   AND    BEET    JUICES. 


359 


The  manufacturer  of  the  said  dyes  is  required  to  guarantee  that 
they  really  are  what  they  are  represented  to  be,  that  they  are  not 
mixtures  and  that  they  do  not  contain  harmful  impurities. 

Sugar-cane  and  Beet  Juices. 

The  juice  obtained  by  crushing  and  pressing  the  sugar-cane1  has  usu- 
ally a  sp.  gr.  of  1.070  to  1.090,  but  has  been  met  with  as  low  as  1.046 
and  as  high  as  i.no.  It  is  an  opaque,  frothy,  yellowish-green  liquid. 
On  nitration  it  yields  a  pale  yellow  fluid,  which  is  nearly  pure  syrup, 
the  greenish  scum  containing  chlorophyll,  a  peculiar  wax  called  cerosin, 

!The  following  analyses  show  the  general  composition  of  the  sugar-cane: 


Locality  and  kind  of 

Water 

Sug 

'ar 

Woody 

Salts 

Authority 

cane 

fibre 

Martinique  
Guadaloupe  

72.1 
72.0 

18 
17 

.0 

.8 

9-9 
9.8                      0.4 

Peligot. 
j   Dupuy. 

Havana  

77.0 

12 

.0 

II  .0 

!  Casaseca. 

Cuba  

65  .9 

I? 

.  7 

16.4 

i  Casaseca. 

Mauritius  

69  .0 

20 

.0 

IO.O 

I  .0 

leery. 

Ribbon  cane  

76  .73 

13 

•39 

9.07 

•39 

Avequin. 

Tahiti  

76.08 

14 

.28    : 

8.87 

•  35 

Avequin. 

The  following  is  a  more  detailed  analysis,  by  Payen,  of  Otaheite  cane  at  maturity: 

Water 71-04 

Sugar 18.00 

Cellulose,  ligneous  matter,  pectin,  and  pectic  acid 9 . 56 

Proteins o .  55 

Cerosin;  red,  green,  and  yellow  colouring  matters;  fatty 
matter;  resins;  essential  oil;  aromatic  matter;  and  a  de- 
liquescent substance °-37 

Insoluble  salts,  0.12;  soluble,  0.16,  consisting  of  phos- 
phates, sulphates,  chlorides,  oxalates,  acetates,  malates,  o .  28 


99.80 

According  to  Casaseca,  the  lower  portions  of  the  sugar-cane  are  the  richest  in 
sugar,  the  centre  being  of  about  the  average  composition.  This  is  shown  by  the 
following  analysis  by  Gill  of  carefully  sampled  good  average  cane  from  the  Aska 
district,  Madras: 


A 

» 

C 

Two  feet  top 

' 

Two  feet  middle 

Two  feet  root 

Megass  proper  
Juice  
Containing,  cane  sugar  
Containing,  invert  sugar.  .  .  . 

7-63% 
92.37% 
10.63% 
2.64% 

8-47% 
91-58% 
i3-3i% 
1-51% 

8-30% 
91.70% 

13-37% 
i-54% 

360 


SUGARS. 


protein  matters,  fibre,  and  a  considerable  proportion  of  mineral  matter. 
The  pure  or  nearly  colourless  juice  from  which  the  green  matter  has 
been  separated  contains  in  100  parts:  water,  81.00;  sugar,  18.20;  or- 
ganic matters  precipitated  by  lead  salts,  0.45 ;  and  mineral  matters,  0.35. 

The  sp.  gr.  of  the  juice  from  the  white  beet1  is  usually  between  1060 
and  1070,  occasionally  reaching  1078.  Beet  juice  contains  a  large 
amount  of  foreign  matters  in  proportion  to  the  sugar,  a  fact  that  renders 
the  manufacture  of 'sugar  from  beet-root  much  more  troublesome  than 
from  cane.  The  average  percentage  composition  of  expressed  beet 
juice  is  approximately: — water,  82.68;  sugar,  11.25;  other  organic  mat- 
ters, 1.47;  and  mineral  matters,  0.67. 

The  analysis  of  cane  and  beet  juices  may  be  effected  by  the  method 
described  under  " Molasses"  and  "Raw  Sugar." 

The  methods  in  vogue  for  the  estimation  of  sugar  in  the  beet, 
which  is  first  reduced  to  a  pulp  by  a  suitable  press,  are  as  follows:  (a) 
Warm  alcohol  extraction  (Sickel-Soxhlet) ;  (6)  and  (c)  hot  or  cold  alcohol 
digestion;  (d)  hot  aqueous  digestion;  (e)  cold  water  digestion  (Pellet). 

The  expressed  juice  had  the  following  composition: 


• 

A 

B 

C 

Cane  ^ugar 

ii   ^i 

14.    ee 

14.  s;8 

Invert  sugar 

2  86 

i  6; 

i  68 

Ash 

•7-2 

28 

.2=; 

Unknown.     .  .    . 

ro 

02 

.40 

Apparent  solids  ... 

IS      2O 

17   40 

17  .00 

Water  

84.     80 

82.60 

81.00 

IOO.OO 

100.00 

100.00 

The  megass  referred  to  above  contains  little  but  woody  fibre,  as  the  sugar  is 
extracted  in  the  Aska  district  by  the  diffusion  process.  Ordinary  megass  or  mill- 
trash  after  passing  the  rollers  retains  8  or  10  %  of  sugar  and  50  %  of  water. 

The  ash  of  the  sugar-cane  contains  about  50  of  silica,  5  to  8  of  phosphoric  acid, 
and  different  proportions  of  potassium.  Sodium  appears  to  be  a  constant 
constituent. 

1  The  following  is  an  analysis  by  Payen  of  the  white  or  sugar  beet: 
Water, 
Sugar, 
Cellulose, 
Proteins, 
Fatty  matter, 
Pectin  matters,  asparagine,  aspartic  acid,  betain; 

oxalates,  nitrates,  phosphates,  3  . 7 


2.7 
ii  -3 
0.8 
i  -5 
o .  i 


MALTOSE.  361 

For  the  cold  solution  processes  a  more  finely  divided  pulp  is  required. 
The  alcohol  extraction  is  perhaps  the  most  accurate,  Pellet's  process 
the  most  widely  used  in  factories. 

Alcohol  Extraction. — The  normal  weight  of  beet  pulp  with  the 
addition  of  3  cm.  of  lead  acetate  is  extracted  with  absolute  alcohol  in  a 
Soxhlet  until  the  sugar  has  all  gone  into  solution.  The  alcoholic 
solution  is  made  up  to  100  c.c.  and  polarised  in  a  200  mm.  tube  when 
the  percentages  of  sugar  is  read  off  directly. 

Alcohol  Digestion. — Twice  the  normal  weight  of  pulp  with  3  or 
4  c.c.  of  lead  acetate  is  heated  15  to  20  minutes  with  90%  alco- 
hol; the  flask  is  cooled  to  20°  and  filled  up  to  the  mark  201.2  c.c., 
the  additional  volume  of  1.2  c.c.  being  to  correct  for  the  volume  of 
the  marc  and  the  lead  precipitate.  The  solution  is  filtered  and 
polarised  as  usual.  The  cold  extraction  with  alcohol  is  performed 
in  a  similar  flask,  likewise  the  hot  aqueous  digestion. 

Pellet's  cold  aqueous  digestion  method  consists  in  taking  26.0  grm. 
of  very  finely  pulped  beet,  5  to  6  c.c.  lead  acetate,  adding  cold  water 
nearly  to  the  mark,  shaking  vigorously,  making  up  to  200.6  c.c.  and 
filtering.  The  liquid  is  polarised  and  the  sugar  value  obtained  doubled 
to  give  the  percentage  in  the  beet  pulp. 

Davoll  (J.Amer.  Chem.  Soc.,  1906,  28,  1606-1611)  proposes  as  a 
rapid  modification  of  the  above  to  take  52  grm.  of  pulp,  make  up  with 
lead  acetate  and  water  to  209.2  grm.  in  a  beaker  instead  of  in  a  flask. 

MALTOSE 

is  the  chief  product  of  degradation  of  starch  and  also  occurs  in  the 
leaves  of  some  plants.  It  usually  occurs  in  fine  crystalline  needles 
of  the  hydrate  C12H22O11,H2O.  The  amorphous  anhydride  is  very 
hygroscopic.  A  convenient  method  for  the  preparation  of  pure  mal- 
tose is  given  by  Baker  and  Day.  (Analyst,  1908,  33,  393).  Maltose 
is  hydrolysed  to  two  molecules  of  dextrose  when  heated  with  dilute 
acids,  but  is  far  more  stable  than  is  sucrose  (see  page  296).  Hy- 
drolysis takes  place  more  rapidly  under  the  influence  of  a  specific 
enzyme,  maltase.  This  enzyme  affords  an  absolute  means  of  identify- 
ing maltose;  it  is  contained  in  dried  yeast  (see  Invertase,  page  314) 
and  may  be  prepared  by  extracting  this  for  an  hour  with  20  times  its 
weight  of  water  at  about  20°  and  filtering.  A  few  c.c.  of  this  extract 
are  added  to  50  c.c.  of  a  5  %  solution  of  the  carbohydrate  under  ex- 
amination, a  little  toluene  is  added  and  the  whole  is  incubated  in  a 


362  SUGARS. 

closed  flask  at  37°  for  24  hours.  The  optical  activity  or  cupric  reduc- 
ing power  may  be  taken  before  and  after  the  action,  change  denoting 
the  presence  of  maltose.  (See  also  Barfoed's  reagent,  page  333.) 

Maltose  is  not  fermented  directly  by  yeast,  but  is  first  hydrolysed  to 
dextrose  by  the  maltase  present  in  most  yeasts,  and  this  dextrose  is 
converted  into  alcohol  and  carbon  dioxide  by  the  yeast.  Some  species 
of  yeast — 5.  marxianus,  S.  exiguus,  S.  Ludwigii,  W.  anomala,  W . 
Saturnus  (see  E.  F.  Armstrong,  Proc.  Roy.  Soc.,  1905,  76  B,  600) — 
do  not  contain  maltase  and  are  therefore  incapable  of  fermenting 
maltose.  Use  may  be  made  of  these  yeasts  to  detect  traces  of  dex- 
trose or  laevulose  present  in  maltose,  as  these  sugars  will  form  carbon 
dioxide  when  fermented,  whilst  the  maltose  remains  unattacked. 

Maltose  has  a  value  for  [a]D  =  138°  (see  page  305)  and  shows 
birotation  (see  page  315);  the  rotation  of  a  freshly  dissolved  specimen 
increases  on  keeping  or  on  the  addition  of  a  trace  of  ammonium 
hydroxide.  Maltose  resembles  the  glucoses  in  its  power  of  reducing 
hot  Fehling's  solution  without  previous  inversion,  but  the  amount  of 
cuprous  oxide  precipitated  is  only  62  %  of  that  reduced  by  an  equal 
weight  of  dextrose. 

The  reducing  power  of  maltose  is  60.8  according  to  Brown  and 
Heron,  assuming  1038.6  to  be  the  sp.  gr.  of  a  solution  of  maltose 
containing  10  grms.  per  100  c.c.  Correcting  this  for  the  true  sp.  gr. 
found  by  them  (1039.3)  the  value  of  K  becomes  61.9  (Journ.  Chem. 
Soc.,  1879,  35,  618). 

Soxhlet  states  that  the  cupric  reducing  power  (K)  is  61  when  the 
maltose  is  contained  in  a  i  %  solution,  and  the  Fehling  reagent  is  un- 
diluted and  employed  in  the  exact  proportion  necessary;  64.1  when  the 
copper  solution  is  previously  diluted  with  4  volumes  of  water;  and  65.3 
when  twice  as  much  of  this  diluted  Fehling's  solution  is  used  as  is 
required  for  the  reaction  (/.  pr.  Chem.,  1880,  [2],  21,  227). 

When  a  solution  of  maltose  is  treated  with  a  volume  of  Fehling's 
solution  sufficient  for  its  oxidation,  the  mixture  heated,  and  the  cu- 
prous oxide  filtered  off  in  the  usual  way,  a  solution  is  obtained  which, 
if  acidulated  with  hydrochloric  acid  and  heated,  acquires  the  property 
of  reducing  an  additional  quantity  of  Fehling's  solution.  This  second 
reduction  is  somewhat  more  than  half  the  first,  so  that  the  two  together 
approach  to  the  reducing  power  of  dextrose.  A  similar  behaviour  is 
exercised  by  milk  sugar  (Herzfeld,  Annalen,  1883,  220,  206). 

According  to  I.  Steiner,  the  reducing  action  of  maltose  on  Pavy's 


MALTOSE. 


363 


ammoniacal  cupric  solution  is  the  same  as  upon  the  ordinary  Fehling\s 
reaction.  Thus,  20  c.c.  of  Fehling's  solution  will  require  the  same 
volume  of  maltose  solution  for  its  reduction,  whether  used  direct 
or  previously  mixed  with  40  c.c.  of  strong  ammonia,  and  titrated  as 
described  on  page  331  (Yoshida,  Chem.  News,  1881,  43,  29).  On 
the  other  hand,  the  addition  of  more  sodium  hydroxide  in  presence 
of  ammonia  increases  the  oxidising  power  of  the  copper  solution  to 
a  notable  extent  (Chem.  News,  1880,  42,  45). 

The  estimation  of  maltose  in  cases  of  practical  interest,  viz.:  in 
starch-sugar  and  brewing  materials,  is  described  elsewhere.  The 
general  methods  already  described  are  all  applicable  to  maltose,  i 
grm.  of  maltose  in  i  %  solution  corresponds  to  317.5  c.c.  of  Knapp's 
and  197.6  c.c.  of  Sachsse's  solution. 

The  A.  O.  A.  C.  method  of  estimating  maltose  is  as  follows: 
Place  50  c.c.  of  the  mixed  copper  reagent  in  a  beaker  and  heat  to  the 
boiling  point.  While  boiling  briskly,  add  25  c.c.  of  the  maltose  solution 
containing  not  more  than  0.250  grm.  of  maltose  and  boil  for  4  minutes. 
Filter  immediately  through  asbestos  and  ascertain  the  amount  of  copper 
reduced  by  one  of  the  methods  given,  page  323.  Obtain  the  weight 
of  maltose  equivalent  to  the  weight  of  copper  found  from  the  following 
table : 

TABLE  FOR  THE  ESTIMATION  OF  MALTOSE. 

(According  to  Wein.) 


Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

3i 

34.9 

26.1 

51 

57  -4 

43-5 

7i 

79-9 

61  .0 

32 

36.0 

27.0 

52 

58.5 

44-4 

72 

81.1 

61.8 

33 

37.2 

27.9 

53 

59-7 

45  -2 

73 

82.2 

62.7 

34 

38.3 

28.7 

54 

60.8 

46.1 

74 

83-3 

63.6 

35 

39-4 

29.6 

55 

61  .9 

47-0 

75 

84-4 

64-5 

36 

40.5 

30.5 

56 

63.0 

47-8 

76 

85.6 

65-4 

37 

41-7 

31  -3 

57 

64.2 

48.7 

77 

86.7 

66.2 

38 

42.8 

32.2 

58 

65.3 

49-6 

78 

87.8 

67.1 

39 

43-9 

33-1 

59 

66.4 

50.4 

79 

88.9 

68.0 

40 

45-0 

33-9 

60 

67.6 

Si-3 

80 

90.1 

68.9 

41 

46.2 

34-8 

61 

68.7 

52  .2 

Si 

91  .2 

69.7 

42 

47-3 

35-7 

62 

69.8 

53-1 

82 

92.3 

70.6 

43 

48.4 

36.5 

63 

70.9 

53-9 

83 

93-4 

7i  -5 

44 

49-5 

37.4 

64 

72.1 

54.8 

84 

94-6 

72.4 

45 

50.7 

38.3 

65 

73-2 

55-7 

85 

95-7 

73-2 

46 

Si-  8 

39.1 

66 

74-3 

56.6 

86 

96.8 

74.1 

47 

52.9 

40.0 

67 

57-4 

87 

97-9 

75-0 

48 

54.0 

40.9 

68 

76.6 

58.3 

88 

99-1 

75-9 

49 

55-2 

41.8 

69 

77-7 

59.2 

89 

100.2 

76.8 

50 

56.3 

42.6 

70 

78.8 

60.  i 

90 

ioi  .3 

77-7 

364 


SUGARS. 


TABLE  FOR  THE  ESTIMATION  OF  MALTOSE.— CONTINUED. 


Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
'     prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

Milli- 
grams 
of  cop- 
per 

Milli- 
grams 
of  cu- 
prous 
oxide 

Milli- 
grams 
of  mal- 
tose 

9i 

102.4 

78.6 

146 

164  .4 

127.8 

201 

226  .3 

77-0 

92 

j      103.6 

79-5 

147 

165.5 

128.7 

202 

227.4 

77-9 

93 

104.7 

80.3 

148 

166.6 

129  .6 

203 

228.5 

78.7 

94 

!     105.8 

81.2 

149 

167.7 

130.5 

204 

229.7 

79.6 

95 

107.0 

82.1 

ISO 

168.9 

131  -4 

205 

230.8 

80.5 

96 

108.1 

83.0 

151 

170.0 

132.3 

206 

231.9 

j      181.4 

97 

109  .2 

83.9 

152 

171  .1 

133-2 

207 

I      233.0 

182.3 

98 

II0.3 

84.8 

153 

172.3 

I34-I 

208 

234.2 

183.2 

99 

in.  5 

85-7 

154 

173  -4 

135-0 

209 

235.3 

184.1 

IOO 

112  .6 

86.6 

155 

174-5 

135-9 

210 

236.4 

185.0 

101 

113.7 

87.5 

156 

I75-6 

136.8 

211 

237.6 

185.9 

102 

114.8 

88.4 

157 

176.8 

137-7 

212 

238.7 

!      186.8 

I03 

116  .0 

89.2 

158 

177-9 

138.6 

213 

239.8 

187-7 

104 

117  .1 

90.1 

159 

179-0 

139-5 

214 

240.9 

188.6 

105 

118.2 

91  .0 

160 

180.1 

140.4 

215 

242  .1 

189.5 

106 

119.3 

9i.9 

161 

181.3 

I4I-3 

216 

243-2 

190.4 

107 

120.5 

92.8 

162 

182.4 

142  .2 

217 

244-3 

191.2 

108 

I  2  I  .  6 

93-7 

163 

183-5 

I43-I 

218 

245-4 

192.1 

109 

122.7 

94.6 

164 

184.6 

144  -0 

219 

246  .6 

193-0 

no 

123.8 

95-5 

165 

185.8 

144-9 

220 

247-7 

193-9 

in 

125  .0 

96.4 

166 

186.9 

145-8 

221 

248.7 

194.8 

112 

I26.I 

97-3 

167 

188.0 

146.7 

222 

249.9 

195-7 

113 

127.2 

98.1 

168 

189.1 

147.6 

223 

251  .0 

196  .6 

114 

128.3 

99.0 

169 

190.3 

148.5 

224 

252.4 

197-5 

us 

129.6 

99-9 

170 

191  -4 

149-4 

225 

253-3 

198.4 

116 

130.6 

100.8 

171 

192.5 

150.3 

226 

254-4 

199.3 

117 

I3I.7 

101  .7 

172 

193.6 

151  -2 

227 

255  -6 

2OO  .  2 

118 

132.8 

102  .6 

173 

194-8 

152.0 

228 

256.7 

201  .1 

119 

134  .0 

103.5 

174 

195  -9 

152.9 

229 

257-8 

202  .0 

120 

135.1 

104.4 

175 

197.0 

153.8 

230 

258.9 

202  .9 

121 

136.2 

105.3 

176 

198.1 

154.7 

231 

260.1 

203.8 

122 

137.4 

106.2 

177 

199-3 

155  -6 

232 

26l  .2 

204  .  7 

I23 

138.5 

107  .1 

178 

200.4 

156.5 

233 

262  .3 

205  .6 

124 

139.6 

108.0 

179 

201  .5 

157-4 

234 

263.4 

206.5 

125 

140.7 

108.9 

180 

2O2  .6 

158.3 

235 

264  .6 

207.4 

126 

141  .9 

109.8 

181 

203.8 

159-2 

236. 

265.7 

208.3 

127 

143.0 

110.7 

182 

204.9 

160.1 

237 

266.8 

209.1 

128 

144.1 

1  1  1  .6 

183 

206.O 

160.9 

238 

268.0 

210.0 

129 

145.2 

112.  5 

184 

207  .1 

161.8 

239 

269.1 

210.9 

130 

146.4 

113-4 

.      185 

208.3 

162  .7 

240 

270.2 

211  .8 

131 

147.5 

114-3 

186 

209.4 

163.6 

241 

271  -3 

212.7 

132 

148.6 

-115-2 

187 

210.5 

164.5 

242 

272  .5 

213  .6 

133 

149.7 

116  .  i 

188 

211  .7 

165  .4 

243 

273-6 

214-5 

134 

150.9 

117.0 

189 

212.8 

166.3 

244 

274-7 

215  .4 

135 

152  .0 

117.9 

190 

213.9 

167  .2 

245 

275-8 

216  .3 

136 

153.1 

118.8 

191 

215.0 

I68.I 

246 

277.0 

217  .2 

137 

154.2 

119.7 

192 

2l6  .2 

169  .0 

247 

278.1 

218.1 

138 

155.4 

120.6 

193 

217-3 

169.8 

248 

279.2 

219.0 

139 

156.5 

121.5 

194 

2l8.4 

170.7 

249 

280.3 

219.9 

140 

157.6 

122.4 

195 

219.5 

171  .6 

250 

281.5 

220.8 

141 

158.7 

123.3 

196 

220.7 

172.5    ! 

142 

159.9 

124.2 

197 

221  .8 

173-4 

143 

161  .0 

125  .1 

198 

222.9 

174-3   ! 

144 

162  .1 

126.0 

199 

224.0 

175-2   , 

145 

163.2 

126.9 

200 

225.2 

176.1   j 

LACTOSE.  365 

Maltose  may  be  distinguished  from  dextrose  by  its  neutral  behaviour 
towards  copper-acetate  solution  (Barfoed's  reagent)  and  by  the  solu- 
bility of  its  osazone  in  hot  water. 

On  heating  with  phenylhydrazine  at  the  temperature  of  the  water- 
bath,  dextrose  or  laevulose  gives  a  precipitate  of  the  phenylosazone 
after  10  minutes,  but  maltose  forms  a  precipitate  only  on  cooling  the 
solution  after  an  hour's  heating.  The  osazones  of  the  two  sugars  can 
thus  be  separated  easily  from  a  solution  containing  both  sugars.  Mal- 
tosazone  is  soluble  in  about  75  parts  of  hot  water,  whereas  glucosazone 
is  almost  insoluble.  When  testing  a  freshly  prepared  mixture  of  osa- 
zones in  this  manner,  it  is  essential  to  first  wash  them  thoroughly 
with  water  and  benzene  so  as  to  remove  products  which  tend  to 
make  glucosazone  appear  soluble.  Maltosazone  is  soluble  in  a  cold 
mixture  of  equal  parts  of  water  and  acetone. 

Baker  and  Dick  (Analyst,  1905,  30,  79)  state  that  small  quantities 
of  maltose  may  be  estimated  with  a  fair  degree  of  accuracy  by  taking 
the  reducing  power  before  and  after  inversion.  They  consider  that, 
depending  on  the  osazone  reaction  alone,  it  is -impossible  to  detect  less 
than  15%  of  maltose  in  admixture  with  dextrose.  Small  quanti- 
ties of  maltose  may  be  identified  after  first  removing  the  dextrose  by 
fermentation  with  S.  marxianus. 

LACTOSE. 

Milk  sugar  reduces  Fehling's  copper  solution,  the  reducing  power 
being  roughly  half  that  of  dextrose.  It  rapidly  reduces  ammoniacal 
silver  nitrate.  The  osazone  is  soluble  in  boiling  water  and  it  may 
thus  be  detected  in  presence  of  the  glucoses  or  galactose.  Character- 
istic of  lactose  and  galactose  is  the  formation  of  mucic  acid  when  oxi- 
dised by  nitric  acid.  Use  is  often  made  of  the  low  solubility  in  water 
and  facility  of  crystallising  to  identify  lactose. 

Milk  sugar  has  a  value  for  [#]D  =  52.7°  and  exhibits  mutarotation  (see 
page  315).  Wiley  uses  [a]D  =  52.53°. 

In  practice  the  estimation  of  milk  sugar  is  required  simply  in  milk 
and  products  such  as  condensed  milk,  whey,  koumiss  and  kefir  derived 
therefrom. 

A  method  which  affords  an  approximate  estimation  of  the  sugar  in 
milk  consists  in  adding  a  few  drops  of  acetic  acid  and  warming,  filter- 
ing from  the  resultant  curd,  boiling,  evaporating  the  clear  whey  to  a 


366  SUGARS. 

small  bulk,  again  filtering,  and  then  evaporating  the  nitrate  to  dry- 
ness.  The  residue,  after  drying  at  130°,  consists  almost  wholly  of  milk 
sugar  and  salts.  The  amount  of  the  former  substance  present  may  be 
ascertained  by  igniting  the  weighed  residue  and  noting  the  loss  of 
weight.  The  amount  of  sugar  thus  obtained  is  always  a  little  too 
high. 

Estimation  of  Milk  Sugar  by  Gravimetric  Methods. — In  esti- 
mating lactose  in  milk  by  Fehling's  solution  it  is  necessary  to  remove 
the  proteins.  This  may  be  done  by  warming  with  a  few  drops  of  acetic 
acid,  filtering,  boiling  the  filtrate  to  coagulate  the  remaining  proteins 
and  again  filtering.  This  filtrate  is  neutralised  before  adding  the  cop- 
per solution.  It  is  better,  however,  to  precipitate  the  proteins  with 
copper  sulphate. 

Soxhlet's  method  adopted  by  the  A.  O.  A.  C.  is  as  follows: 

1.  Preparation  of  the  Milk  Solution. — Dilute  25  c.c.  of  the  milk 
with  400  c.c.  of  water  and  add-io  c.c.  of  a  solution  of  copper  sulphate  of 
the  strength  given  for  Soxhlet's  modification  of  Fehling's  solution,  page 
318,  add  about  7.5  c.c.  of  a  solution  of  potassium  hydroxide  of  such 
strength  that  one  volume  of  it  is  just  sufficient  to  completely  precipitate 
the  copper  as  hydroxide  from  one  volume  of  the  solution  of  copper 
sulphate.     Instead  of  a  solution  of  potassium  hydroxide  of  this  strength 
8.8  c.c.  of  a  half-normal  solution  of  sodium  hydroxide  may  be  used. 
After  the  addition  of  the  alkali  solution  the  mixture  must  still  have  an 
acid  reaction  and  contain  copper  in  solution.     Fill  the  flask  to  the  500 
c.c.  mark,  mix,  and  filter  through  a  dry  filter. 

2.  Estimation. — Place  50  c.c.  of  the  mixed  copper  reagent  in  a 
beaker  and  heat  to  the  boiling  point.     While  boiling  briskly  add  100 
c.c.  of  the  lactose  solution  containing  not  more  than  0.3  grm.  of  lactose 
and  boil  for  6  minutes.     Filter  immediately  through  asbestos  and  deter- 
mine the  amount  of  copper  reduced  by  one  of  the  methods  already 
given  (page  323).     Obtain  the  weight   of  lactose   equivalent  to  the 
weight  of  copper  found  from  the  following  table: 

According  to  Soxhlet,  i  grm.  milk  sugar  in  i  %  solution  reduces 
322.5  c.c.  of  Knapp's  and  214.5  c-c-  °f  Sachsse's  mercurial  reagents. 


LACTOSE. 


367 


TABLE  FOR  THE  ESTIMATION  OF  LACTOSE. 

(Soxhlet-Wein.) 


Milli- 
grams 
of  cop 


Milli- 
grams 
of  lac- 


per.         tose. 


Milli- 

i  grams  e,. ........ 

I  of  cop-  of  lac 
!     per. 


Milli- 
grams 
of  cop- 
per. 


Milli-  Milli- 
grams grams 
of  lac-  of  cop- 

tose.  per. 


Milli-  Milli- 
grams grams 
of  lac-  of  cop- 

tose.  per. 


Milli- 
grams 
of  lac- 
tose. 


100    71  .6 

161 

117.1 

221     l62.7 

28l     209.1 

341    256.5 

101 

72.4 

162 

117.9 

222     163.4 

282     209.9 

342    257.4 

102 

73-1 

163 

118.6 

223     164.2 

283     210.7 

343  •  258.2 

103    73-8 

164 

119.4 

224     164.9 

284    211.  5      344   259.0 

104    74.6 

165  ; 

120.2 

225     165.7 

285    212.3      345 

259-8 

i°S 

75  -3 

166 

120.9 

226 

166.4 

286  j  213.1    346 

260.6 

1  06 

76.1 

167 

121  .7 

227 

167  .2 

287  i  213.9 

347 

261  .4 

107 

76.8 

168 

122  .4 

228 

167  .9 

288   214.7  i 

348 

262  .3 

1  08 

77-6 

169 

123.2 

229   168.6 

289   215.5 

349 

263.1 

109 

78.3 

170 

123.9 

230 

169.4 

290   216.3 

350 

263.9 

no 

79.0 

171 

124.7 

231 

170.1 

291   217.1 

35i 

264.7 

III 

79.8 

172 

125-5 

232 

170.9 

292   217.9 

352 

265-5 

112 

80.5 

173 

126.2 

233 

171.6 

293  •  218.7 

353 

266.3 

H3 

81.3 

174 

127.0 

234 

172.4 

294 

219-5 

354 

267  .2 

114 

82  .0 

175 

127-8 

235 

I73-I 

295 

220.3 

355 

268.0 

US 

82.7 

176 

I28.S 

236 

173-9 

296   221  .  i  ; 

356 

268.8 

116 

83-5 

177 

129.3 

237 

174-6 

297   221.9 

357 

269  .6 

117 

84.2 

178 

I30.I 

238 

175-4 

298  222.7  i 

358 

270.4 

118 

85.0 

179 

130.8 

239 

176.2 

299 

223.5 

359 

271  .2 

119 

85.7 

180 

131  -6 

240 

176.9  I    300 

224.4 

360 

272  .1 

I2O 

86.4 

181 

132.4 

241 

177-7      301 

225.2 

361 

272.9 

121 

87.2 

182 

I33-I 

242 

178.5 

302  225.9 

362 

273.7 

122* 

87.9 

183 

133-9  ! 

243 

179-3 

303 

226.7  ' 

363 

274.5 

123 

88.7 

184 

134-7 

244 

180.1 

304  227.5  ; 

364 

275  -3 

124 
125 

89.4 
90.1 

185 
186 

135-4 
136.2 

245 
246 

180.8 
181.6 

305 
306 

228.3  i 
229.1 

365 
366 

276.2 
277.1 

126 

90.9 

187 

137  -0 

247 

182.4 

307 

229.8 

367 

277-9 

127 

91  .6 

188 

137  -7 

248 

183  .2 

308  230.6 

368 

278.8 

128 

92.4 

189 

138.5 

249 

184.0 

309 

231  -4 

369 

279.6 

129 

93-1 

190 

139-3 

250 

184-8 

310 

232.2 

370 

280.5 

13° 

93-8 

191 

140.0 

251 

185.5 

3" 

232.9 

371 

281.4 

131 

94-6 

192 

140.8 

252 

l86.3 

312 

233-7 

372 

282.2 

132 

95-3 

193 

141  .6 

253 

I87.I 

313 

234-5 

373 

283  .1 

133 

96.1 

194 

142  .3 

254 

187.9 

314 

235  -3 

374 

283-9 

134 
135 

96.9 
97.6 

III 

143-1 
143-9 

25S 
256 

188.7 
189.4 

315 
3i6 

236  .  i 
236.8 

375 
376 

284.8 
285.7 

136 

98.3 

197 

144.6 

257 

190.2 

317 

237.6  ! 

377 

286.5 

137 

99-1 

198 

145-4 

258 

191  .0 

3i8 

238.4  ; 

378 

287.4 

138 

99-8 

199 

146.2 

259 

191  .8 

319 

239.2 

379 

288.2 

139 

100.5 

200 

146.9 

260 

192.5 

320 

240.0 

380 

289.1 

140 

ioi  .3 

201 

147.7 

261 

193-3 

321 

240.7 

38l 

289-9 

141 

102  .0 

202 

148.5 

262 

i94.i 

322 

241  .5 

382 

290.8 

142 

102.8 

203 

149-2 

263 

194.9 

323 

242.3 

383 

291  .7 

143 

103.5 

204 

150.0 

264 

195-7  1    324 

243-1 

384 

292  .5 

144 

104.3 

205 

150.7 

265 

196.4  ;   325 

243-9 

385 

293-4 

145 

105  .  1 

206 

iSi-5 

266 

197.2    326   244.6  i 

386 

294.2 

146 

105.8 

20? 

152.2 

267 

198.0 

327    245.4 

387 

295-1 

147 

1  06  .6 

208 

153-0 

268 

198.8 

328 

246.2  i 

388 

296.0 

148 

107  -3 

209 

153-7 

269 

199-5  !    329 

247.0 

389 

296.8 

149 

108.1 

210 

154-5 

270 

200.3     330 

247.7 

390 

297-7 

ISO 

108.8 

211 

155-2 

271 

201  .1 

331 

248.5 

391 

298.5 

iSi 

109.6 

212 

156.0 

272 

201  .9 

332 

^249.2 

392 

299-4 

IS2 

110.3 

213 

156.7 

273 

202  .7 

333 

250.0 

393 

300.3 

153 

in  .1 

214 

157-5 

274 

203-5 

334   250.8 

394 

301  .1 

IS4 

in  .9 

215 

158.2 

275 

204.3 

335 

251  -6 

395 

302  .0 

ISS 

112  .6 

216 

159-0 

276 

205.1 

336 

252.5 

396 

302.8 

156 

113.4 

217 

159.7 

277 

205-9 

337 

253-3 

397 

303  .7 

157 

114.  1 

218 

160.4 

278 

206  .7 

338 

254-1 

398 

304.6 

158 

114.9     219 

161  .2 

279 

207.5 

339 

254.9 

399    305.4 

159 

II5.6        220 

161  .9 

280  ]  208.3     340   255.7     400  |  306.3 

160   116.4 

368 


SUGARS. 


Estimation  of  Lactose  by  Optical  Methods. — Lactose  may 
be  estimated  by  observing  the  optical  activity  of  its  solution.  To  apply 
this  method  to  milk,  it  is  first  necessary  to  prepare  a  clear  whey  free 
from  other  optically  active  substances.  Precipitation  by  basic  lead 
acetate,  as  has  been  shown  by  Wiley  (Amer.  Chem.J.,  1884,  6,  No.  5), 
does  not  remove  completely  the  laevorotatory  protein  matters;  he  has 
proposed  two  alternative  mercurial  reagents.  His  method,  which  has 
been  adopted  by  the  A.  O.  A.  C.,  is  as  follows: 

a.  Acid  Mercuric  Nitrate. — Dissolve. mercury  in  double  its  weight 
of  nitric  acid,  sp.  gr.  1.42,  and  dilute  with  an  equal  volume  of  water. 
One  c.c.  of  this  reagent  is  sufficient  for  the  quantities  of  milk  men- 
tioned below.     Larger  quantities  may  be  used  without  affecting  the 
results  of  polarisation. 

b.  Mercuric  Iodide  with  Acetic  Acid. — Mix  33.2  grm.  of  potas- 
sium iodide,  13.5  grm.  of  mercuric  chloride,  20  c.c.  of  glacial  acetic 
acid,  and  640  c.c.  of  water. 

Estimation. — The  milk  should  be  at  a  constant  temperature, 
and  its  sp.  gr.  ascertained  with  a  delicate  hydrometer.  When  greater 
accuracy  is  required,  a  pycnometer  is  used. 

The  quantities  of  the  milk  measured  for  polarisation  differ  with  the 
sp.  gr.  of  the  milk  as  well  as  with  the  polariscope  used.  The  quantity 
to  be  measured  in  any  case  will  be  found  in  the  following  table : 


Specific  gravity 

Volume  of  milk  to  be  used 

For  polariscopes  of 
which  the  sucrose 
normal  weight  is 
16  19  grm. 

For  polariscopes  of 
which  the  sucrose 
normal  weight  is 
26.048  grm. 

.024 
.026 
.028 
.030 
.032 
•034 
•035 

c.c. 
60.0 
59  9 
59-8 
59-7 
59-6 
59-5 
59-35 

c.c. 
64.4 
64-3 
64-15 
64.0 

63-9 
63.8 

63-7 

Place  the  quantity  of  milk  indicated  in  the  table  in  a  flask  graduated 
at  102.4  c.c.  for  a  Laurent  or  102.6  c.c.  for  a  Ventzke  polariscope  (Mohr 
c.c.).  Add  i  c.c.  of  mercuric  nitrate  solution  or  30  c.c.  of  mercuric 


LACTOSE.  369 

iodide  solution  (an  excess  of  those  reagents  does  no  harm),  fill  to  the 
mark,  agitate,  filter  through  a  dry  filter,  and  polarise.  It  is  not  neces- 
sary to  heat  before  polarising.  In  case  a  200  mm.  tube  is  used,  divide 
the  polariscope  reading  by  3  when  the  sucrose  normal  weight  for  the 
instrument  is  16.19  grm.  or  by  2  when  the  normal  weight  for  the  in- 
strument is  26.048.  When  a  400  mm.  tube  is  used,  these  divisors  be- 
come 6  and  4,  respectively.  For  the  calculation  of  the  above  table  the 
specific  rotary  power  of  lactose  is  taken  as  52.53°,  and  the  corresponding 
number  for  sucrose  as  66.5°.  The  lactose  normal  weight  to  read  100° 
on  the  sugar  scale  for  Laurent  instruments  is  20.496  grm.;  and  for 
Ventzke  instruments,  32.975  grm.  In  case  metric  flasks  are  used 
the  weights  here  mentioned  must  be  reduced  accordingly. 

In  the  foregoing,  allowance  (2.6  c.c.)  is  made  for  the  volume  of  the 
precipitate.  To  eliminate  the  errors  which  may  arise  in  this  way  Wiley 
and  Ewell  have  applied  Scheibler's  method  of  double  dilution  to  the 
determination  of  lactose.  The  following  is  a  summary  of  the  process: 
For  polarimeters  adapted  to  the  normal  weight  of  26.048  sucrose, 
65.82  grm.  of  milk  are  placed  in  a  100  c.c.  flask  clarified  with  10  c.c. 
of  the  acid  mercuric  nitrate,  the  volume  made  up  to  the  100  mark, 
the  liquid  well  shaken,  filtered,  and  the  rotation  determined.  A  similar 
quantity  of  milk  is  put  into  a  200  c.c.  flask,  acid  mercuric  nitrate 
added  (it  may  be  necessary  to  use  more  than  10  c.c.  in  this  case), 
the  liquid  made  up  to  the  200  c.c.  mark,  shaken,  and  the  rotation 
determined  in  a  100  mm.  tube.  The  true  polarimetric  reading  is  ob- 
tained by  dividing  the  product  of  the  two  readings  by  their  difference. 

H.  D.  Richmond  (Dairy  Analysis)  corrects  for  the  sp.  gr.  and  per- 
centage of  fat  of  the  milk  as  follows :  To  50  c.c.  of  milk  a  quantity  of 
water  is  added  equal  in  c.c.  to  the  sum  of — 

a.  The  degrees  of  gravity  divided  by  20. 

b.  The  percentage  of -fat  divided  by  1.8. 

c.  A  factor  to  convert  scale  readings  into  percentages  of  anhydrous 
sugar.     This  is  5.43  c.c.  if  the  scale  is  in  angular  degrees  and  a  200 
mm.  tube  is  used. 

1.5  c.c.  of  Wiley's  acid  mercuric  nitrate  solution  is  then  added  and 
after  violent  shaking  the  solution  is  filtered  through  a  dry  filter. 

Richmond,  gives  the  following  example:  A  milk  has  a  sp.  gr. 
of  1.032  and  3.60%  of  fat.  (a)  is  32.0/20  =  1.6  c.c.,  (b)  —  3.6/1.8, 
(c)  =  5. 43  c.c.  The  water  added  is  therefore,  1.6+2.0  +  5.43  =  9.03  c.c. 

In  the  case  of  human  milk,  clarification  is  more  difficult  and  a  turbid 
VOL.  1—24 


370  SUGARS. 

filtrate  is  obtained  with  ordinary  precipitating  agents.  Thebault 
(/.  Pharm.  (6),  4,  5)  uses  a  solution  of  picric  acid  10  grm.  in  1000  c.c. 
and  acetic  acid  25  c.c.  in  1000  c.c. 

Estimation  of  Sugars  in  Condensed  Milk. — To  estimate  lactose  in 
condensed  milk,  the  proteins  must  be  removed  by  precipitation  and  the 
reducing  sugar  in  the  whey  determined.  The  cane  sugar  present  may 
be  approximately  estimated  by  difference ;  that  is,  subtracting  the  sum 
of  the  other  ingredients  from  the  total  solids.  The  direct  methods  are 
all  based  on  the  removal  of  the  proteins  and  determination  of  the 
cupric  reducing  or  optical  rotatory  power  before  and  after  inversion. 
This  must  be  effected  by  a  mild  agent,  such  as  citric  acid  or  invertase 
since  mineral  acids  will  also  hydrolyse  the  lactose. 

Stokes  and  Bodner  (Analyst,  1885,  10)  coagulate  the  milk  by  the 
addition  of  i  %  of  citric  acid  without  heating,  dilute,  filter  and  esti- 
mate the  reducing  power  of  the  clear  filtrate.  To  another  portion 
of  the  filtrate  a  further  i  %  of  citric  acid  is  added  and  the  solution 
boiled  for  10  minutes  according  to  the  authors  or  better,  for  at  least  30 
minutes,  according  to  Watts  and  Tempany  (Analyst,  1905,  30,  119). 

The  solution  is  cooled,  neutralised  and  the  reducing  power  again 
determined.  The  increase  is  due  to  the  invert  sugar  formed  from  the 
sucrose. 

Leffmann  and  Beam  use  invertase  for  inversion.  The  proteins  are 
precipitated  by  mercuric  nitrate  and  the  clear  whey  polarised.  In  a 
portion  of  the  filtrate,  the  acid  is  carefully  neutralised,  a  drop  of  acetic 
acid  is  added  and  a  small  quantity  of  invertase  along  with  a  few  drops 
of  an  antiseptic.  The  whole  is  incubated  at  35°  to  40°  for  24  hours. 
After  the  action,  the  proteins  are  precipitated  by  alumina  cream  and 
the  liquid  made  to  known  volume  and  again  polarised.  The  difference 
between  the  two  readings  is  calculated  as  sucrose. 

Bigelow  and  McElroy  (/.  Amer.  Chem.  Soc.,  1893,  15)  propose  the 
following  routine  method  for  the  determination  of  the  sugars,  including 
invert  sugar,  in  condensed  milk.  The  solutions  used  are : 

Acid  Mercuric  Iodide. — See  page  368.     Alumina  Cream. — See  page 

3°9- 

The  entire  contents  of  a  can  are  transferred  to  a  porcelain  dish  and 
thoroughly  mixed.  A  number  of  portions  about  25  grm.  each  are 
weighed  carefully  in  100  c.c.  flasks.  Water  is  added  to  two  of  the  por- 
tions and  the  solutions  boiled.  The  flasks  are  cooled,  clarified  by  means 
of  a  small  amount  of  each  of  the  above  solutions  made  up  to  the  mark, 


LACTOSE.  371 

shaken,  filtered,  and  the  polarimetric  reading  noted.  Other  weighed 
portions  are  heated  in  the  water-bath  to  55°,  one-half  of  a  cake  of  com- 
pressed yeast  added  to  each  flask,  and  the  temperature  maintained  at  55° 
for  5  hours.  The  solutions  are  then  clarified  as  before,  cooled  to  room 
temperature,  made  up  to  100  c.c.,  mixed,  filtered,  and  the  polarimetric 
reading  taken.  The  amount  of  cane  sugar  is  determined  by  the  for- 
mula on  page  313.  Correction  for  the  volume  of  precipitated  solids 
may  be  made  by  the  double-dilution  method.  The  total  reducing 
sugar  is  estimated  by  one  of  the  reducing  methods  on  one  of  the  weighed 
portions  of  the  original  material,  and  if  the  sum  of  it  and  the  amount 
of  cane  sugar  determined  by  the  inversion  method  is  equal  to  that  ob- 
tained by  the  direct  reading  of  both  sugars  before  inversion,  no  invert 
sugar  is  present.  If  the  amount  of  reducing  sugar  seems  too  great, 
the  milk  sugar  must  be  redetermined  as  follows:  250  grm.  of  the 
sample  are  dissolved  in  water,  the  solution  boiled,  cooled  to  80°,  a 
solution  of  about  4  grm.  of  glacial  phosphoric  acid  added,  the  mix- 
ture kept  at  80°  for  a  few  minutes,  then  cooled  to  room  tempera- 
ture, made  up  to  a  definite  volume,  mixed,  and  filtered.  It  may  be 
assumed  that  the  precipitate  produced  by  the  phosphoric  acid  is  equal 
in  volume  to  that  produced  by  the  acid  mercuric  iodide.  Potassium 
iodide  is  then  added  in  amount  not  quite  sufficient  to  neutralise  the  acid, 
and  sufficient  water  to  make  up  for  the  solids  precipitated  by  the  acid. 
The  mixture  is  then  filtered  and  the  filtrate  measured  in  portions  of  100 
c.c.  into  200  c.c.  flasks.  A  solution  containing  20  mg.  of  potassium 
fluoride  and  half  a  cake  of  compressed  yeast  is  added  to  each  flask,  and 
the  mixture  allowed  to  stand  for  10  days  at  a  temperature  of  from  25° 
to  30°.  The  invert  sugar  and  cane  sugar  are  fermented  and  removed 
while  the  milk  sugar  is  unaffected.  The  flasks  are  filled  to  the  mark, 
shaken,  and  the  milk  sugar  determined  by  either  reduction  or  the 
polariscope.  The  amount  of  copper  reduced  by  the  milk  sugar  and 
invert  sugar,  less  the  equivalent  of  milk  sugar  remaining  after  fer- 
mentation, is  due  to  invert  sugar. 

C.  B.  Cochran  (/.  Amer.  Chem.Soc.,  1907,  29,  555-556)  makes  use 
of  Wiley's  acid  mercuric-nitrate  solution  to  invert  sucrose  in  the 
analysis  of  sweetened  condensed  milk.  He  finds  this  inverts  sucrose 
only  very  slowly  at  temperatures  below  15°.  50  c.c.  of  the  solution 
to  be  inverted  (containing  3  c.c.  of  mercuric  solution  per  100  c.c.)  are 
polarised  as  soon  as  possible  after  the  solution  has  been  mixed  at  15° 
and  then  heated  in  boiling  water  for  7  minutes  and  again  polarised. 


37  2  SUGARS. 

The  sucrose  content  in  the  case  of  normal  solutions  is  given  by  the 
formula : 

100  D 

Sucrose  =  —  where   D   is  the  difference   in    polarisation 

132  .68  — o,5/ 

before  and  after  inversion  and  /  =  temperature  above  20°  C.  To 
detect  sucrose  in  condensed  milk  or  milk  sugar,  Leffmann  applies  the 
sesame  oil  test,  i  c.c.  of  sesame-oil,  i  c.c.  of  concentrated  hydro- 
chloric acid  and  0.5  grm.  of  the  sample  are  shaken  together.  The 
characteristic  crimson  colouration  will  be  formed  within  half  an  hour. 
This  test  has  been  found  to  be  satisfactory  and  is  better  than  that 
given  in  United  States  Pharmacopoeia  which  depends  on  carbonisation 
of  the  sucrose  by  strong  sulphuric  acid.  A  rapid  test  for  sucrose  in 
milk  and  cream  consists  in  boiling  a  mixture  of  15  c.c.  of  milk,  o.i  grm. 
of  resorcinol  and  i  c.c.  of  concentrated  hydrochloric  acid.  Sucrose 
gives  a  fine  red  colouration,  pure  milk  remains  almost  unchanged. 


MONOSACCH  ARIDES . 

Of  commercial  importance  are  the  hexoses  C6H12O6,  more  generally 
termed  glucoses,  and  the  pentoses  C5H10O5. 

Glucoses. — Their  generic  and  specific  characters  are  contained  in 
the  table  on  page  287.  Since  they  are  very  closely  related  in  structure, 
differing  indeed,  with  the  exception  of  laevulose,  only  in  the  space 
arrangement  of  the  groups  in  their  molecule,  their  chemical  properties 
are  very  similar.  As  a  class  they  are  (i)  not  susceptible  of  inversion; 
(2)  are  readily  and  directly  fermented  by  yeast;  (3)  are  decomposed  by 
alkalies;  (4)  are  readily  oxidised  by  alkaline  solutions  of  copper. 

Dextrose. — d-Glucose . 

This  is  produced  from  various  polysaccharides  and  glucosides  by 
hydrolysis  with  acids  or  enzymes  and  also  from  cellulose  materials. 
It  is  found  ready  formed  in  various  fruits,  the  proportion  in  grapes  being 
as  high  as  15%.  It  exists  in  two  isomeric  modifications  which  are 
mutually  transformed  into  one  another  in  solution.  The  a-isomeride, 
which  crystallises  from  aqueous  solutions  as  a  hydrate,  forms  tabular 
crystals.  It  is  obtained  in  transparent  prisms  by  crystallisation  from 
hot  methyl  alcohol,  melting  at  146°.  It  is  less  soluble  than  sucrose, 
requiring  11/3  times  its  own  weight  of  cold  water,  It  has  the  value 
MD  =  52-7°>  W;=58.5°  for  the  anhydride  and  exhibits  mutarotation 


DEXTROSE.  373 

(see  page  3 1 5).     The  change  in  rotation  with  the  concentration  (c) 
may  be  calculated  from  the  formula  (Tollens,  Ber.,  1884,  17,  2234): 

[a]D=  +52.5  +  0.018796^  +  0.0005 1 683£2. 

The  rotation  is  constant  from  o  to  100°  C. 

Other  properties  of  dextrose  and  methods  of  estimating  it  have 
been  already  described. 

Characteristic  of  dextrose  (and  glucuronic  acid)  is  the  formation 
of  saccharic  acid  on  oxidation.  5  grm.  of  the  sugar  are  heated  at 
the  temperature  of  the  water-bath  with  30  c.c.  nitric  acid  (sp.gr.  1.15) 
to  a  thick  syrup.  This  is  taken  up  with  water  and  again  evapo- 
rated to  remove  excess  of  acid,  neutralised  with  potassium  car- 
bonate and  a  few  drops  of  acetic  acid  added,  when  the  potassium 
saccharate  crystallises  out  on  standing. 

Characteristic  also  is  the  very  insoluble  phenylosazone,  m.  p.  205- 
210°.  Tutin  gives  this  as  217°  on  recrystallisation  from  pyridine 
(Proc.  Chem.  Soc.,  1907,  23,  50),  but  the  older  value  is  the  correct 
one  (Fischer,  Ber.  1908,  41,  73). 

Dextrose  diphenylhydrazone,  m.  p.  161°,  and  the  methylphenyl- 
hydrazone,  m.  p.  130°,  may  be  used  to  identify  or  detect  dextrose,  par- 
ticularly in  presence  of  pentoses. 

Laevulose. — d-Fructose. — Fruit  Sugar. 

Laevulose  differs  from  dextrose  in  containing  a  ketonic  grouping. 
It  occurs  together  with  dextrose  in  honey  and  many  fruits  and  is  pro- 
duced together  with  dextrose  on  hydrolysis  of  sucrose  or  with  dextrose 
and  other  sugars  on  hydrolysis  of  some  polysaccharides.  Inulin,  a 
polysaccharide  found  in  dahlia  tubers,  yields  laevulose  alone  when 
hydrolysed.  No  glucoside  containing  laevulose  has  been  as  yet  isolated. 
The  principal  physical  and  chemical  properties  of  laevulose  are  contained 
in  the  table  on  page  287.  Its  behaviour  is  very  similar  to  that  of  dex- 
trose, but  it  is  not  readily  crystallisable.  It  yields  glycollic  acid  when 
oxidised  with  bromine  water  and  not  gluconic  acid. 

Laevulose  has  a  value  [a]  JDS  =-93.8°,  which  value  decreases  0.6385° 
for  each  rise  of  i°  C.  in  the  temperature.  The  rotation  at  87.2°  C. 
is  — 52.7°;  that  is  equal,  but  opposite,  to  that  of  dextrose  at  the  same 
temperature. 

This  change  in  the  optical  activity  of  laevulose  affords  a  means  of 
estimating  it  in  presence  of  other  sugars.  The  solution  is  examined 
in  a  jacketed  polarimeter  tube  provided  with  a  thermometer  and  the 


374  SUGARS. 

rotation  noted  at  two  temperatures  as  far  apart  as  possible.  It  is  ad- 
visable to  use  fairly  strong  solutions.  To  calculate  the  number  of  grm. 
of  laevulose  in  100  c.c.  of  solution,  the  difference  between  the  two  tem- 
peratures is  multiplied  by  1.277  and  this  product  divided  into  100  times 
the  alteration  in  rotation  measured  in  circular  degrees  in  a  two  dcm. 
tube  by  sodium  light.  In  view  of  the  fact  that  the  rotatory  power 
of  other  sugars  likewise  differs  with  the  temperature,  this  method 
can  hardly  claim  any  great  accuracy. 

The  respective  reducing  actions  of  dextrose  and  laevulose  on  Fehling's 
copper  solution  are  usually  assumed  to  be  identical.  According  to 
Soxhlet,  however,  the  reducing  action  of  the  former  is  sensibly  greater 
than  that  of  the  latter.  Allihn  states  that  the  reducing  action  of  dex- 
trose and  laevulose  are  identical  if  care  be  taken  to  continue  the  boiling 
of  the  solution  for  half  an  hour. 

Laevulose,  on  account  of  its  ketonic  nature,  reduces  alkaline  copper 
solutions  more  rapidly  than  do  other  sugars  and  at  a  lower  temperature 
and  this  property  may  be  made  use  of  for  its  estimation.  The  sub- 
ject has  of  late  been  fully  investigated  by  J.  Pieraerts  (Bull.  Assoc. 
Chim.  Sucr.  et.  Dist.,  1908,  25,  830),  who  has  made  comparative 
trials  of  a  number  of  reagents.  Excellent  results  were  obtained  with  a 
cupro-glycocoll  solution  (6  grm.  of  cupric  hydroxide,  12  grm.  of 
glycocoll  and  50  grm.  of  potassium  carbonate  dissolved  in  water 
and  made  up  to  1000  c.c.)  which  is  reduced  by  laevulose  at  normal 
temperature  in  12  hours,  but  totally  unaffected  by  other  hexose  or 
pentose  sugars  in  24  hours.  For  the  determination  of  laevulose  in 
commercial  preparations  the  following  general  method  is  prescribed. 
20  to  25  grm.  of  material  are  dissolved  in  150  to  200  c.c.  of  cold 
water,  clarified  with  lead  basic  acetate  and  excess  of  lead  removed  by 
saturated  sodium-sulphate  solution.  After  half  an  hour,  the  solu- 
tion is  filtered  and  diluted  so  as  to  contain  5%  reducing  sugar  and 
tested  for  laevulose  as  above. 

Other  suitable  reagents  are:  Alkaline  cupric  hydroxide  (100  grm. 
of  potassium  carbonate,  50  or  75  grms.  of  potassium  hydrogen  car- 
bonate and  6  grm.  of  cupric  hydroxide  in  1000  c.c.).  With  this 
laevulose  may  be  detected  with  certainty  even  when  much  pentose  is 
present.  The  action  is  continued  for  3  hours  at  the  ordinary  tem- 
perature or,  in  the  absence  of  pentose,  for  i  hour  at  30°. 

i  grm.  laevulose  in  i%  solution  reduces  508.5  c.c.  of  Knapp's 
and  449.5  c-c-  °f  Sachsse's  mercury  reagents.  The  reducing  action 


INVERT    SUGAR.  375 

on  Knapp's  solution  is  about  the  same  as  that  of  dextrose,  but  dextrose 
has  a  considerably  weaker  reducing  action  on  Sachsse's  solution, 
equal  amounts  of  dextrose  and  laevulose  reducing  100  c.c.  and 
148.6  c.c.  respectively. 

According  to  Neuberg,  the  methyl-phenyl-osazone  of  laevulose  is 
very  characteristic.  It  forms  long  yellow  needles,  m.  p.  158  to 
1 60°  C. 

The  following  formula  for  the  estimation  of  laevulose  and  dextrose 
in  mixtures  is  given  by  Pellet  (Bull.  Assoc.  Chin.  Sucr.  Dist.,  1907, 
25,  125-127).  Let  100  grm.  of  the  mixture  contain  x  grm.  of  dextrose 
and  y  grm.  of  laevulose  of  which  p  and  pf  are  the  polarising  values 
compared  with  sucrose  and  r,  rr  the  reducing  powers  compared  with 
invert  sugar.  P  (the  specific  rotation  of  the  mixture)  will  equal  px  + 
p'y,  R  (the  quantity  of  the  reducing  sugars)  will  equal  rx  +  r'y.  Now 
p  =  0.793,  P'  =  I-356J  r  =  0-960,  r'  =  =  1.04  whence  P  =  0.793*  - 
1.356?,  R  =  0.96* +  1.04?. 

I.356R  +  I.Q4P          o.793R-o.96oP 
Therefore  x  =  -  — ,  y  =  — 

2.126  2.126 

Invert  Sugar. — Invert  sugar  exists  largely  in  honey,  molasses, 
and  many  fruits.  It  is  a  mixture  of  equivalent  proportions  of  dextrose 
and  laevulose,  produced  by  the  action  of  heat,  some  enzymes,  acids, 
salts  or  other  agents  on  cane  sugar  and  some  of  its  isomers.  The 
conditions  most  favourable  for  its  formation  have  already  been 
described. 

Invert  sugar  is  an  uncrystallisable  syrup  having  a  sweeter  taste  than 
cane  sugar.  In  its  chemical  reactions  and  optical  properties  it  be- 
haves strictly  as  a  mixture  of  dextrose  and  laevulose.  Invert  sugar 
is  now  made  largely  for  brewers'  use,  being  sold  under  the  names  of 
"invert"  or  "inverse  sugar,"  "saccharum,"  "malt-saccharum;"  and 
other  trade  names.  Starch-sugar  and  cane  sugar  are  often  added. 
The  analysis  of  such  products  may  be  effected  in  the  same  manner  as 
that  of  honey,  but  it  is  generally  sufficient  to  estimate  the  sugar  by 
Fehling's  solution  before  and  after  inversion.  These  estimations  give 
the  data  for  calculating  the  cane  or  uninverted  sugar  and  the  total 
invert  sugar  without  distinguishing  between  the  dextrose  and  laevulose. 
The  small  quantity  of  sucrose  which  is  generally  present  cannot  be 
estimated  accurately  by  double  polarisation. 


SUGARS. 

Analyses  of  Invert  Sugar    (Typical). — From   Moritz  and  Morris' 
"Text-book  of  the  Science  of  Brewing." 
Good.         Inferior. 
Invert  sugar,        75.23  60.53 

Cane  sugar,  0.95  8.56 

Ash,  1.16  5.53 

Proteins,  0.78  1.89 

Water,  19-23  13 .77 

Other  matters,       2.65  9-72 

100.00          100.00 


Galactose. — Galactose  is  formed  together  with  dextrose  by  the 
hydrolysis  of  milk  sugar;  it  occurs  in  some  glucosides,  most  gums  and 
many  plant  products.  It  is  much  less  sweet  than  sucrose,  yields 
dulcitol  on  reduction  and  galactonic  acid  when  oxidised  with  bro- 
mine water. 

It  has  a  value  of  [a]D=  81.27°  f°r  a  I0%  solution  at  15°  and  the 
rotation  at  temperature  /,  and  concentration  c  may  be  caclulated  from 
the  formula : 

[a]D  =  83.137  +  0.199*;  -  (0.276  -  0.0025C)/ 

It  exhibits  mutarotation.  Other  physical  data  will  be  found  on 
page  287 

Characteristic  is  the  o-methylphenylhydrazone  which  forms  colour- 
less needles,  m.  p.  180°,  and  is  sparingly  soluble  in  water  and  abso- 
lute alcohol.  It  may  be  separated  from  dextrose  by  such  yeasts  as 
S.  apiculatus  and  S.  Ludwigii,  which  ferment  dextrose,  but  not  galactose 
(see  page  287).  A  fermentation  test  with  one  of  these  yeasts  affords  a 
very  delicate  means  of  detecting  the  presence  of  small  quantities  of 
in  a  sample  of  galactose.  Commercial  galactose  invariably  contains  a 
small  percentum  of  dextrose. 

Characteristic  of  galactose  and  also  of  lactose  is  the  formation  of 
mucic  acid  on  oxidation  with  nitric  acid. 

For  the  preparation  of  mucic  acid  the  sugar  should  be  slowly  evap- 
orated on  the  water-bath  with  about  4  times  its  weight  of  nitric 
acid  of  1.27  sp.  gr.  or  10  times  its  weight  of  acid  of  1.15  sp.  gr.  until 
a  thick  syrup  is  formed.  This  is  diluted  with  a  little  water  and  al- 
lowed to  stand  for  some  hours.  Mucic  and  oxalic  acid  will  crystallise 


STARCH-SUGAR.  377 

out  and  may  be  separated  by  warm  alcohol  in  which  only  the  oxalic 
acid  dissolves. 

Tollens  (Annalen,  1885,  227,  223)  applies  this  method  quantitatively 
as  follows:  5  grm.  of  the  dry  sugar  are  placed  in  a  beaker  6  cm. 
in  diameter  with  50  c.c.  of  nitric  acid,  sp.  gr  1.15,  and  evaporated  at  the 
heat  of  the  water-bath  to  1/3  of  its  volume.  When  cold  0.5  grm.  of 
pure  mucic  acid  and  100  c.c.  of  water  are  added.  After  i  or,  better,  2 
days'  standing  with  occasional  stirring  the  crystallised  solid  is  collected 
on  a  weighed  filter,  washed  twice  with  5  c.c.  of  cold  water,  dried  at 
100°  and  weighed.  After  subtraction  of  the  0.5  grm.  of  mucic  acid 
added  to  facilitate  crystallisation,  77.4  parts  of  mucic  acid  correspond 
to  100  parts  of  galactose. 

Should  impurities,  such  as  cellulose  or  calcium  salts,  remain  after 
washing,  the  precipitate  and  filter-paper  are  warmed  with  a  solution 
of  ammonium  carbonate,  filtered  and  the  filtrate  evaporated  nearly 
to  dryness  in  a  dish.  The  mucic  acid  is  precipitated  on  the  addition  of 
nitric  acid  and  may  be  collected  and  wreighed. 

This  method  has  proved  useful  in  the  estimation  of  the  galac- 
tose-yielding  groups  in  complex  carbohydrates;  in  presence  of  large 
quantities  of  foreign,  organic  matter,  however,  the  crystallisation  of 
mucic  acid  may  be  hindered  or  altogether  prevented. 

It  has  been  adopted  by  the  A.  O.  A.  C.  for  the  estimation  of  galactan 
the  amount  of  which  is  obtained  by  multiplying  the  weight  of  mucic 
acid  by  1.197. 

Commercial  Glucose— Starch-sugar.— Several  partially  or  fully 
converted  starch-sugars  of  which  dextrose  is  the  leading  constituent 
are  sold  under  the  name  of  glucose,  starch-sugar  and  a  variety  of  other 
more  fanciful  appelations.  Commercial  glucoses  are  very  largely  used 
as  substitutes  for  other  carbohydrates,  e.  g.,  for  malt  in  brewing,  in 
honey  and  for  the  manufacture  of  factitious  wine. 

Starch-glucose  occurs  in  commerce  in  several  forms,  ranging  from 
the  condition  of  pure  anhydrous  dextrose,  through  inferior  kinds  of 
solid  sugar,  to  the  condition  of  a  thick,  syrupy  liquid  resembling  gly- 
cerin, which  contains  a  large  proportion  of  dextrin. 

In  America,  the  term  "glucose"  is  restricted  to  the  syrupy  prepara- 
tions, the  solid  products  being  distinguished  as  "grape  sugar."  The 
following  grades  are  recognised: 

Liquid  Varieties. — Glucose,  mixing  glucose,  mixing  syrup,  corn 
syrup,  jelly  glucose  and  confectioners'  crystal  glucose. 


37$  SUGARS. 

Solid  Varieties. — Solid  grape  sugar,  clipped  grape  sugar,  granulated 
grape  sugar,  powdered  grape  sugar,  confectioners'  grape  sugar,  brewers' 
grape  sugar. 

The  United  States  standard  of  purity  states  that  glucose,  mixing 
glucose  or  confectioners'  glucose  has  a  sp.  gr.  at  100°  F.  of  from 
41°  B  (21  %  water)  tO45°B  (14  %  water)  and  contains  not  more  than 
i  %  ash  on  a  basis  of  41°  B. 

Commercial  starch-glucose  is  produced  by  the  action  of  dilute  acid 
on  starch  or  starchy  matter  or  occasionally  woody  fibre.  In  America 
it  appears  to  be  wholly  made  from  maize  starch,  and  is  often  termed 
"corn  syrup,"  but  in  Europe  rice  and  potato  starches  are  frequently 
used. 

As  a  rule,  in  the  United  States,  hydrochloric  acid  is  the  converting 
agent,  the  proportion  employed  ranging  in  practice  from  i  to  3  % 
according  to  the  kind  of  product  desired  and  the  details  of  the  subse- 
quent manipulation.  The  starch,  or  amylaceous  substance,  is  either 
boiled  with  the  acid  and  water  in  an  open  tank  or  heated  with  it  in 
strong  copper  cylinders  under  high  pressure.  If  the  first  method  be 
adopted  and  the  process  arrested  as  soon  as  a  cold  sample  of  the  liquid 
ceases  to  give  a  blue  colour  with  iodine,  the  product  contains  a  large 
proportion  of  dextrin;  but  if  high  pressure  be  employed  and  the 
action  pushed  further,  dextrose  is  the  chief  product.  In  either  mode 
of  operating,  maltose  and,  very  commonly,  other  products  are  formed 
in  addition  to  dextrose  and  dextrin.  The  acid  is  next  neutralised,  the 
liquid  decolourised,  if  necessary,  by  animal  charcoal  and  evaporated 
in  vacuo  till  it  acquires  a  sp.  gr.  of  1,400  to  1,420. 

When  sulphuric  acid  is  used  as  the  converting  agent  the  product 
retains  a  considerable  quantity  of  dissolved  calcium  sulphate.  Oxalic 
acid  is  also  sometimes  used.  As  a  result  of  the  method  of  manufacture, 
inferior  qualties  of  glucose  may  contain  sulphurous  or  sulphuric  acid, 
calcium  sulphate  or  chlorides,  arsenic  and  lead  compounds.  Arsenic 
may  be  detected  by  Reinsch's  test  or  by  the  methods  referred  to  under 
" Malt";  for  lead  see  p.  569.  The  mineral  matter  may  be  determined 
by  the  weight  and  composition  of  the  ash,  which  should  not  in  a  good 
product  exceed  i  %  and  should  be  almost  wholly  free  from  iron  if  the 
glucose  is  to  be  used  for  brewing.  Sometimes  the  calcium  sulphate  is  re- 
moved by  treating  the  concentrated  solution  with  barium  oxalate.  The 
amount  of  free  acid  is  estimated  by  titration  with  standard  alkali  and 
phenolphthalein;  many  specimens  possess  normally  a  slightly  acid 


STARCH-SUGAR. 


379 


reaction,  probably  due  to  acid  phosphates.  Water  may  be  deter- 
mined by  one  of  the  methods  given  on  page  343,  a  high  temperature 
being  carefully  avoided.  Nitrogenous  matter  is  conveniently  deter- 
mined by  the  Kjeldahl  process  or  by  ignition  with  soda-lime. 

Most  commercial  starch-sugars  contain,  in  addition  to  dextrose  and 
dextrin,  maltose  and  a  notable  percentage  of  unfermentable  carbo- 
hydrates, apparently  produced  by  overtreatment  with  acid.  The  term 
gallisin  is  applied  to  these. 

The  majority  of  the  published  analyses  of  glucose  products  have 
failed  to  take  all  these  products  into  account  or  are  based  on  faulty 
methods  of  analysis.  In  consequence,much  confusion  exists  on  this 
particular  subject. 

Gallisin  as  hitherto  obtained  is  not  a  definite  compound  and  it  appears 
advisable  only  to  retain  the  term  as  synonymous  with  unfermentable 
matter.  The  whole  question  of  the  structure  of  starch,  the  nature  of 
the  various  dextrins  and  of  isomaltose  still  remains  a  vexed  question  in 
carbohydrate  chemistry  and  the  utmost  confusion  exists  as  regards 
the  subject.  (The  reader  is  referred  to  Ling's  article  on  Starch  in 
Sykes'  ''Text-book  of  Brewing/'  edition  1907.) 

The  following  analyses  of  commercial  glucoses,  quoted  by  W.  G. 
Valentin  (Jour.Soc.  Arts,  24,  404)  are  amongst  the  most  complete  and 
probably  most  reliable  hitherto  published: 


No. 

I. 

No. 

2. 

No. 

3- 

No. 

4- 

No 

5- 

Dextrose  
Maltose  

80.00 
none 
none 

8.20 

i  .30 
10.50 

58.85 
14.11 

1.70 

9-38 
1.40 

I4.56 

67.44 
10.96 
none 

4-3° 
i  .60 

I5-70 

63.42 

I3-50 
none 

8.40 
1.50 
13.18 

61.46 
13.20 
none 

8.60 
i  .60 
15  .20 

Dextrin  

Unfermentable  carbohydrates 
with  a  little  protein  matter  .  .  . 
Mineral  matter 

Water 

Total  solid  matter  

100. 

00 

IOO 

00 

IOO 

OO         IOO 

00 

IOO 

.06 

89. 
80. 

5°       85.44 
oo       74.66 

84 
78 

3° 
40 

86 
76 

82 
92 

84 
74 

.80 
.60 

Matter  of  use  to  the  brewer.  .  . 

No.  i  was  somewhat  brown,  very  hard,  and  of  English  manufacture. 
No.  2  was  pale  straw-coloured,  softish,  French.     No.  3,  whitish,  some- 


t8o 


SUGARS. 


what  hard,  English.     No.  4,  whitish,  somewhat  hard  German.     No. 
5,  white,  somewhat  hard,  German. 

The  following  analyses  are  by  I.  Steiner  (Dingier' s  Polyt.  Jour.,  233, 
262): 


No. 

i. 

No. 

2. 

No. 

3.           No 

4- 

Dextrose  
Maltose 

45-40 
28.00 

9-3° 
1.50 
traces 

.08 

•3° 
15.50 

26. 
40. 

i  . 

I. 

50 

90 

00 

80 

03 
50 

oo 

76 

5 

5 
J3 

.00 

.00 

•30 

.20 

•05 
.40 

42 

39 

i 
7 

.60 

.80 

.10 

.60 

Dextrin                                           .  . 

Unfermentable  carbohydrates.  .  . 
Proteins                 

Free  acid  (as  H2SO4)  
Mineral  matter  
Water 

Total  solid  matter         .          .... 

100.08 

100. 

03 

IOO 

25 

IOO 

.00 

84 
82 

42 

70 

82! 

97 

70 

86 
81 

65                  92 

oo           82 

.40 
.40 

Matter  of  use  of  the  brewer 

No.  i  was  of  German  origin,  white  and  soft.  The  other  samples 
were  English,  and  made  from  maize  without  previous  separation  of  the 
starch. 

These  analyses  are  unusually  elaborate,  and  for  commercial  purposes 
there  is  no  occasion  to  enter  so  much  into  detail.  Many  analysts 
limit  their  statements  to  the  proportions  of  water,  ash,  dextrin,  and 
glucose,  ignoring  the  maltose  altogether.  This  practice  is  very  objec- 
tionable, as,  in  an  analysis  so  stated  not  only  is  the  maltose  classed  as 
dextrose,  but  the  amount  of  dextrin  is  also  seriously  in  error.  Never- 
theless, the  cupric  reducing  power  of  the  sample  is  a  character  of 
•considerable  value  for  the  commercial  classification  of  a  glucose  or  for 
assaying  a  sample  during  the  process  of  conversion,  provided  its  true 
meaning  be  not  misinterpreted.  Taken  together  with  the  specific 
rotatory  power  of  a  sample,  and  the  percentage  of  ash  and  water,  it 
often  affords  ample  information  for  commercial  purposes. 

The  following  data  allow  the  relative  proportions  of  dextrose,  mal- 
tose and  dextrin  in  a  sample  of  glucose  to  be  deduced.  The  total  solids 
are  ascertained  from  the  solution  gravity  or  by  carefully  drying  the 
sample,  and  the  residue  is  ignited  to  ascertain  the  ash.  The  difference 
gives  the  organic  solids  (O).  The  reducing  power  (K)  and  the 
specific  rotatory  power  (S)  of  the  sample  are  further  determined. 


STARCH-SUGAR.  381 

Then  if  m  be  the  percentage  of  maltose,  g  that  of  dextrose  and  d  that 
of  dextrin  in  the  sample 

—  K) 


zoo 

g=  K  —  0.62;;? 
d  =  0—  (g  +  m) 

Defects  of  the  method  are  that  K  and  S  have  to  be  ascertained 
very  accurately  and  that  the  presence  of  unfermentable  bodies,  such  as 
gallisin,  which  exert  a  reducing  action,  is  ignored. 

Wiley  bases  a  process  on  the  assumption  that  dextrose  and  maltose 
are  oxidised  to  optically  inactive  products  when  heated  with  excess 
of  an  alkaline  solution  of  mercuric  cyanide  and  that  dextrin  is  un- 
affected. The  following  is  the  mode  of  operation  adopted  by  Wiley 
(Chem.  News,  1882,  46,  175)' 

a.  The  cupric  reducing  power  of  the  sample  is  ascertained  in  the 
usual  way  by  Fehling's  solution. 

b.  The  specific  rotatory  power  is  a  scertained  by  polarising  a  10% 
solution  (previously  heated  to  boiling)  in  the  ordinary  manner. 

c.  10  c.c.  of  the  solution  employed  for  &  (  =  i  grm.  of  the  original 
sample)  is  treated  with  an  excess  of  an  alkaline  solution  of  mercuric 
cyanide,1    and   the   mixture  -boiled   for   2  or  3  minutes.     It  is  then 
cooled  and  slightly  acidified  with  hydrochloric  acid,  which  destroys 
the  reddish-brown  colour  possessed  by  the  alkaline  liquid.     The  solu- 
tion is  then  diluted  to  50  c.c.,  and  the  rotation  observed  in  a  tube  4  deci- 
metres in  length.     The  angular  rotation  observed  will  be  due  simply 
to  the   dextrin,  the  percentage  of  which  in  the  sample  may  be  calcu- 
lated by  the  following  formula:2 

The  percentages  of  dextrose  and  maltose  may  be  deduced  from 
the  reducing  power  of  the  sample,  or  from  the  difference  between  the 

JThe  mercuric  solution  is  prepared  by  dissolving  about  120  grm.  of  mercuric  cyanide 
and  the  same  quantity  of  sodium  hydroxide  in  1000  c.c.  and  filtering  the  liquid  through 
asbestos.  20  c.c.  of  this  solution  should  be  employed  for  samples  having  K  less  than  65 
per  cent.,  and  25  c.c.  when  the  reducing  power  is  greater  than  this.  In  all  cases  care  must 
be  taken  to  use  a  slight  excess  of  the  mercuric  solution,  which  may  be  ascertained  by  holding 
a  piece  of  filter-paper  with  a  drop  of  the  solution  on  it  over  fuming  hydrochloric  acid,  and 
then  over  ammonia  or  hydrogen  sulphide  water,  when  a  dark  stain,  due  to  mercuric  sul- 
phide, will  appear  on  the  paper. 

2If  the  directions  in  the  text  are  adhered  to,  and  a  sample  shows  an  angular  rotation  of 
3.2°  with  a  tube  4  decimetres  in  length,  then  the  calculation  will  be: 
3.2X1000X50  m     ,  , 

X98X40X!       =*o.2o%  of  dextrin.      - 
Circular  rotation  X  1000  X  vomme  in  c.c.  of  solution  polarized 

=     Percentage  of  dextrin. 

198  X  length  of  tube  in  centimetres  X  weight  of  sample  in 
solution  employed  for  mercury  treatment. 


382  SUGARS. 

specific  rotatory  power  before  (S)  and  after  (s)  the  treatment  with  the 
alkaline  mercuric  solution.  Using  the  same  symbols  as  before,  with 
the  addition  of  u  for  the  unknown  and  presumed  inactive  organic 
matter,  the  following  equations  result : 


=g  +  m  +  d  +  u;  K  =  i.oo  g  +  o.62m. 
=  0.527,^  +  1.392^  +  1.98^;  5  =  1.986?. 


From  these  data: 


S  — 5  =  0.527^  +  1.3927^;  and  o.527K  =  o.527gr  +  o.32674w;  whence 

S  —  s—  o.527K 
i.oo52ow  =  S  —  s  —  O.527K;  m  = 

The  proportions  of  dextrose,  dextrin,  and  inactive  carbohydrates  are 
deduced  by  means  which  are  evident. 

In  Wiley's  process  it  is  assumed  that  the  indefinite  carbohydrates  have 
no  optical  activity  and  no  reducing  action  on  Fehling's  solution. 
Both  these  assumptions  are  probably  incorrect,  in  addition  to  which  it 
has  not  been  definitely  proved  that  boiling  with  an  alkaline  solution  of 
mercuric  cyanide  wholly  destroys  the  optical  activity  of  maltose  and 
dextrose,  while  leaving  that  of  dextrin  unchanged.  Nor  has  the 
action  of  the  mercuric  solution  on  the  indefinite  carbohydrates  been 
ascertained  with  certainty,  though  they  may  be  presumed  to  react 
.like  maltose,  since  "gallisin"  is  stated  to  reduce  Knapp's  solution. 

It  is  manifestly  impossible  to  determine  with  absolute  accuracy  the 
amount  of  commercial  glucose  added  as  an  adulterant  by  reason  of 
the  differing  amounts  of  dextrose,  maltose  and  dextrin  present  in  com- 
mercial glucose. 

When  the  amount  of  invert  sugar  present  is  very  small  an  approxi- 
mate result  is  obtained  on  the  assumption  that  commercial  glucose 
polarises  +175°  V. 

The  formula  g  =  (a  —  5)100/175  is  used  when  g=  %  of  commercial 
glucose,  a  =  direct  polarisation,  s=%  of  sucrose. 

In  substances  which  consist  largely  of  invert  sugar  much  more 
accurate  results  are  attained  by  polarising  at  87°  in  a  water- jacketed 
tube  an  inverted  half-normal  solution  of  the  sample  (13  grm.)  prepared 
as  described  elsewhere  with  the  following  exceptions:  After  inversion, 
cool,  add  a  few  drops  of  phenolphthalein  and  enough  sodium  hydroxide 
to  neutralize;  discharge  the  pink  with  a  few  drops  of  dilute 
hydrochloric  acid,  add  from  5  to  10  c.c.  of  alumina  cream,  and  make 
up  to  the  mark  and  filter.  Multiply  by  2  the  reading  at  87°  in  the 


HONEY.  383 

200  mm.  tube;  multiply  this  result  by  100  and  divide  by  the  factor 
163  to  express  the  glucose  in  terms  of  glucose  polarising  175°  Ventzke. 

HONEY. 

Ordinary  honey  is  a  saccharine  substance  collected  and  stored  by  a 
particular  species  of  bee  (Apis  melliftca). 

Honey  is  essentially  a  concentrated  aqueous  solution  of  certain 
sugars,  dextrose  and  laevulose  being  the  chief  constituents.  In  some 
cases  small  amounts  of  sucrose  are  present  and  also  a  sensible  quantity 
of  the  alcohol  mannitol.  Honey,  particularly  when  of  coniferous 
origin,  also  sometimes  contains  some  quantity  of  a  carbohydrate  in- 
termediate between  starch  and  sugar  which  is  precipitated  by  strong 
alcohol.  These  are  termed  honeydew  honeys  in  America.  The  other 
constituents  are  water,  formic  and  other  organic  acids  and  other 
small  proportions  of  mineral  and  flavouring  matters,  wax  and 
debris  in  the  form  of  pollen,  insects'  wings,  etc.  Not  infrequently 
alkaloidal  and  bitter  principles  derived  from  the  pollen  are  also  met 
with. 

Genuine  honey  should  contain  not  more  than  8%  sucrose,  25% 
water  and  0.25%  ash.  It  should  contain  dextrose  and  laevulose  in 
about  equal  proportions  and  be  laevorotatory.  Honey  of  coniferous 
origin,  however,  gives  genuine  dextrorotatory  samples. 

Although  the  figures  representing  the  other  constituents  show  con- 
siderable range,  the  great  majority  of  samples  of  honey  are  of  a  re- 
emarkably  constant  character,  the  glucoses  ranging  from  70  to  80%, 
the  water  from  17  to  20%,  and  the  ash  from  o.io  to  0.25%.  In 
normal  honey  the  dextrose  and  laevulose  are  present  in  approxi- 
mately equal  proportions,  but  if  the  honey  has  crystallised  in  the  comb 
the  runnings  therefrom  will  be  deficient  in  dextrose,  and  hence  will  be 
strongly  laevorotatory.  It  is  held  by  experienced  bee-keepers  that  all 
genuine  honey  will  eventually  crystallise,  and  hence  that  honey  war- 
ranted to  remain  syrupy  is  probably  adulterated. 

The  composition  and  analysis  of  American  honeys  has  been  recently 
very  fully  studied  by  C.  A.  Browne  (Bulletin  no),  who  has  investigated 
the  general  composition  of  honeys  with  particular  reference  to  the 
effects  of  different  floral  nectars.  He  gives  the  following  average 
analyses  of  99  samples.  The  table  also  includes  the  average  of  recent 
analyses  of  European  honeys  by  Konig  (Chem.  Nahrungs-  und  Genuss- 


SUGARS. 


mittel,  3d  edition) — 138  samples — and  by  Lehman  and  Stadlinger — 
17  samples  (Zeit.  Nahr.  u  Genussm.,  1907,  13,  397). 


Lehman 

Browne 

Konig 

and 

Stadlinger 

III 

||1 

||| 

a 
a 

a 

3 

a 

1 

S  C  nJ 
O  O  OT 

0  o  rt 

g  £$ 

'S 

X 

o 

ftj        O^ 

•g      ^ 

•^  c  °* 

a 

§ 

< 

O 

H-3 

Q 

•« 

Water  
Invert  sugar  
Sucrose 

17.7 

75- 
i  9 

16.1 
67. 

I7.6 

74-4 

2   O 

I  0.0 

54- 

33-6 
91.58 
129 

20.  6 

73-1 
1.76 

19.3 
73-45 

Ash  
Undetermined  .  .  . 

0.18 

3-7 

0.81 

3-4 

0.23 

3-7 

Q.  02 

0.68 

0.25 

0.09 

4.07 

Free  acid  as  formic 

0.08 

0.12 

0.09 

0.07 

The  following   figures   give   the   average   composition   of   genuine 
(Canadian?)  honey  (Canadian  Dept.  In.  Rev.;  Bui.,  47): 


Sucrose  (by  Clerget), 
Dextrose  and  laevulose, 
Water, 
Ash, 


0.5  to  7 . 64  per  cent, 
66.37  to  78.80  per  cent. 
12.0  to  33  .00  per  cent, 

0.03  to    0.50  per  cent. 


Analysis  of  Commercial  Honey. — The  common  adulterants  of 
honey  are  starch-sugar,  invert  sugar,  cane  sugar,  and  molasses. 

The  proportion  of  water  in  honey  may.be  determined  as  in  molasses 
(page  356),  or  by  the  method  of  Wiley,  described  on  page  353.  A  use- 
ful check  on  the  result  is  obtained  by  calculating  the  solids  from  the 
density  of  a  20%  solution  of  the  sample,  as  described  on  page  290. 

The  ash  of  genuine  honey  is  usually  very  trifling  in  amount.  If  in 
excess  of  0.3%,  it  should  be  tested  for  calcium  sulphate,  the  presence 
of  which,  in  notable  quantity,  is  an  almost  certain  indication  of  adul- 
teration by  starch  glucose  or  invert  sugar.  Sulphates  may  also  be  de- 
tected by  the  direct  addition  of  barium  chloride  to  the  aqueous 
solution  of  the  sample.  A  high  ash  containing  a  notable  proportion 
of  chlorides  points  to  a  probable  adulteration  with  molasses. 

The  insoluble  matter  of  honey  may  be  ascertained  as  in  sugar. 
It.  usually  consists  of  wax,  pollen  and  some  minor  organised  materials, 
and  should  be  carefully  examined  under  the  miscrocope.  Starch, 
which  is  not  a  normal  constituent  of  honey,  will  be  readily  recognised  in 


HONEY. 


385 


the  residue  by  its  reaction  with  iodine,  and,  if  present  in  quantity,  points 
to  an  adulteration  of  the  sample  with  flour  or  other  farinaceous  sub- 
stance, the  exact  nature  of  which  will  be  indicated  by  its  microscopic 
appearance. 

Gelatin,  if  present,  will  be  left  undissolved  on  treating  the  sample 
with  spirit,  and  will  be  recognised  by  its  odour  on  ignition,  and  the  re- 
action of  its  aqueous  solution  with  tannin. 

Dextrin,  which  is  not  found  in  genuine  honey,  but  is  a  constituent 
of  commercial  starch-sugar,  may  be  detected  by  diluting  the  honey 
with  an  equal  measure  of  water,  and  gradually  adding  strong  spirit, 
stirring  constantly  until  a  permanent  turbidity  is  produced.  In  sam- 
ples adulterated  with  starch-sugar  a  heavy  gummy  deposit  will  soon 
form,  but  with  genuine  honey  only  a  slight  milkiness  is  produced. 

Saccharine  additions  to  honey  can  only  be  detected  by  a  careful  ex- 
amination of  the  action  of  the  sample  on  polarised  light,  and  its  behav- 
iour with  Fehling's  and  other  reducible  solutions.  The  following  table 
shows  the  specific  rotatory  power  and  cupric  reducing  power  of  mix- 
tures of  cane  and  invert  sugar,  containing  82%  of  the  solid  and  18% 
of  water,  and  of  average  starch-sugar  syrup,  as  compared  with  genuine 
honey.  The  table  also  shows  the  changes  produced  in  solutions  of  the 
above  saccharine  matters  by  the  action  of  invertase  (page  314),  by  pro- 
longed heating  with  dilute  acid  (page  296),  and  by  fermentation  with 
yeast  (page  298) : 


Cane  sugar     Invert  sugar ,        Average  r  ««„;»,« 

82%,  .  82%,  _          starch-sugar,          genuine 


water   18% 

water  18%    |           syrup 

Specific  Rotatory  Power  for 

Sodium  Ray: 

Original  substance. 
After  treatment  with  invertase, 

+  54-5 
—  19.9  at  15° 

—  18.9  at  15° 
—  18.9  at  15° 

+92  to  ioo 
little  altered 

+2  to  —3 
little  altered 

After  prolonged  heating  with 

dilute  acid. 

—19.9  at  15° 

—  18.9  at  15° 

+45 

little  altered 

After  fermentation  with  yeast, 

inactive 

C 

inactive   | 

very  notably 
dextrorotatory 

J     OtO  +  4 

Cupric  Reducing  Power: 

Original  substance, 

.0 

82 

53 

61  to  82 

After  treatment  with  invertase, 

86.3 

82 

little  altered 

little  altered 

After   prolonged   heating  with 

dilute  acid, 

86.3 

82 

82 

little  altered 

After  fermentation  with  yeast, 

.0 

0 

very  notable 

o  to  2    - 

Invert  Sugar. — According  to  the  table,  there  is  a  sensible  differ- 
ence  between   the  rotation  of   invert  sugar  and  genuine   honey,  but 
unfortunately  this  distinction  does  not  always  hold  good,  for  if  the 
honey  has  crystallised  in  the  comb  some  of  the  dextrose  is  apt  to  re- 
VOL.  1—25 


386  SUGARS. 

main  there,  and  the  honey  drained  therefrom  will  contain  excess  of 
liuvulose,  and  be  more  strongly  laevbrotatory  than  is  indicated  by  the 
figures  in  the  table.  Unless,  therefore,  the  ash  be  excessive,  or  happen 
to  contain  calcium  sulphate,  the  positive  recognition  of  added  invert 
sugar  by  such  means  is  impossible. 

The  artificial  honey  made  by  Herzfeld's  method  (Zeits.  Ver.  d. 
Zucker  Ind.,3it  1988),  which  consists  in  heating  1,000  grm.  of  refined 
sugar  with  300  c.c.  of  water  and  i.i  grm.  of  tartaric  acid  to  boiling 
for  30  to  45  minutes,  has  a  rich  golden-yellow  colour  and  a  mild,  pleasant 
flavour.  On  analysis,  but  for  a  deficiency  in  ash,  it  gives  values  agreeing 
very  closely  with  those  recorded  for  pure  honeys. 

To  detect  the  presence  of  added  invert  sugar  it  is  necessary  to  have 
resource  to  colorimetric  tests.  C.  A.  Browne  (Bulletin  no)  uses  ani- 
line acetate  which  gives  a  red  or  pink  tint  with  furfuraldehyde  pro- 
duced at  the  high  temperature  of  inversion  by  the  Herzfeld  and  other 
processes,  but  no  colouration  with  pure  honey.  The  reagent  is  freshly 
prepared  each  time  before  use  by  shaking  5  c.c.  aniline  with  5  c.c. 
water  and  enough  glacial  acetic  acid  (2  c.c.)  to  just  clear  the  emulsion, 
i  to  2  c.c.  of  the  reagent  are  allowed  to  flow  down  the  walls  of  a  test- 
tube  onto  5  c.c.  of  a  solution  of  the  honey  in  an  equal  weight  of 
water.  If  after  gentle  shaking  a  red  ring  forms  below  the  aniline 
layer  and  gradually  spreads  to  the  whole  solution,  invert  sugar  is 
present. 

Fiehe  (Chem.  Zeit.,  1900,  32,  1045)  describes  the  following  method* 
The  ethereal  extract  of  artificial  honeys  on  evaporation  gives  an  intense 
red  colouration  with  resorcinol  hydrochloric  acid  (i  part  of  resorcinol 
and  100  parts  of  hydrochloric  acid,  sp.gr.  1.19).  This  is  due  to  decom- 
position products  of  laevulose  formed  by  heating  invert  sugar  with 
acids  during  the  manufacture.  Natural  honey  which  has  not  been 
heated  with  acid  never  gives  the  reaction,  nor  does  glucose,  galactose, 
milk-sugar,  or  maltose.  The  ammoniacal  silver  test  of  Ley  (Pharm. 
Zeit.,  1902,  47,  603)  consists  in  heating  absolution  of  the  honey  with  a 
small  quantity  of  silver  oxide  dissolved  in  ammonia.  Clear  honeys 
give  a  brownish  colour  and  leave  a  yellowish-green  on  the  surface  of 
the  glass.  Honey  substitutes  appear  a  dirty  brown  or  black  and  give 
no  greenish  after-hue. 

Cane  Sugar. — -Any  considerable  proportion  of  cane  sugar  in 
honey  would  be  indicated  by  the  strong  dextro-rotation  of  the  sample, 
changed  to  left-handed  rotation  on  treatment  with  invertase  or  dilute 


HONEY.  387 

acid.  The  proportion  of  cane  sugar  can  be  estimated  from  the  extent 
of  the  change  in  the  rotatory  and  reducing  power  of  the  sample 
caused  by  treatment  with  invertase,  or,  in  the  absence  of  starch- 
sugar,  by  inversion  with  dilute  hydrochloric  acid,  as  on  page  313. 
As  already  stated,  a  small  percentage  of  sucrose  appears  sometimes  as 
a  constituent  of  genuine  honey.  For  calculating  the  percentage  of 
sucrose,  Lehmann  and  Stadlinger  Zeit.  Nahr.  u.  Genussm.,  1907,  13, 
397-413)  give  the  formula: 

Per  cent,  sucrose  =MDX  1.1448  in  which  [a]D  is  the  difference  in 
the  specific  rotatory  power  before  and  after  inversion. 

Starch -sugar  is  still  more  dextrorotatory  than  cane  sugar  to  com- 
mence with,  the  optical  activity  falling  to  about  one-half  by  prolonged 
treatment  with  acid,  while  the  products  left  after  fermentation  are  still 
notably  dextrorotatory.  In  the  absence  of  added  cane  and  invert 
sugar,  an  approximate  estimation  of  the  proportion  of  starch  syrup 
in  honey  may  be  made  by  reckoning  i%  of  the  adulterant  for  every 
degree  of  dextrorotatory  power  possessed  by  the  original  sample.  Of 
course,  it  must  not  be  forgotten  that  a  dextrorotation  of  a  few  degrees 
degrees  is  observable  in  genuine  coniferous  honey  dew  honey. 

E.  Beckmann  (Zeit.  anal.  Chem.,  1896,  263)  tests  honey  for  the  addi- 
tion of  starch-sugar  by  means  of  methyl  alcohol  which  produces  no  pre- 
cipitate with  genuine  honeys,  including  both  the  ordinary  form  and  the 
dextrorotatory  variety.  When  starch-sugar  is  present  there  is  a 
marked  precipitate  which  should  give  the  characteristic  red  colouration 
of  erythrodextrin  with  iodine.  The  test  has  been  extended  so  as  to  apply 
also  to  solid  starch-sugar  as  follows:  5  c.c.  of  a  20%  solution  of 
of  honey  in  water  are  mixed  with  3  c.c.  of  2%  barium  hydroxide 
solution  and  17  c.c.  of  methyl  alcohol  and  the  mixture  is  well  shaken. 
Pure  honey  remains  clear,  but  the  above  adulterants  cause  a  consider- 
able precipitate.  Methyl  alcohol  of  high  purity  must  be  used. 

This  method  has  been  applied  quantitatively,  but  is  of  doubtful  accu- 
racy in  such  cases.  However,  it  does  enable  the  analyst  even  under 
unfavourable  conditions  to  recognise  the  addition  of  small  quantities 
of  dextrin,  starch-sugar  or  its  syrup  to  conifer  honey  containing  as  much 
as  4  per  cent,  of  natural  dextrinous  matter.  (This  subject  is  dealt  with 
in  more  detail  in  Leffmann  and  Beam's  Food  Analysis.) 

According  to  Leffmann  and  Beam,  a  common  method  of  adultera- 
tion consists  in  pouring  starch-sugar  syrup  over  honey-comb  from 
which  the  honey  has  been  already  drained.  On  standing  such  a  mix- 


SUGARS. 


ture  acquires  a  honey  flavour;  it  will  give  a  high  dextrorotatory  polarisa- 
tion hardly  altered  on  hydrolysis. 

The  dextrin-like  body  in  coniferous  honey  has  been  shown  by  Konig 
and  Hermann  (Zeit.  Nahr. -Genus  sm.,  1907,  13,  113  to  132)  to 
differ  from  dextrins  prepared  from  starch  by  malt  extracts  or  acids. 
It  is  fermented  by  beer  yeasts. 

The  reliable  points  in  the  differentiation  of  honey- dew  honeys  and 
those  adulterared  with  glucose  are  (a)  the  difference  in  invert  polarisa- 
tion between  20°  and  87°  (corrected  to  77%  of  invert  sugar);  (b) 
the  reaction  of  the  honey  and  its  precipitated  dextrin  toward  iodine; 
(c)  the  polarisation  of  the  inverted  solution  after  precipitation  of 
the  dextrin  with  absolute  alcohol.  This  process  due  to  Konig  and 
Karsch  (Zeit.  anal.  Chem.  1895,  34,  i)  depends  on  the  fact  that  after 
precipitating  the  dextrins  and  inverting  natural  honeys  will  show  a 
laevorotation,  honeys  with  25%  or  more  of  glucose  a  dextrorotation. 

NOTE. — To  do  this  the  difference  in  invert  polarisation  between  20°  and  87°  is  multiplied 
by  77,  the  average  percentage  of  invert  sugar  in  pure  honey,  and  this  product  divided  by 
the  percentage  of  invert  sugar  after  inversion  found  in  the  sample.  To  find  the  percentage 
of  pure  honey  in  the  sample  this  quotient  is  multiplied  by  100  and  divided  by  26.7. 

MAPLE  PRODUCTS. 

Maple  Syrup1  and  Maple  Sugar  are  products  of  considerable  im- 
portance in  the  United  States,  but  have  not  yet  come  to  England  in 
any  quantity.  They  contain  sucrose  with  minute  amounts  of  special 
flavours  and  are  frequently  adulterated  with  sucrose  from  other  sources 
or  starch-sugar.  The  latter  is  detected  by  polarimetric  examination 
before  and  after  hydrolysis  when  pure  maple  sugar  is  inverted  and  has 
a  negative  rotatory  power,  glucose  is  but  slightly  affected. 

Leffmann  and  Beam  quote  the  following  results  obtained  by  Ogden: 


Polarimeter  reading 

Per  cent. 

Direct 

After 
hydrolysis 

sucrose 

Maple  syrups  free  from  glucoses, 

53  -1 
59  -6 

22.  2 
—21-9 

56.0 
60.6 

Maple  sugars, 

84.1 
88.0 

—28.8 
-28.3 

85-9 
87.6 

Maple  syrups  containing  glucoses, 

80.0 

IOO.O 

+  I8.Q 

+  45-6 

1  Maple  Syrup  is  defined  to  contain  not  more  than  32%  of  water  and  not  less 
than  0.45%  of  ash. 


MAPLE    PRODUCTS.  389 

Pure  maple  syrup  gives  an  abundant  fiocculent  precipitate  with 
methyl  alcohol  which  does  not  adhere  to  the  glass.  When  much  starch- 
sugar  is  present  a  more  granular  precipitate  is  obtained  which  adheres 
to  the  glass. 

Leach  (Bulletin  65)  finds  that  the  grade  of  starch-sugar  syrup 
commonly  used  to  adulterate  maple  syrup,  honey,  molasses,  etc.,  has 
a  value  [^=87.5  with  a  half-normal  weight  in  a  2  dm.  tube.  He 
calculates  approximately  the  amount  present  (G)  from  the  formula 
G  =  0.561  (a  —  S),  in  which  S=  sucrose  and  a  the  polarimeter  reading 
before  hydrolysis.  The  sucrose  is  determined  in  the  usual  manner  by 
the  change  in  rotation  on  hydrolysis. 

To  judge  the  addition  of  sucrose  the  amount  and  alkalinity  of  the 
ash  are  carefully  determined,  also  the  amount  of  basic  lead  acetate 
precipitate  and  the  malic  acid  value.  The  ash  should  not  be  less 
than  0.625  of  the  total  sucrose;  it  should  be  determined  by  burning 
in  a  muffle  at  a  low  temperature  as  some  of  the  constituents  are  vola- 
tile; it  is  also  deliquescent  and  must  be  weighed  quickly.  The 
alkalinity  of  the  water-soluble  portion  to  phenolphthalein  and  methyl- 
orange  and  of  the  insoluble  portion  can  be  determined  in  the  usual 
manner. 

The  malic-acid  value  is  obtained  as  follows:  6.7  grm.  of  the  sample 
are  diluted  with  water  to  20  c.c.,  the  solution  made  slightly  alkaline 
with  ammonium  hydroxide,  i  c.c.  of  10%  calcium  chloride  solution 
and  60  c.c.  of  95%  alcohol  added  and  the  beaker  covered  and  heated 
an  hour  on  the  water-bath.  After  standing  overnight,  the  precipitate 
is  filtered  through  a  hardened  filter-paper,  washed  with  75%  alcohol 
to  remove  all  calcium  chloride,  dried  and  ignited.  20  c.c.  N/io 
hydrochloric  acid  are  added,  the  lime  dissolved  by  warming  the  solu- 
tion and  the  excess  of  acid  determined  by  titration.  o.i  of  the  number 
of  c.c.  of  acid  neutralised  gives  the  provisional  malic-acid  value  which 
should  not  be  below  0.80  with  pure  maple  products. 

Horvet  (/.  Amer.  Chew.Soc.,  1904,  26,  1523)  measures  the  volume 
of  the  lead  precipitate  after  concentration  by  a  centrifuge.  Adulter- 
ated articles  give  much  less  precipitate. 

Winton  and  Kreider  (/.  Amer.  Chem.  Soc.,  1906,  28,  1204),  in- 
stead of  measuring  the  volume  of  the  precipitate  produced  by  adding 
basic  lead  acetate  to  maple  products,  determine  the  amount  of  lead  in 
this  precipitate.  The  lead  numbers  vary  from  1.2  to  1.77  for  genuine 
syrups  and  1.8  to  2.5  for  sugars. 


39°  SUGARS. 

The  following  tests,  due  to  Sy  (/.  Amer.  Chem.Soc.,  1908,  30,  1429- 
1431,  1611-1616),  are  stated  to  be  of  considerable  value. 

Colour  Test. — 15  c.c.  of  syrup  or  15  grm.  of  sugar  and  enough 
water  to  make  15  c.c.  are  very  thoroughly  mixed  in  a  test-tube  with 
3  c.c.  of  pure  amyl  alcohol  and  i  c.c.  of  a  20%  solution  of  phosphoric 
acid  and  allowed  to  stand  until  the  alcohol  separates.  The  alcoholic 
layer  shows  a  decided  brown  colour  with  pure  maple  products;  with 
adulterated  samples  the  colour  varies  from  a  very  pale  to  a  light  brown, 
according  to  the  proportion  of  maple  product;  cane  products  containing 
caramel  give  no  colour. 

Foam  Test. — 5  c.c.  of  syrup  are  treated  in  a  narrow  tube  graduated 
to  o.i  c.c.  with  10  c.c.  of  water,  the  mixture  is  thoroughly  shaken  for 
half  a  minute  and  allowed  to  stand  for  10  minutes,  when  the  volume 
of  foam  is  read.  With  pure  maple  products  the  amount  is  never 
less  than  3  c.c.;  adulterated  products  all  give  less. 

Volume  of  Basic  Lead  Acetate  Precipitate. — 5  c.c.  of  syrup  or  5 
grm.  of  sugar  and  water  to  make  5  c.c.  are  placed  in  a  glass-stoppered 
25  c.c.  measuring  cylinder  with  10  c.c.  of  water  and  2  c.c.  of  10%  basic 
lead  acetate  solution.  The  whole  is  thoroughly  mixed  and  allowed 
to  settle  for  20  hours  when  the  volume  of  the  precipitate  is  read.  For 
pure  maple  products  this  will  be  over  3  c.c.  and  is  usually  over  5  c.c.; 
with  adulterated  products  the  volume  is  less. 

A  valuable  criterion  of  the  purity  of  a  maple  product  is  the  lead 
value  defined  as  the  amount  of  lead  precipitated  on  adding  lead  acetate 
solution  to  100  c.c.  of  syrup  or  100  grm.  of  sugar.  50  c.c.  of  syrup 
or  50  grm.  of  sugar  are  heated  to  boiling  with  200  c.c.  water  to  expel 
any  fermentation  products,  20  c.c.  of  10%  normal  lead  acetate  added 
and  again  boiled.  The  solution  is  filtered  when  cold  and  the  precipi- 
tate washed  with  water  at  20°.  The  filter  and  precipitate  are  treated 
with  15  c.c.  of  concentrated  nitric  acid  and  10  c.c.  of  concentrated 
hydrochloric  acid,  heated  to  disintegrate  the  filter,  cooled,  10  c.c. 
concentrated  sulphuric  acid  added,  and  the  whole  heated  to  expel 
all  nitric  acid.  If  the  blackening  does  not  disappear,  5  c.c.  more 
nitric  acid  are  carefully  added  after  cooling  and  the  whole  is  again 
heated  to  expel  all  nitric  acid.  The  cooled  solution  is  diluted  with 
50  c.c.  water,  cooled  and  100  c.c.  alcohol  added.  After  6  hours,  the 
lead  sulphate  is  filtered  on  an  asbestos-packed  gooch,  washed  with 
alcohol  and  ignited  at  a  low  red  heat  and  weighed.  The  weight 
multiplied  by  1.366  (2  x  0.683)  gives  the  lead  value  which  should 


GLUCOSIDES.  391 

not  be  less  than  0.25  and  is  usually  over  0.30.  It  will  be  noted  that 
this  method  differs  from  analagous  methods  now  in  use  by  the  substi- 
tution of  normal  lead  acetate  for  the  basic  salt. 


GLUCOSIDES. 

The  name  glucoside  is  applied  to  a  numerous  class  of  substances 
occurring  in  plants  and  seeds  which  yield  a  glucose,  C6H12O6,  generally 
dextrose,  on  hydrolysis  with  acids.  The  other  constituents  yielded 
by  glucosides  are  numerous,  comprising  alcohols,  phenols,  most  of 
the  vegetable  dye-stuffs,  mustard  oil,  many  poisons,  etc.  A  class  of 
glucosides  of  some  industrial  importance  since  they  are  poisonous  and 
yield  hydrogen  cyanide  on  hydrolysis  are  known  as  cyanogenetic  glu- 
cosides. They  have  been  found  in  many  fodder  plants.  Most  of  the 
glucosides  are  accompanied  in  the  plant  by  an  enzyme  capable  of  hy- 
drolysing  them.  Enzyme  and  glucoside  are  stored  in  different  cells  in 
the  plant,  but  act  on  one  another  when  the  plant  is  macerated  with 
water.  To  extract  a  glucoside,  therefore,  it  is  first  necessary  to  de- 
stroy the  enzyme;  this  is  often  effected  by  boiling  the  plant  with  alcohol. 
Whilst  the  action  of  the  enzyme  is  very  specific  and  limited,  as  a  rule,  to 
a  few  closely  related  compounds,  very  many  of  the  glucosides  which 
are  /^-dextrose  derivatives  are  hydrolysed  by  emulsin,  an  enzyme  very 
widely  distributed  in  plants  and  conveniently  prepared  from  almonds. 

The  detection  and  determination  of  a  glucoside  in  plant  products  is 
often  best  performed  on  the  non-sugar  constituent.  Provided  cane 
sugar  or  other  disaccharides  are  not  present,  the  change  in  cupric 
reducing  power  on  hydrolysis  by  acids  may  be  made  use  of.  It  is 
often  preferable  to  extract  the  glucosides  by  means  of  solvents  and 
weigh  as  such. 

Bourquelot  (Arch.  Phann.,  1907,  245,  172)  has  elaborated  a  method 
for  their  detection  by  means  of  emulsin  which  he  prepares  by  crushing 
blanched  almonds  in  a  mortar  and  macerating  each  100  grm.  with  200 
c.c.  of  distilled  water  containing  chloroform  for  24  hours  at  the  normal 
temperature.  The  mixture  is  strained,  pressed,  protein  precipitated  by 
10  drops  of  glacial  acetic  acid  and,  after  filtering,  the  enzyme  pre- 
cipitated by  95%  alcohol.  The  enzyme  is  collected,  washed  with  a 
mixture  of  equal  volumes  of  ether  and  alcohol  and  dried  in  vacua.  It 
is  obtained  as  a  white  powder. 

To    detect    glucosides,    the    material    is    first    boiled    with   95% 


392  SUGARS. 

alcohol,  any  acidity  neutralised  with  calcium  carbonate,  the  spirit 
is  distilled  off  and  the  residue  made  up  to  250  c.c.  with  water  containing 
a  little  thymol.  Since  the  emulsin  sometimes  contains  invertase, 
the  material  is  first  treated  with  invertase  to  eliminate  sucrose,  as 
described  on  page  314,  heated  to  boiling  for  a  few  minutes  to  destroy 
the  invertase  and  then  treated  with  the  emulsin  preparation.  The 
optical  rotation  is  ascertained  before  and  after  hydrolysis;  a  change, 
if  observed,  denotes  the  presence  of  a  /3-glucoside  of  dextrose. 

The  problem  often  presents  itself  which  of  the  glucose  sugars 
is  present  in  a  glucoside.  Ter  Meulen  (Rec.  Trav.  Chim.,  1905,  24, 
444)  applies  the  principle,  independently  discovered  by  E.  F.  Arm- 
strong (Proc.  Roy.  Soc.,  1904,  73,  516),  that  the  rate  of  action  of  a  par- 
ticular enzyme  is  hindered  only  by  that  sugar  the  glucosidic  deriva- 
tive of  which  is  hydrolysed  by  the  enzyme. 

By  measuring  the  rate  of  hydrolysis  of  the  glucoside  by  its  enzyme  in 
the  presence  of  various  other  sugars  one  only  is  found  to  retard,  and 
this  is  the  sugar  present  in  the  glucoside. 

To  ascertain  whether  a  glucoside  is  a  derivative  of  a-  or  /3-dex- 
trose,  E.  F.  Armstrong  hydrolyses  with  an  active  enzyme  for  half 
an  hour  and  determines  the  change  in  optical  rotatory  power  produced 
by  the  addition  of  a  drop  of  aqueous  ammonia.  A  decrease  de- 
notes the  presence  of  a-dextrose,  an  increase  that  of  /^-dextrose. 
Dunstan,  Henry  and  Auld  (Proc.  Roy.  Soc.,  1907,  6-79,  315,  322)  have 
applied  this  method  with  success  to  the  identification  of  a-dextrose  in 
phaseolunatin. 

Cyanogenetic  glucosides  are  best  determined  by  means  of  the  hydro- 
gen cyanide  they  produce  when  hydrolysed,  as  it  is  the  poisonous  nature 
of  the  feeding  stuffs  in  which  they  occur  which  is  really  in  question. 
Henry  and  Auld  (/.  Soc.  Chem.  Ind.,  1908,  27,  428)  have  quite 
recently  described  the  following  method  of  procedure  which  gives  the 
maximum  amount  of  hydrocyanic  acid  obtainable.  The  product  is 
ground  as  rapidly  as  possible,  weighed,  placed  in  a  Soxhlet  extraction 
apparatus  and  repercolated  with  hot  alcohol  so  as  to  dissolve  out  the 
glucoside.  The  solvent  is  distilled  off  and  the  residue  mixed  with 
50  c.c.  of  water  and  10  c.c.  of  10%  hydrochloric  or  sulphuric 
acid  added.  The  mixture  is  then  distilled  preferably  in  a  current  of 
steam  until  hydrocyanic  acid  can  no  longer  be  found  in  the  distillate 
in  which  it  may  be  estimated  volumetrically  by  Liebig's  method.  The 
authors  prefer  to  add  a  slight  excess  of  sodium  hydrogen  carbonate  and 


URINE   ANALYSIS.  393 

titrate  with  an  excess  of  iodine  solution.  A  little  of  the  freshly 
ground  product  is  macerated  with  water  in  presence  of  an  antiseptic  to 
ascertain  whether  hydrogen  cyanide  is  formed,  thereby  denoting  the 
presence  of  the  enzyme. 

URINE  ANALYSIS. 

Sugars  in  urine  may  be  detected  and  estimated  either  polari- 
metrically  or  by  means  of  their  reducing  power  or  by  the  other  usual 
methods  elsewhere  described.  Normal  urine  at  the  most  contains 
only  traces  of  dextrose,  but  on  the  other  hand,  traces  of  substances  other 
than  glucoses,  such  as  creatinine  and  uric  acid,  also  glucuronic  acid  are 
normally  present,  all  of  which  reduce  Fehling's  solution.  Moreover, 
other  optically  active  substances  are  generally  present,  so  that  urine 
requires  a  preliminary  treatment  before  applying  the  sugar  tests  and  it 
is  necessary  to  make  confirmatory  tests  to  be  sure  sugar  is  present.  Too 
great  a  stress  must  not  be  laid  on  the  presence  of  an  insignificant  pro- 
portion of  sugar.  It  is  desirable  before  applying  the  sugar  tests  to 
remove  proteins,  if  present,  by  adding  a  few  drops  of  acetic  acid,  heat- 
ing to  boiling  and  filtering  from  any  precipitate  formed. 

The  liquid  should  then  be  rendered  distinctly  alkaline  by  sodium 
hydroxide,  filtered  from  any  precipitate,  and  the  copper  solution 
employed  in  the  following  manner: 

Heat  to  boiling  in  a  test-tube  10  c.c.  of  Fehling's  solution,  prepared 
in  the  usual  way,  previously  introducing  a  few  small  fragments  of  clay 
tobacco-pipe  to  prevent  bumping.  When  boiling,  add  0.5  to  i  c.c 
of  the  urine,  previously  treated  as  indicated  above.  If  sugar  is  abund- 
ant, a  yellowish  or  brick-red  opacity  and  deposit  will  be  produced.  If 
a  negative  reaction  is  obtained,  test  for  traces  of  sugar  by  adding 
7  c.c.  or  8  c.c.  of  the  urine  to  the  hot  liquid,  heating  again  to  ebulli- 
tion, and  then  setting  the  tube  aside  for  some  time.  If  no  turbidity  is 
produced  as  the  mixture  cools,  the  urine  is  either  quite  free  from 
sugar  or  at  any  rate  contains  less  than  0.025%.  If  tne  quantity  of 
sugar  present  is  small — that  is,  under  0.5% — the  precipitation  of  the 
yellow  or  red  cuprous  oxide  does  not  take  place  immediately,  but 
occurs  as  the  liquid  cools,  the  appearance  being  somewhat  peculiar. 
The  liquid  first  loses  its  transparency,  and  passes  from  a  clear  bluish- 
green  to  an  opaque,  light-greenish  colour.  This  green  milky  appear- 
ance is  quite  characteristic  of  dextrose. 


394  SUGARS. 

The  colours  of  the  precipitates  obtained  are  attributed  by  some 
authors  to  the  proportion  of  alkali  present,  the  yellow  and  green  pre- 
cipitates being  forms  of  cuprous  hydrate.  In  other  cases  the  disturb- 
ance is  said  to  be  due  to  the  presence  of  .creatinine.  On  adding  Feh- 
ling's solution  to  a  solution  of  this  substance,  a  green  liquid  is  produced, 
and  on  boiling  a  yellow  colouration  is  observed,  without,  however,  any 
separation  of  cuprous  oxide.  It  is  this  behaviour  which  causes  inter- 
ference with  the  detection  of  glucoses,  the  combination  of  the  yellow 
and  blue  colours  resulting  in  a  green,  and  in  addition  the  creatinine 
compound  is  said  to  have  the  power  of  preventing  the  precipitation  of 
cuprous  oxide  by  glucoses. 

Nylander's  test  which  is  not  affected  by  creatinine  or  uric  acid  con- 
sists in  boiling  the  urine  for  2  to  5  minutes  with  a  small  quantity  of  a 
solution  containing  100  grm.  of  sodium  hydroxide  (sp.  gr.  1.12),  4  grm. 
of  potassium  sodium  tartrate  and  2  grm.  of  bismuth  subnitrate,  when 
a  black  precipitate  forms  on  cooling. 

The  detection  and  estimation  of  sugars  in  urine  offers,  but  little 
difficulty  when  the  amount  is  0.25%  or  over,  but  when  the  quantity 
is  very  small  satisfactory  results  are  not  often  attainable.  The  oc- 
curence  of  sugar  normally  in  the  urine  has  been  much  disputed.  By 
the  use  of  phenylhydrazine — a  method  free  from  the  objections  and  fal- 
lacies which  underlie  nearly  all  other  tests — it  seems  proved  that,  while 
normal  human  urine  may  sometimes  contain  traces  of  sugar,  that  sub- 
stance is  by  no  means  constantly  present,  and  a  great  number  of  the 
recorded  observations  are  quite  inconclusive. 

It  is  important  to  consider  the  extent  to  which  these  bodies  interfere, 
and  the  manner  in  which  they  may  be  removed  or  their  influence 
obviated.  The  chief  of  these  are  uric  acid,  xanthine,  and  creatinine,  but 
under  some  conditions  urine  contains  glucuronic  acid  or  compounds 
thereof  which  simulate  sugar  very  closely.  The  amount  of  uric  acid 
passed  per  diem  under  ordinary  conditions  is  said  to  be  about  0.5  grm., 
though,  of  course,  in  many  instances  it  is  considerably  more.  Xan- 
thine and  the  allied  bodies  are  present  in  still  smaller  amount.  Accord- 
ing to  Voit,  the  proportion  of  creatinine  passed  in  24  hours  ranges 
from  0.5  to  nearly  5  grm.  Urine  containing  the  latter  amount  would 
exert  a  reducing  action  on  Fehling's  or  Pavy's  solution  equivalent  to 
the  presence  of  0.32%  of  glucose. 

Dextrose  in  urine  may  be  estimated  by: 

i.  Titration  with  Fehling's  solution  in  the  usual  manner. 


URINE    ANALYSIS.  395 

2.  Titration  with  Pavy's  solution. 

3.  Titration  with  Knapp's  mercurial  solution. 

4.  Polarisation. 

5.  Fermentation. 

For  ordinary  clinical  purposes  very  great  accuracy  is  not  required. 
In  such  cases  as  the  proof  of  a  diminution  in  the  amount  of  sugar  fol- 
lowing treatment,  the  errors  of  collecting  urine  properly  and  multiplica- 
tion so  as  to  give  the  daily  output,  more  than  counterbalance  slight 
errors  in  the  estimation. 

Before  polarising,  the  urine  may  be  clarified  and  freed  from  proteins, 
uric  acid,  phosphates  and  colouring  matters  by  precipitating  with 
alumina  cream  or  with  basic  lead  acetate.  Thus,  100  c.c.  of  urine  of 
known  sp.  gr.  are  measured  into  a  flask,  5  c.c.  of  the  clarifying  re- 
agent added,  the  solution  made  up  to  no  c.c.,  shaken,  filtered  and 
polarised.  To  make  certain  that  the  rotation  obtained  is  really  due 
to  dextrose,  the  urine  is  examined  polarimetrically  before  and  after 
fermentation,  the  change  in  rotatory  power  indicating  the  amount  of 
dextrose  present. 

The  fermentation  test  for  dextrose  in  urine  is  very  useful  for  con- 
firmatory purposes  and  also  serves  to  distinguish  between  dextrose 
and  unfermentable  pentoses,  lactose  or  glucuronic  acid.  Fermenta- 
tion at  34  to  36°  should  be  complete  in  6  hours.  If  the  operation  be 
prolonged  the  gas  formed  is  probably  due  to  other  changes.  The 
Lohnstein  saccharometer  is  often  used  in  physiological  laboratories  for 
this  purpose. 

Fehling's  solution  is  used  either  gravimetrically  or  volumetrically  in 
the  ordinary  manner. 

Modified  Fehling  Solution. — For  examination  of  urine  the  following 
modification  of  the  copper  solution  is  strongly  recommended  by  S.  R. 
Benedict  (/.  Biol.  Chem.,  1909,  5,  485): 

Copper  sulphate  (cryst),  8.65  grm. 
Sodium  citrate,  86.50  grm. 

Sodium  carbonate  (dry) ,  50.00  grm. 

The  sodium  citrate  and  carbonate  are  dissolved  in  300  c.c.  of  water, 
filtered  if  necessary,  and  made  up  to  425  c.c.  The  copper  sulphate 
is  dissolved  in  50  c.c.  of  water  and  made  up  to  75  c.c.  The  solutions 
are  mixed.  The  mixture  keeps  well.  Benedict  found  that  commer- 


396  SUGARS. 

cial  sodium  citrate  is  satisfactory.  The  solution  is  not  reduced  by 
uric  acid,  chloroform,  chloral,  or  formaldehyde. 

Pavy's  solution  may  also  be  used  for  the  determination  of  the  glu- 
cose in  diabetic  urine,  though  it  cannot  be  employed  for  the  detection 
of  small  quantities  of  the  sugar.  Muller  and  Hagen  determine  the 
sugar  volumetrically  by  Knapp's  mercurial  solution,  which  has  the 
advantage  of  being  applicable  to  samples  of  urine  containing  as 
little  as  0.1%  of  glucoses,  while  Fehling's  solution  cannot  be  applied 
quantitatively  in  the  ordinary  manner  if  less  than  0.5%  of  dex- 
trose be  present,  owing  to  the  incomplete  separation  of  the  cuprous 
oxide  in  presence  of  certain  obscure  foreign  matters  contained  in 
urine.1 

To  render  urine  fit  for  the  application  of  Fehling's  solution,  Carne- 
lutti  and  Valente  recommend  that  100  c.c.  of  the  sample  should  be 
evaporated  to  a  syrup  on  the  water-bath,  i  c.c.  of  a  25%  solution  of 
zinc  chloride  previously  mixed  with  1/4  of  its  volume  of  hydrochloric 
acid  is  added,  then  2  volumes  of  absolute  alcohol,  and  the  whole  allowed 
to  stand  for  some  hours.  The  liquid  is  then  filtered,  the  residue  washed 
with  alcohol,  the  alcohol  evaporated  from  the  solution,  and  the  residual 
liquid  made  up  to  100  c.c.  with  distilled  water.  In  this  solution  excel- 
lent results  are  said  to  be  obtainable  by  Fehling's  solution. 

Copper  sulphate  yields  at  first  little  or  no  precipitate  with  normal 
urine  in  the  cold,  but  on  standing  or  boiling  a  pale  green  precipitate 
is  thrown  down  which  has  a  tendency  to  darken  if  the  heating  be  con- 
tinued. If  copper  acetate  be  used,  or  sodium  acetate  with  copper  sul- 
phate, the  precipitation  is  more  complete,  uric  acid,  xanthine,  hypoxan- 
thine,  colouring  matter,  and  albumin  being  entirely  thrown  down,  and 
creatinine  and  phosphates  partially.  The  filtered  liquid  cannot  be  used 
for  the  phenylhydrazine  test,  and  the  presence  of  copper  unfits  it  for 
titration  by  Pavy's  solution;  but  it  is  admirably  suited  for  the  detection 
of  small  quantities  of  sugar  by  Fehling's  test,  as  follows: 

From  7  to  8  c.c.  of  the  sample  are  heated  to  boiling,  and,  without 
separating  any  precipitate  of  proteins,  5  c.c.  of  the  solution  of  copper 
sulphate  used  for  preparing  Fehling's  test  are  added  and  the  liquid 
again  boiled.  This  produces  a  precipitate  principally  uric  acid,  xan- 
thine, hypoxanthine,  and  phosphates.  To  render  the  precipitation  com- 

1J.  G.  Otto  recommends  that,  for  titrating  solutions  containing  i  to  0.5%  sugar,  the 
Knanp's  solution  should  be  diluted  with  4  volumes  of  water,  for  those  containing  0.5  to 
0.1%.  with  3  volumes  of  water,  while  for  solutions  containing  less  than  0.1%  2  volumes 
of  water  should  be  added.  In  all  cases  the  urine  should  be  added  gradually  to  the  mercurial 
solution. 


URINE    ANALYSIS.  397 

plete,  however,  it  is  desirable  to  add  to  the  liquid,  when  partially  cooled, 
from  i  to  2  c.c.  of  a  saturated  solution  of  sodium  acetate  having  a  feebly 
acid  reaction.  The  liquid  is  filtered,  and  to  the  filtrate,  which  will  have 
a  bluish-green  colour,  5  c.c.  of  the  alkaline  tartrate  mixture  used  for 
for  fifteen  to  twenty  seconds.  In  the  presence  of  more  than  0.25% 
preparing  Fehling's  solution  are  next  added,  and  the  liquid  boiled 
of  sugar,  separation  of  cuprous  oxide  occurs  before  the  boiling  point 
is  reached,  but  with  smaller  proportions  precipitation  takes  place 
during  the  cooling  of  the  solution,  which  becomes  greenish,  opaque, 
and  suddenly  deposits  cuprous  oxide  as  a  fine  orange-yellow  precipi- 
tate. When  a  urine  rich  in  sugar  is  under  examination,  the  volume 
taken  can  be  advantageously  reduced  from  7  or  8  c.c.  to  2  or  3  c.c.  or 
even  less,  water  being  added  to  replace  it. 

It  is  evident  that  in  this  modification  of  the  ordinary  Fehling's  test 
advantage  is  taken  of  the  very  general  precipitating  power  of  cupric 
acetate  to  remove  from  the  urine  the  great  majority  of  those  sub- 
stances which  interfere  with  the  detection  of  sugar,  by  themselves 
reducing  the  alkaline  copper  solution,  retaining  the  cuprous  oxide 
in  solution,  or  producing  a  flocculent  precipitate  which  masks  the 
true  reaction  of  sugar.  Operating  as  described  above,  no  greenish 
turbidity  refusing  to  settle  is  produced,  and  hence  the  separation  of  any 
cuprous  oxide  is  very  readily  observed.  It  is  important  that  the  sodium 
acetate  should  not  be  added  till  the  liquid  has  partially  cooled,  so  as 
to  avoid  any  chance  of  reaction  of  the  resultant  cupric  acetate  with  the 
glucose  in  the  manner  observed  by  Barfoed. 

Pavy's  method  of  estimating  sugar  by  titration  with  ammoniacal 
cupric  solution  would  probably  be  more  generally  applied  if  it  did  not 
necessitate  the  use  of  a  special  apparatus.  The  following  form  of 
thre  test  is  simple  and  covenient,  but  less  accurate  than  where  larger 
quantities  of  the  urine  and  reagent  are  employed.  An  accurately 
measured  volume  of  10  c.c.  of  Pavy's  solution  is  placed  in  a  wide  test- 
tube,  a  few  fragments  of  tobacco-pipe  dropped  in,  and  8  to  10  drops  of 
petroleum  or  paraffin  burning  oil  added.  This  forms  an  upper  layer 
which  effectually  excludes  the  air.  The  test-tube  is  inserted  into  the 
neck  of  a  wide-mouthed  flask  containing  hot  water,  which  is  then 
heated  until  the  contents  of  the  tube  have  reached  the  point  of  ebullition. 
The  urine  to  be  tested  is  treated  with  an  equal  volume  of  ammonia 
and  filtered  from  the  precipitated  phosphates.  A  known  volume  of 
the  filtrate  is  then  further  diluted  with  a  definite  quantity  of  water, 


SUGARS. 

according  to  the  proportion  of  sugar  supposed  to  be  present,  and  then 
added  drop  by  drop  to  the  boiling-hot  Pavy's  solution  by  means  of 
a  small  burette  or  graduated  pipette,  until  the  disappearance  of  the 
blue  colour  indicates  the  termination  of  the  reaction.  If  10  c.c/  of 
Pavy's  solution  were  employed,  the  volume  of  urine  required  to  de- 
colourise it  contains  0.005  grm.  of  sugar. 

Unclarified  healthy  human  urine  may  exert  a  reducing  action  on 
Pavy's,  solution  equal  to  that  of  a  liquid  containing  from  o.i  to  0.3% 
of  dextrose.  Of  this,  one-quarter  is  ascribed  to  uric  acid  (removable 
by  lead  acetate)  and  the  remainder  to  creatinine  (removable  by  mer- 
curic chloride). 

The  phenylhydrazine  test  for  dextrose  has  a  special  value  as  it  is  not 
given  by  the  other  non-sugar  reducing  substances  in  the  urine.  To 
apply  it,  50  c.c.  of  the  suspected  urine  previously  freed  from  protein, 
are  heated  in  the  boiling  water-bath  for  an  hour,  with  10  to  20  drops  of 
phenylhydrazine  and  the  same  volume  of  50%  acetic  acid.  5  grm.  of 
sodium  chloride  may  be  added  to  facilitate  precipitation.  If  any 
quantity  of  dextrose  is  present,  an  orange-yellow,  generally  crystalline, 
precipitate  separates  in  the  hot  liquid  or  on  cooling.  This  should  be 
filtered  when  cold,  well  washed  with  water  to  remove  excess  of  phenyl- 
hydrazine and  crystallised  from  a  small  quantity  of  dilute  alcohol  when 
characteristic  yellow  needles  are  obtained,  melting  at  205°  and  prac- 
tically insoluble  in  boiling  water. 

When  only  minute  traces  of  sugar  are  present,  the  complete  separa- 
tion of  the  glucosazone  requires  some  time,  but  the  qualitative  indica- 
tion is  readily  and  quickly  obtained.  Dextrose  and  laevulose  yield  the 
same  glucosazone,  the  pentoses  and  glucuronic  acid  (see  later)  also 
yield  insoluble  compounds  with  phenylhydrazine. 

Is  is  important  that  the  phenylhydrazine  used  should  be  of  good 
quality.  It  should  be  almost  straw-yellow  in  colour  and  is  conveniently 
kept  in  sealed  bottles  containing  only  a  small  quantity  which  can  be 
quickly  used  when  once  opened. 

Salkowski  takes  5  c.c.  of  urine,  0.5  c.c.  of  glacial  acetic  acid  and  20 
drops  of  phenylhydrazine,  boils  for  i  minute,  adds  5  drops  of  15% 
sodium  hydroxide,  and  a  volume  of  water  equal  to  3/4  of  the  original 
volume  and  heats  nearly  to  boiling.  After  standing  24  hours,  a 
sulphur-yellow  precipitate  of  slender  needles  is  obtained  if  dextrose 
were  present,  but  not  from  lactose  or  maltose. 

Unfortunately,  the  phenylhydrazine  test  cannot  be  applied  quanti- 


IRINE    ANALYSIS.  399 

tatively  though  the  amount  of  precipitate  formed  gives  a  fair  indication 
of  the  proportion  of  sugar  present. 

Glucuronic  Acid. — As  already  stated  glucuronic  acid  simulates 
the  behaviour  of  dextrose  very  closely  and  gives  not  only  all  the  ordinary 
reactions  as  a  reducing  agent,  but  is  the  only  other  constituent  of  urine 
which  reacts  with  phenylhydrazine. 

Glucuronic  acid  is  a  syrupy  liquid,  miscible  with  alcohol  or  water. 
When  the  aqueous  solution  is  boiled,  evaporated,  or  even  allowed  to 
stand  at  the  ordinary  temperature,  the  acid  loses  the  elements  of  water 
and  yield  the  anhydride  or  lactone  (CeHsOe),  which  forms  monoclinic 
tables  or  needles,  having  a  sweet  taste  and  melting  at  167°.  The 
lactone  is  insoluble  in  alcohol,  but  dissolved  by  water  to  form  a  solu- 
tion which  is  dextrorotatory  ( [a]D=  19.25°),  prevents  the  precipitation 
of  cupric  solutions  by  alkalies,  and  powerfully  reduces  hot  Fehling's 
solution,  the  cupric  reducing  power  being  98.8  compared  with  dextrose 
as  100.  The  acid  is  dextrorotatory  (  [0]D=35°),  but  many  of  its 
compounds  are  laevorotatory.  It  reduces  Fehling's  solution  on  heating, 
and  precipitates  the  metals  from  hot  alkaline  solutions  of  silver,  mer- 
cury, and  bismuth.  With  phenylhydrazine,  glucuronic  acid  forms  a 
yellow  crystalline  compound,  melting  at  114  to  115°,  and  resembling 
closely  phenylglucosazone.  When  oxidised  with  bromine  glucuronic 
acid  yields  saccharic  acid,  which  can  be  again  reduced  to  glucuronic 
acid  by  treatment  with  sodium  amalgam.  It  is  distinguished  from 
glucose  by  not  undergoing  the  alcoholic  fermentation  when  treated 
with  yeast. 

It  gives  the  orcinol  and  phloroglucinol  reactions  for  pentoses  as  it 
is  dehydrated  on  boiling  with  hydrochloric  acid,  yielding  furfural 
and  carbon  dioxide,  but  the  production  of  furfural  is  much  slower 
than  in  the  case  of  the  pentoses.  The  carbon  dioxide  evolved 
may  be  used  to  estimate  glucuronic  acid.  To  effect  this,  Lefevre  and 
Tollens  (Ber.,  1907,  40,  4513)  boil  with  hydrochloric  acid  (sp.  gr 
i. 06)  for  31/2  hours  and  aspirate  a  current  of  pure  air  through  the 
apparatus;  the  carbon  dioxide  is  washed  and  absorbed  in  potash  bulbs 
and  weighed.  The  results  are,  as  a  rule,  too  high  owing  to  the 
presence  of  other  substances  which  yield  carbon  dioxide. 

Combined  with  the  determination  of  the  furfural,  this  method 
affords  a  simultaneous  estimation  of  pentoses  and  glucuronic  anhy- 
dride. Three  parts  of  glucuronic  anhydride  give  one  part  of  furfural 
phloroglucide. 


400  SUGARS. 

Tollens  (Ber.,  1908,  41,  1788-1790)  finds  that  glucuronic  acid 
alone  and  not  the  pentoses  form  a  blue  substance  on  heating  with 
naphthoresorcinol  and  hydrochloric  acid  which  is  soluble  in  ether. 
This  enables  glucuronic  acid  to  be  identified  with  certainty  in  presence 
of  pentoses. 

Other  Sugars  in  Urine. — Recent  researches  have  shown  the  occa- 
sional presence  of  other  sugars  besides  dextrose  in  pathological  urine. 
The  reducing  action  of  a  urine  may  indicate  dextrose,  laevulose,  lactose, 
pentoses  or  glucuronic  acid,  the  fermentation  test  only  dextrose  and 
laevulose. 

These  sugars  are  best  detected  by  means  of  the  substituted  phenyl- 
hydrazines. 

To  detect  pentoses  in  urine,  the  orcinol  test  is  carried  out  as  follows. 
0.03  grm.  of  powdered  orcinol  are  dissolved  in  10  c.c.  of  fuming  hydro- 
chloric acid  and  a  drop  of  dilute  ferric  chloride  added.  5  c.c.  of  this 
solution  and  2  c.c.  of  urine  are  placed  in  a  tube  closed  with  a  plug  of 
cotton  wool  and  heated  nearly  to  boiling.  If  pentoses  are  present  an 
emerald-green  colouration  gradually  appears,  which  soon  becomes 
dark  green. 

To  estimate  pentoses  in  urine,  Jolles  (Zeit.  anal.  Chem.,  1907,46, 
764)  proceeds  as  follows:  The  urine  is  boiled  with  a  few  drops  of 
acetic  acid  and  concentrated,  if  necessary,  to  free  it  from  interfering 
volatile  substances.  100  c.c.  are  distilled  with  150  c.c.  hydrochloric 
acid  (sp.  gr.  1.06)  in  a  current  of  steam  until  the  distillate  amounts 
to  1000  c.c.  100  c.c.  of  this  are  neutralised  with  an  excess  of  20% 
sodium  hydroxide,  using  methyl-orange  as  indicator;  half-normal 
hydrochloric  acid  is  added  to  restore  the  red  colouration  and  the 
liquid  titrated  with  sodium  hydrogen  sulphite  and  standard  iodine 
solution. 

For  further  information  consult  "Analyse  des  Harns" 

PENTOSES. 

The  best  known  pentoses  are  arabinose  and  xylose.  Even  more 
important  are  their  polymerides — the  pentosans. 

Arabinose  and  xylose,  in  the  absence  of  other  sugars,  may  be  detected 
and  estimated  in  the  same  manner  as  dextrose — either  polarimetric- 
ally  or  by  means  of  copper  or  mercuric  solutions. 

Characteristic  are  the  colourations  produced  with  alcoholic  solutions 
of  phenols  and  hydrochloric  or  sulphuric  acid  on  cautious  heating. 


PENTOSES.  401 

Orcinol  gives  a  bluish-violet  colouration  in  the  cold,  and  on  warming, 
a  reddish,  changing  to  violet-blue  and  finally  bluish-green  flakes  sepa- 
rate which  dissolve  in  alcohol,  showing  a  characteristic  absorption- 
spectrum.  The  orcinol  reagent  is  prepared  by  dissolving  i  grm.  of 
orcinol  in  200  c.c.  of  94%  alcohol.  3  drops  are  added  to  5  c.c.  of 
the  sugar  solution  and  then  5  c.c.  of  concentrated  hydrochloric  acid. 
The  mixture  is  shaken  and  heated  on  a  boiling  water  bath  for  half  an 
hour.  The  method  is  not  available  in  presence  of  laeonlose  when  a 
bronze  brown  colouration  is  obtained  (Pieraerts.  Bull.  Assoc.  Chim. 
Sucr.  et  Dist.,  1908,  26,  46). 

Phloroglucinol  and  hydrochloric  acid  cause  a  bright  cherry-red 
on  heating  and  the  solution  so  prepared  has  a  very  characteristic 
spectrum. 

A  more  general  method,  which  is  applicable  also  to  the  pentosans, 
consists  in  distillation  with  hydrochloric  acid  in  a  current  of  steam 
whereby  furfural  is  formed  and  estimated  by  means  of  its  compounds 
with  phloroglucinol,  phenylhydrazine  or  sodium  hydrogen  sulphite. 

Of  these  the  phenylhydrazine  method  is  least  satisfactory.  When 
using  sodium  hydrogen  sulphite,  an  aliquot  portion  of  the  distillate  is 
mixed  with  a  known  volume  in  excess  of  the  standard  hydrogen  sul- 
phite. After  two  hours'  standing,  this  excess  is  estimated  by  titration 
with  standard  iodine  solution:  i  c.c.  of  normal  sodium  hydrogen 
sulphite  solution  is  equivalent  to  0.07505  grm.  of  pentose. 

The  phloroglucinol  method  has  been  worked  out  in  great  detail  by 
Krober  (/.  Land.,  1900,  48,  379)  and  adopted  by  the  A.  O.  A.  C. 
The  details  are  as  follows: 

Qualitative  Test  of  the  Purity  of  the  Phloroglucinol.  —Dis- 
solve a  small  quantity  of  the  phloroglucinol  in  a  few  drops  of  acetic 
anhydrid,  heat  almost  to  boiling,  and  add  a  few  drops  of  concentrated 
sulphuric  acid.  A  violet  colour  indicates  the  presence  of  diresorcinol. 
A  phloroglucinol  which  gives  more  than  a  faint  colouration  may  be 
purified  by  the  following  method:  Heat  in  a  beaker  about  300  c.c. 
of  hydrochloric  acid  ( sp.  gr.  1.06)  and  n  grm.  of  commercial  phloroglu- 
cinol, added  in  small  quantities  at  a  time,  stirring  constantly  until  it  has 
almost  entirely  dissolved.  Some  impurities  may  resist  solution,  but  it 
is  unnecessary  to  dissolve  them.  Pour  the  hot  solution  into  a  sufficient 
quantity  of  the  same  hydrochloric  acid  (cold)  to  make  the  volume  1500 
c.c.  Allow  it  to  stand  at  least  overnight — better  several  days — to  allow 
the  diresorcinol  to  crystallise  out,  and  filter  immediately  before  using. 
VOL.  1—26 


4O2  SUGARS. 

The  solution  may  turn  yellow,  but  this  does  not  interfere  with  its 
usefulness.  In  using  it,  add  the  volume  containing  the  required 
amount  to  the  distillate. 

Procedure.  —  Place  a  quantity  of  the  material,  chosen  so  that  the 
weight  of  phloroglucide  obtained  shall  not  exceed  0.300  grm.  in  a 
flask,  together  with  100  c.c.  of  12%  hydrochloric  acid  (sp.  gr.  1.06), 
and  several  pieces  of  recently  heated  pumice  stone.  Place  the  flask 
on  a  wire  gauze,  connect  with  a  condenser,  and  heat,  rather  gently 
at  first,  and  so  regulate  as  to  distill  over  30  c.c.  in  about  ten  minutes,  the 
distillate  passing  through  a  small  filter-paper.  Replace  the  30  c.c 
driven  over  by  a  like  quantity  of  the  dilute  acid  added  by  means  of  a 
separating  funnel  in  such  a  manner  as  to  wash  down  the  particles  ad- 
hering to  the  sides  of  the  flask,  and  continue  the  process  until  the  distil- 
late amounts  to  360  c.c.  To  the  completed  distillate  gradually  add  a 
quantity  of  phloroglucinol  (purified  if  necessary)  dissolved  in  12% 
hydrochloric  acid  and  thoroughly  stir  the  resulting  mixture.  The 
amount  of  phloroglucinol  used  should  be  about  double  that  of  the 
furfural  expected.  The  solution  first  turns  yellow,  then  green,  and 
very  soon  an  amorphous  greenish  precipitate  appears,  which  grows 
rapidly  darker,  till  it  finally  becomes  almost  black.  Make  the  solu- 
tion up  to  400  c.c.  with  12%  hydrochloric  acid,  and  allow  to  stand 
overnight. 

Filter  the  amorphous  black  precipitate  into  a  tared  gooch  crucible 
through  an  asbestos  felt,  wash  carefully  with  150  c.c.  of  water  in  such  a 
way  that  the  water  is  not  entirely  removed  from  the  crucible  until  the 
very  last,  then  dry  for  four  hours  at  the  temperature  of  boiling  water, 
cool  and  weigh,  in  a  weighing  bottle,  the  increase  in  weight  being  reck- 
oned as  phloroglucide.  To  calculate  the  furfuraldehyde,  pentose,  or 
pentosan  from  the  phloroglucide  use  the  following  formulae  given  by 
Krober: 

a.  For  weight  of  phloroglucide  "a"  under  0.03  grm. 
Furfural   =  (a  +  o.oo52)  Xo^ijo. 
Pentoses  =  (a  +  0.005  2)  X  1.0170. 
Pentosans=  (a+o.oo52)  Xo.8949. 


b.  For  weight  of  phloroglucide  "a"  over  0.300  grm. 
Furfural    =  (a-f  0.0052)  Xo.  5180. 
Pentoses    =  (a  +  o.  0052)  X  1.0026. 
Pentosans=  (a  +  o.oo52)  Xo.8824. 


PENTOSES.  403 

For  weight  of    phloroglucide   "a"  from  0.03   to  0.300    grm.   use 
Krober's  table  (/.  Landw.,  1900,  48,  379),  or  the  following  formulae: 

Furfural  =  (a  +  o.  0052)  Xo.  5185. 
Pentoses  =  (a+o.oo52)  X  1.0075. 
Pentosans=  a  +  o.oo2  Xo.8866. 


Methyl  pentoses  (such  as  rhamnose)  are  estimated  volumetrically 
in  the  same  way  as  pentoses,  the  conversion  into  methylfurf  ural  taking 
place  quantitatively  on  distillation  of  a  methylpentose  with  hydro- 
chloric acid  in  a  current  of  steam. 

In  a  mixture  of  pentoses  and  methylpentoses,  the  total  sugar  is 
determined  by  distillation  with  hydrochloric  acid;  in  a  second  portion 
of  the  sample  the  methylpentoses  are  precipitated  by  alcohol  and  satu- 
rated aqueous  baryta  at  o°  and  the  pentoses  are  estimated  in  the 
nitrate. 


STARCH  AND  ITS  ISOMERIDES. 


E.  FRANKLAND  ARMSTRONG,  D.  Sc  ,   PH.  D.,  A.  C.  G.  I. 

In  the  vegetable  kingdom,  and  to  a  minor  extent  in  the  animal 
kingdom,  there  exist  a  number  of  carbohydrates  having  in  common  a 
composition  represented  by  the  empirical  formula  C6HIOOS,  but  their 
physical  and  chemical  characters  point  in  all  cases  to  a  multiple  of 
this  formula  as  the  true  representation  of  the  constitution  of  the 
molecule. 

The  carbohydrates  of  the  starch  group  are  non-volatile  bodies,  and, 
with  perhaps  one  or  two  exceptions,  are  amorphous.  As  a  class  they 
are  insoluble  in  alcohol,  though  the  greater  number  of  them  are  dis- 
solved by  water,  forming  solutions  which  usually  exert  a  marked  rota- 
tory action  on  a  ray  of  polarised  light.  They  are  neutral  in  reaction, 
and  form  but  few  definite  compounds  or  metallic  derivatives.  They 
are  very  numerous,  and  apparently  capable  of  isomeric  modification. 
Owing  to  their  physical  characters  and  feebly-marked  chemical  affini- 
ties, it  is  often  difficult  to  obtain  them  in  a  state  of  purity. 

None  of  the  members  of  the  group  reduces  Fehling's  solution  when 
boiled  with  it.  By  treatment  with  acids  they  undergo  hydrolysis, 
yielding  sugars  among  other  products,  and  then  reduce  the  cupric 
solution. 

Many  of  the  members  of  the  group  are  of  little  practical  interest,  and 
their  analytical  reactions  have  been  very  incompletely  studied.  The 
following  table  serves  to  show  the  comparative  characters  of  the 
more  important  members,  and  cellulose,  starch,  and  dextrin  are  des- 
cribed more  fully  in  subsequent  sections.  Elsewhere  will  be  found 
tables  for  the  general  proximate  analysis  of  plant-products,  and  under 
the  head  of  "Gums"  a  short  description  of  pectinous  matters. 

405 


406 


STARCH   AND    ITS    ISOMERIDES. 


I5|§ 

c'S  §    ^ 

K^>  cC  o3 

OJ3 
B'- 

n 
5 

^§ 

o, 

111  i 

6^H"'S 

^§ 

•o 

ii 

G  ^ 

O,  •  rt      3 

(H  *5  *2 

^  "Q 

,d 

?3  O 

G  bfi^ 

rt-S"t,    "° 

a^o  o 

53    qj 

e 

81 

Other  characters. 

Soluble  in  Schweitzer's  reagent,  f 
rotatory  solution.  With  stro 
acid,  followed  by  dilution,  gi^ 
etc. 

White  powder  of  characteristic 
under  microscope.  Insoluble 
zer's  solution.  Precipitated  b 
ammoniacal  lead  acetate. 
White  amorphous  body,  readily 
kaline  liquids. 

White,  hygroscopic  powder,  or 
tals,  Insoluble  in  absolute  a 
ingly  in  dilute.  Reduces  amn 
of  silver. 
White,  very  deliquescent.  Apr 
varieties,  differing  in  their  r 
iodine.  Insoluble  in  alcohol. 

Amorphous,  white  substance. 

Amorphous,  white  substance.  F 
exhibits  bi-rotation. 

Amorphous.  Solutions  highly 
soluble  in  alcohol.  Yield  mi 
treatment  with  nitric  acid. 

!  _,  a)  % 
•£•£  c.2 

3*31 

W            u> 

IP  His 

Is:! 

—  w-  0^ 

O.Q  cx°  o 

oi 

1     1 

Js           ** 

1 

o 
o 

/ry  th  r  o  - 
dextri  n  , 
red  dis  fa- 
brown  ;ach- 
rodext  r  i  n  , 

1! 
' 

0) 

! 

n) 
1 

0 

1 
° 

* 

>          £ 

* 

w 

* 

^ 

Z 

Products  ob- 
tained by 
boiling  with 
dilute  acid. 

Not  changed 

Maltose  and 
dextrin; 
ultimately 
dextrose. 
Dextrose. 

Laevulose. 

Dextrose. 

Dextrose. 

A  dextro- 
glucose. 

hj 

'"•o  c     i;  w*o  .    j,j. 

T3  C  o       J:  <U  <UTJ        0^ 

o 

•Sftn 

&  IIS 

0  >> 

.B 

o}«    -Sa 

*"8 

o  « 

^g. 

| 

C    .  oJ 

a     o  g  o 

rf"°d 

£lj 

."%  V 

3 

4)  0 

73+3 

So"2 

1 

S°  W 

o>    .S-S-2 

c'«  «§ 

ft 

& 

S 

1 

€ 

n  •  rt  n  C      •  rt    -  O 
3rt  S^  >^S-S  « 

llllllll^ 

£          cH 

^•5>. 

3na 

o 

>i 

'S 

s 

K 

n)       (o 

8il 

2-§5 
cS 

ll|ll 

f! 

at- 

0 

O                    '" 
N 

A^ 

8 

N 
| 

'* 

1  b 

'o  -2  ;> 

. 

II  +    •  II  + 

>  ° 

+ 

1      M 

>2 

O.+-"  O 

* 

¥fl 

1 

1' 

"               1 

w  t3 

Q                Q 

^  0 

Q 

Q 

^Q      0 

"o 

i2j          i2i 

i2. 

,51 

,2, 

. 

—  "    IH 

05  w"     s  > 

rt   w 

0)  C  U 

•32 

u 

<U    K>   G 
O  (£  2 

??l 

<U    !H                         O 

G  >> 
c«  o 

!?.?. 

111 

cj 

« 

§ 

R 

c  fe  S 

*1ci      °^ 

^Js't 

"'  ^^-2 

•  G^ln 

>> 

"rt 

11"** 

2<sJ 

g£tS    ?J§ 

HJ 

j^j'O'O  o  -g  O  O 

•c 

rt 

S 

0     *3 

o 

<         ^3 

w 

< 

« 

f 

ll 

Q 

6        5 

Q 

4 

5 

3 

. 

a  G 

G  n 

a 

W          ffi 

ffi 

ffi 

M 

PC 

w<2 

o 

o          o 

o 

U 

0 

0 

d 

§ 

G 

c" 

1 

8 
i 
% 

2 

M               S 

_c 

3 
fl 

•c 

1 

e 

a 

i 

3 

O 

STARCH.  407 

STARCH. 

Starch  is  the  characteristic  product  of  the  vegetable  kingdom;  it  is 
formed  in  almost  every  part  of  plants.  It  is  a  white,  glistening,  taste- 
less powder,  fixed  in  the  air  and  not  volatile  nor  crystallisable.  It  is 
very  hygroscopic  and  contains  when  air-dried  from  16  to  28%  of  water 
and  still  about  10%  of  water  when  dried  in  a  vacuum. 

Starch  is  not  dissolved  without  change  by  any  known  solvent  and  is 
quite  unacted  on  by  alcohol,  ether  or  cold  water.  When  heated  with 
water  to  a  temperature  which  differs  slightly  according  to  the  origin 
of  the  starch,1  the  granules  swell  up  and  form  a  paste,  and  in  presence 
of  much  water  colloidal  solutions  are  formed,  the  exact  nature  of  which 
is  still  imperfectly  understood.  It  is  more  than  probable  that  it  is  not 
a  single  substance  of  very  high  molecular  complexity,  as  generally  sup- 
posed, but  a  mixture  of  closely  related  isomerides  of  somewhat  simpler 
structure. 

On  hydrolysis  with  dilute  acids,  starch  is  converted  into  a  mixture 
of  dextrins  and  maltose;  prolonged  treatment  results  in  further  hy- 
drolysis and  ultimate  complete  conversion  into  dextrose.  A  solution  of 
starch  is  hydrolysed  by  malt  extract  (diastase}  to  dextrin  and  maltose 
even  in  the  cold;  solid  starch  is  not  attacked  by  malt  extract  unless  a 
liquefying  enzyme  be  also  present.  The  saliva  ferment  also  hydrolyses 
starch. 

Soluble  starch  is  produced  by  boiling  starch  with  water;  the 
solution  obtained  may  be  rendered  quite  clear  by  the  addition  of  a 
little  caustic  alkali.  It  is  the  first  product  of  the  action  of  dilute  acids 
or  ferments  on  starch.  To  prepare  it  the  Malt  Analysis  Committee 
(see  under  Malt)  advise  digesting  purified  potato  starch  with  dilute 
hydrochloric  acid  (sp.  gr.  1.037)  a*  60-65°  F.  for  7  days. 

Soluble  starch  is  a  very  perfect  colloid  and  has  a  high  viscosity.  It  is 
strongly  dextrorotatory. 

Parow,  Ellrodt,  and  Neumann  (Zeit.  Spiritusind.,  1907,  30,  432) 
give  the  following  mean  results  for  the  specific  gravities  of  various 
starches. 

'The  gelatinisation  temperatures  are  as  follows: 

Green  malt  and  oat  starch,  85°  C. 

Barley,  kilned  malt,  rye,  wheat  and  rice  starch,  80°  C. 
Maize  starch,  75°  C. 

Potato  starch,  65°  C. 


408 


STARCH   AND    ITS    ISOMERIDES. 


Sp.  gr.  of  anhy- 

OLJ.    HI  .     \J*.     HVUi<*Lf-L     OLCIH-1J     111. 

drous  starch  in: 

Water 

Toluene 

Starch  from: 

Per  cent. 

Per  cent. 

Water 

Toluene 

of  water 
in  the 

Sp.  gr. 

of  water 
in  the 

Sp.  gr. 

starch 

starch 

f 

18.72 

•463 

Potatoes, 

1.648 

I-5I3- 

19-35 

-436 

'    i5-03 

i  .361 

20.14 

•453 

I3-38 

•515 

Wheat, 

i  .629 

1.502 

13.80 

.496 

'    13  '90 

1-365 

14.60 

.492 

ii  .06 

.522 

Maize, 

i  .623 

1-499 

12.88 

•504 

12.60 

1-378 

14.36 

.490 

r 

11.92 

-514 

Rice, 

i  .620 

1.504 

13  .  10 

.500 

•    14-03 

i  .360 

I 

14.14 

.501 

Structure  of  Starch  Corpuscles. — Starch  occurs  in  plants  in  the 
form  of  minute  granules,  which  generally  possess  a  concentrically  strati- 
fied structure  similar  to  that  of  an  onion.  These  granules  consist 
chiefly  of  a  body  called  granulose,  together  with  a  closely  allied  sub- 
stance known  as  amylo-cellulose  or  starch-cellulose,  and  water  and 
traces  of  mineral  matter.  Starch-cellulose  occurs  in  largest  propor- 
tion in  the  outer  layers  of  the  granule,  and  probably  constitutes  the 
whole  of  the  external  coating.  Owing  to  this  protective  coating,  starch 
granules  are  wholly  unacted  on  by  cold  water,  as  the  internal  granu- 
lose, though  slightly  soluble,  is  highly  colloidal.  When  the  outer 
layer  of  the  granule  is  ruptured,  as  by  grinding  the  starch  with  sand, 
water  acts  readily  on  it,  and  the  liquid  gives  an  intense  blue  colour  with 
iodine.  By  treating  starch  paste  with  malt-extract,  the  insoluble 
starch-cellulose  may  be  obtained  pure,  and  then  is  found  to  give  only  a 
dirty  yellow  colour  with  iodine.  Saliva  (owing  to  the  ptyalin  con- 
tained in  it)  and,  at  a  temperature  of  50°  to  60°  pepsin,  organic  acids, 
very  dilute  hydrochloric  or  sulphuric  acid,  and  a  saturated  solution 
of  sodium  chloride  containing  i%  of  hydrochloric  acid,  all  dissolve 
out  the  granulose  and  leave  the  amylo-cellulose  intact.  By  boiling 
with  water,  starch-cellulose  is  mostly  converted  into  soluble  starch, 


STARCH.  409 

leaving,  however,  a  portion  which  obstinately  resists  the  action  of  water, 
but  is  readily  dissolved  by  dilute  alkali.  Amylo-cellulose  differs  from 
ordinary  cellulose  in  being  insoluble  in  Schweitzer's  reagent.  By 
repeated  alternate  treatment  of  potato-starch  in  the  cold  with  very  dilute 
alkali  and  acid,  the  cellulose  may  be  removed,  when  the  residue  dis- 
solves in  hot  water  to  form  a  perfectly  clear  solution.  Solid  starch  cor- 
puscles, when  treated  with  iodine  solution,  are  coloured  intensely  blue, 
the  reagent  readily  penetrating  the  coating  of  cellulose  and  thus  reach- 
ing granulose. 

Young  small  corpuscles  of  starch  appear  to  be  invariably  spherical, 
but  as  they  grow  older  they  may  become  lenticular,  ovoid,  or  polyg- 
onal. The  shape  and  size  of  the  starch  corpuscles  are  often  highly 
characteristic  of  the  plant  by  which  they  were  produced,  and  this 
fact  is  frequently  taken  advantage  of  for  identifying  the  presence  of 
starch  from  particular  sources. 

Microscopic  Identification  of  Starches. — When  a  sample  is  to 
be  examined  under  the  microscope  for  the  identification  of  its  starch, 
a  minute  quantity  should  be  placed  on  a  glass  slide  with  the  point  of 
a  knife.  If  in  a  powdered  state,  or  readily  reducible  to  powder,  a 
preferable  plan  is  to  stir  the  sample  with  a  dry  glass  rod,  and  tap  the 
rod  on  the  glass  slide.  A  drop  of  distilled  water  or  diluted  glycerol 
(i  of  glycerol  to  2  of  water)  should  then  be  added,  and  if  the 
unpowdered  structure  be  employed  it  should  be  broken  up  by 
careful  crushing  with  the  point  of  a  knife.  A  glass  cover  is  then 
put  on,  and  any  superfluous  moisture  removed  by  blotting-paper. 
The  specimen  is  now  ready  for  observation.  Somewhat  oblique 
light  should  always  be  employed,  and  the  power  should  be  about  200 
diameters. 

The  points  to  be  observed  in  the  microscopic  observation  of  starches 
are:  (a)  The  shape  and  size  of  the  granules,  (b)  The  position  and 
character  of  the  hilum.  (c)  The  concentric  markings,  (d)  The  ap- 
pearance under  polarised  light.  The  first  two  observations  are  toler- 
ably simple,  but  the  examination  for  rings  requires  care,  the  markings 
being  rarely  visible  without  very  cautious  manipulation  of  the  illumi- 
nation and  movement  of  the  fine-adjustment,  and  then  only  in  a  few 
granules  at  the  same  time.  Natal  arrowroot  and  turmeric  starches 
show  well-developed  rings  on  nearly  every  granule.  Wheat,  on  the 
other  hand,  shows  few  rings,  even  in  the  best  light.  When  the  hilum 
is  situated  near  the  centre  of  the  granule,  the  rings  are  usually  complete, 


410  STARCH   AND    ITS    ISOMERIDES. 

but  when  the  hilum  is  near  one  end  of  the  granule  only  a  segment  of 
each  ring  is  visible. 

Although  the  size  of  starch-granules  is  a  highly  important  character, 
it  must  be  remembered  that  great  difference  is  often  noted  between 
individual  granules,  and  that  it  is  only  the  general  or  average  size  of  the 
corpuscles  which  is  usually  recorded.  Difference  in  size  of  the  starch- 
granules  is  very  marked  in  the  case  of  the  potato,  in  which  the  corpus- 
cles range  from  0.0025  °f  an  mcn  in  length  down  to  less  than  0.0002 
(0.063  millimetre  to  less  than  0.005). 

Examination  with  polarised  light,  either  with  or  without  the  use  of  a 
selenite  plate,  is  a  valuable  auxiliary  means  of  identifying  starches,  but 
many  of  the  statements  made  in  books,  such  as  the  black  cross  being 
observable  in  the  case  of  certain  starches  only,  must  be  considered  as 
merely  applicable  to  the  precise  conditions  under  ,which  the  observa- 
tions referred  to  were  made.  With  proper  manipulation,  all  starches 
appear  to  show  the  black  cross,  and  an  ignorance  of  this  fact  has  led 
many  into  error.  Some  starches  show  much  more  colour  than  others 
when  examined  under  the  polarising  microscope.  For  observation  of 
starches  by  polarised  light  it  is  often  desirable  to  employ  a  highly- 
refracting  mounting  medium,  and  for  such  purposes  water  may  be 
advantageously  replaced  by  diluted  glycerin,  glycerol  jelly,  Canada 
balsam,  oil  of  anise,  carbon  disulphide,  etc. 

Much  has  been  written  on  the  microscopic  appearance  of  starches, 
and  some  observers  profess  to  be  able  to  distinguish  starch  of  almost 
every  origin.  To  the  observer  who  has  not  made  a  special  study  of 
the  morphology  of  starches,  these  distinctions  are  in  many  cases  wholly 
unrecognisable,  and  as  the  minute  points  of  difference  are  almost  in- 
capable either  of  description  or  delineation,  the  only  safe  method  of 
discriminating  starches  is  by  a  careful  comparison  of  the  sample  with 
specimens  of  known  origin  and  purity,  making  the  observations  under 
exactly  similar  conditions  as  to  illumination,  magnifying  power  and 
mounting  medium.  These  standard  specimens  should  not  be  perma- 
nently mounted,  but  kept  in  an  air-dry  state,  and  a  minute  quantity 
mixed  with  water  or  other  medium  when  required  for  use.  As  a  rule, 
it  is  quite  unnecessary  to  prepare  the  pure  starches  for  comparision,  a 
direct  employment  of  the  air-dried  tissue  answering  every  purpose. 

Very  complete  tabular  schemes  for  the  recognition  of  starches  by 
the  microscope  have  been  devised  by  Muter  (Organic  Materia  Medico), 
but  a  later  work  is  that  of  Greenish,  Microscopical  Examination  of  Foods 


STARCH.  411 

and  Drugs.  Of  course,  they  in  no  way  enable  the  observer  to  dispense 
with  the  requisite  experience  in  observation,  but  they  much  facilitate 
the  recognition  by  drawing  attention  to  the  more  characteristic  features 
of  the  starches.  The  figures  of  starch  granules  on  pages  414  to  416 
are  derived  from  Greenish 's  book.  They  first  appeared  in  the 
Pharmaceutical  Journal. 

The  following  arrangement  of  starches,  according  to  their  micro- 
scopic appearance,  is  based  on  that  of  Muter.  The  starches  are 
arranged  in  5  classes.1 

I.  The  potato  group  includes  such  oval  or  ovate  starches  as  give 
a  play  of  colours  when  examined  by  polarised  light  and  a  selenite  plate, 
and  having  the  hilum  and  concentric  rings  clearly  visible. 

II.  The    leguminous    starches    comprise   such   round    or   oval 
starches  as  give  little  or  no  colour  with  polarised  light,  have  concentric 
rings  all  but  invisible,  though  becoming  apparent,  in  many  cases,  on 
treating  the  starch  with  chromic  acid,  while  the  hilum  is  well  marked, 
and  cracked  or  stellate. 

III.  The  wheat   group   comprises  those  round  or  oval  starches 
having  both  hilum  and  concentric  rings  invisible  in  the  majority  of 
granules.     It  includes  the  starches  from  wheat  and  some  other  cereals, 
and  a  variety  of  starches  from  medicinal  plants,  such  as  jalap,  rhubarb, 
senega,  etc. 

IV.  The  sago  group  comprises  those  starches  of   which  all   the 
granules  are  truncated  at  one  end.     It  includes  some  starches  used  for 
food,  together  with  those  from  belladonna,  colchicum,  scammony, 
podophyllum,  canella,   aconite,  cassia,   and  cinnamon. 

V.  The  Rice  Group  contains  the  starches  all  the  granules  of  which 
are  polygonal  in  form.     It  includes  the  starches  from  oats,  maize,  buck- 
wheat, rice,  pepper,  and  ipecacuanha. 

The  following  table  gives  further  particulars  respecting  the  micro- 
scopic appearance  of  the  more  important  starches.  The  figures 
expressing  the  sizes  are  micro-millimetres  (i/ioooth  millimetre,)  but 
they  may  be  converted  into  ten-thousandths  of  an  inch  by  multiplying 
them  by  the  factor  0.3937. 

In  the  case  of  elongated  starches,  the  figures  expressing  the  size  have 
reference  to  the  mean  of  the  longer  and  shorter  diameters. 

JIn  order  that  mistakes  may  not  be  made  in  differentiating  starches  by  the  scheme,  it  is 
important  to  bear  in  mind  that  the  appearances  described  apply  to  the  following  conditions 
of  examination,  namely,  observation  with  oblique  light;  use  of  water  as  a  medium,  and, 
when  polarised  light  is  used,  the  use  of  a  red-green  selenite  plate  with  diluted  glycerol  as  a 
mounting  medium. 


412 


STARCH   AND    ITS    ISOMERIDES. 


Diam- 


metres. 


CLASS  I. 

Canna,  or 

47-132 

Irregular    oval,    or    Hilum      annular     and      eccenfic. 

tous-les- 

oyster-shaped.              Rings     incomplete,      very     fine, 

mois. 

(Fig.  59-) 

narrow,  and  regular.     Alkali  de- 

velops   lines    and  hilum.     Well- 

marked   and   regular  cross   with 

polarised  light. 

Potato. 

Very 

Small  granules,  cir-     Hilum,  a  spot,  generally  near  small- 

variable; 

cular;  the  larger        er  end.     Rings  in  larger  granules 

usually 

ovate,   or  oyster-        numerous    and    complete.     Very 

between 

shaped.  (Fig.  60.)  j       distinct  cross  towards  smaller  end, 

60  and 

and  brilliant  colours  with  polar- 

100 

ised  light. 

Maranta- 

loto  70 

Somewhat  ovoid  or    Hilum,  near  one  end,  either  circular 

arrowroot. 

average 

mussel-shaped,        or    linear,    and    often    cracked. 

36 

tendingtotriangu-        Rings  numerous  and  always  visi- 

lar  in  larger  gran-  j       ble,    but    not    strongly    marked  . 

ules.     Sometimes        Well-defined  cross  towards  larger 

irregular,   with  a        end  with  polarised  light,  and  bril- 

nipple-like     pro-l       liant  colours. 

jectionatsameend 

as  hilum.  (Fig.6i) 

Natal-arrow- 

33 to  38 

Broadly    ovate,    or!  Hilum,  a  crack,  eccentric.     Rings 

root. 

occasionally    cir-        very  distinct  under  water. 

cular,  with  irreg- 

ular projections,    j 

Curcuma- 

30  to  61 

Resemblesmaranta.  I  Hilum,  an  eccentric  dot  or  circle. 

arrowroot. 

Elongated,  oroval 

Indistinct     segments     of     rings. 

with  irregular  pro- 

Heat or  alkali  deforms  granules 

jection.  (Fig.  62.) 

very  irregularly. 

CLASS  II. 

Bean. 

Nearly 

Reniform  or  oval. 

Hilum,    stellate.     Often    becoming 

uniform 

a   longitudinal   furrow.     Smaller 

3°  to  35 

granules  predominate. 

Pea. 

Very 

Reniform    or   oval. 

Hilum  elongated.  Not  distinguish- 

variable 

able  from  bean  in  mixtures. 

20  to  40 

Lentil. 

20  to  40 

Reniform  or  oval. 

Hilum  elongated  and  very  clearly  de- 

fined.   Rings  moderately  distinct. 

CLASS  III. 

Wheat. 

Very 

Circular   or   nearly 

Chiefly  of  two  sizes,  large  and  very 

variable 

so,  and  flattened. 

small.     Shows  a  cross  in  glycerin 

2  to  52 

'Fig.  63.) 

with    polarised    light,    but    very 

slightly    in    water.     Faint    rings 

and  colours  are  visible  on  the  most 

elliptical  granules. 

Barley. 

Fairly 

Closely      resembles 

Not  certainly  distinguishable  from 

uniform 

wheat;  some  gran- 

wheat  in   mixtures   of  the   two. 

13  to  39 

ules  slightly  angu- 

lar,  or   elliptical. 

(Fig.  64.) 

STARCH. 


413 


Diam- 
Ongin  of        eter  in     Characteristic  shape 
starch            micro-            of   granules, 
milli- 
metres. 

Other  characters. 

Rye. 

2  to  38      Closely  resembles 

A  few  granules  show  a  three-  or  four- 

wheat.   (Fig.  65.) 

armed    fissure    extending    nearly 

to  the  circumference. 

Oat. 

Large  oval  granules 

The  compound  granules  break  up  by 

showing  p  o  1  v  g- 

attrition  into  polygonal  granules 

onal    divisions. 

(see  Class  V.). 

(Fig.  66.) 

Acorn.                   19           Circular  or  slightly 

Eccentric  hilum  developed  by  chro- 

oval. 

mic  acid. 

CLASS  IV. 

Arum.                   14 

Truncated  with  two 

Hilum  eccentric. 

facets. 

Tacca-             9  to  19 

Resembles  tapioca.     Distinct    hilum,    linear    and    often 

arrowroot. 

starred.     Very  varied  shape,  often 

resembling  maize,  but  has  sharp 

angles. 

Sago. 

25  to  66 

Ovate,  or  truncated 

Hilum,  a  circular  spot  or  crack  at 

oval.  (Fig.  67.)            convex  end;   faint  rings.     Well- 

defined   cross,  and  often  colours 

with    polarised    light.     Prepared 

' 

sago  shows  large  oval  depression; 

with    polarised    light    characters 

less  definite  than  the  raw. 

Tapioca.          8  to  22 

Kettle-drum,  or  cir-    Hilum,  a  dot  or  short  slit,   nearly 

cular.     (Fig.  68.)         central.     Well-defined  cross  and 

colours    with    polarised     light. 

Characters    of    prepared    tapioca 

are  less  definite. 

CLASS  V. 

Rice.              1  5  to  8 

Pentagonal  or  hex-    Angles    sharply    defined.     Distinct 

agonal,  occasion-         hilum  with  a  very  high  power,  and 

ally   triangular.            cross   visible   in    larger   granules 

\Fig.  69.)                      with  polarised  light. 

Buckwheat.        5  to  20 
depend- 

Resembles  oat  and    No  rings,  but  distinct  central  hilum, 
rice,    but    angles        as    spot    or    star.     Well-defined 

ing  on 

more  rounded.             cross,  with  polarised  light.    Gran- 

variety 

ules  often  compound. 

Oat. 

4  to  30 

Triangular  to  hexag-     Rings     and     hilum     invisible     ex- 

onal,  a  few  small        cept    under    very    high    powers. 

and       round      or        Faint    cross    by    polarised    light. 

apple-pip-shaped. 

Maize. 

7  to  20 

Circular  to  polyhe-     Hilum    central,    as    a    well-defined 

dral,  usually,  with         star  or  crack.     Rings  nearly  in- 

rounded     angles.         visible.     Distinct  cross  and  faint 

(Fig.  70.)                      colours  with  polarised  light. 

Dari.                      19          Small  elongated 

hexagons. 

Pepper.             i  to  5 

Resembles  rice,  but    Shows  hilum  with  very  high  power. 

majority  d  e  c  i  d  -         Granules  often  in  motion.  Forms 

edly  smaller.                  large  compound  granules  of  very 

irregular  form. 

414 


STARCH. 


FIG.  59. — Tous-les-mois  starch  X  240.     (Greenish.) 


FIG.  60. — Potato  starch  X  240.     (Greenish.} 


STARCH   AND    ITS    ISOMERIDES. 


415 


^*&>'j    ^avSw^lai 

tf«rall.    wl 


FiG.  61. — Maranta  starch  X  240. 
(Greenish.) 


FIG.  62. — Curcuma  starch  X  240. 
(Greenish.) 


»VA.  £•&?£)  • 


?K7t>. 


0&  (    l%°^'£vj£A  Q°(Y       ^3  °  o  o  <r\  o>f .  «/^c 

_  o  °  \^     .bilr~   -    X^<y         ° 3      ^   /  1  ^  v J 


<j  ^^^^  -  /•        ,      \^>^-    -  g    -*^j^^-        ^T^ 

o°.oc%^*07'/oo0»O  0^ 

FIG.  63. — Wheat  starch  X  240. 
(Greenish.) 


£.C. 


FIG.  64. — Barley  starch  X  240. 
( Green  wA. 


^t^'owr/^i 


'°  fl-o4m9()^^ 

>B^H^^59 

^c3 

FIG.  65. — Rye  starch  X  240.  FIG.  66. — Oat  starch  X  240. 

(Greenish.) 


STARCH   AND    ITS    ISOMERIDES. 


FIG.  67. — Sago  starch  X  240. 
(Greenish.) 


FIG.  67  a. — Sago  X  240. 
(Greenish.) 


SR. 

/v*y\  ^m 
wwy  V  :£?'')  ^ 


%*w 

» 


f  C 


FIG.  68. — Tapioca  starch  X  240. 
(Greenish.) 


FIG.  68  a. — Tapioca  X  240. 
(Greenish.) 


o; 


0 

o 
00 


PtRO 


o  o 


o^tf? 

D 


o^lS^^MIl 


CO 


FIG.  69. — Rice  starch  X  240 
(Greenish.) 


FIG.  70. — Maize  starch  X  240. 
(Greenish.) 


STARCH.  417 

Arrowroot  of  commerce  is  the  starch  derived  from  plants  of  the 
genus  Maranta,  belonging  to  the  order  Marantaceu'.  For  trade  pur- 
poses arrowroot  is  distinguished  by  the  name  of  the  island  or  country 
producing  it. 

The  starch  corpuscles  of  the  different  species  and  varieties  of  Maranta 
differ  considerably  in  their  microscopic  appearance,  while  certain  va- 
rieties are  closely  simulated  by  the  starches  from  plants  other  than  the 
different  species  of  Maranta.  This  is  the  case  with  the  starch  of 
Curcuma  angustifolia,  sometimes  called  East  Indian  arrowroot. 

Arrowroot  is  liable  to  adulteration  with  a  variety  of  cheaper  starches, 
though  the  practice  is  now  far  less  common  than  formerly.  The 
principal  starches  which  have  been  employed,  either  as  substitutes  for 
arrowroot  or  for  mixing  therewith,  have  been  those  of  potato,  sago, 
tapioca,  curcuma,  and  tous-les-mois.  Tacca  and  arum  starches  are 
also  stated  to  have  been  employed,  but  they  are  not  known  at  present 
in  the  English  market. 

The  microscope  affords  the  only  satisfactory  means  of  distinguishing 
maranta  starch  from  the  starches  above  mentioned,  and  even  then  the 
detection  of  certain  admixtures  is  a  matter  of  considerable  difficulty. 
Potato l  and  tous-les-mois  starches  are  distinguished  by  their  large  size 
and  regular  and  well-developed  concentric  rings,  and  potato,  in  addi- 
tion, by  the  hilum  being  situated  near  the  smaller  end  of  the  granules. 
Sago,  tacca,  arum  and  tapioca  are  distinguished  by  the  truncation  of 
the  granules.  Curcuma  starch  forms  oblong  irregular  granules 
rounded  at  the  posterior  extremity  but  which  often  taper  rather 
abruptly  at  the  other.  The  grains  are  so  flat  that  when  viewed  on 
their  edges  they  appear  rod  shaped. 

The  cereal  starches  may  be  divided  into  two  well-defined  groups, 
wheat,  barley  and  rye  starches  being  circular  or  nearly  so,  while  the 
starches  of  rice,  maize,  buckwheat  and  oat  are  polygonal. 

The  leguminous  starches  present  very  close  resemblances  and 
are  generally  indistinguishable  from  each  other  when  in  admixture. 

Proportion  of  Different  Starches  in  Admixture. — The  following 
method2  is  the  most  suitable,  for  ascertaining  the  extent  to  which  oat- 
resides  its  microscopical  appearance,  potato  starch  is  said  to  be  distinguished  from 
maranta  starch  in  the  following  respects:  i.  When  mixed  with  twice  its  weight  of  strong 
hydrochloric  acid,  maranta  starch  produces  an  opaque  white  paste,  while  the  paste  pro- 
duced by  potato  starch  is  transparent  and  jelly-like.  2.  Potato  starch  evolves  a  peculiar 
and  disagreeable  odour  when  boiled  with  dilute  sulphuric  acid.  3.  An  acrid  oil  may  be  ex- 
tracted from  potato  starch,  but  not  from  that  of  maranta. 

2Dr.  James  Bell  gives  the  following  method  for  estimating  starches  in  admixture:  "The 
sample  is  first  rubbed  in  a  mortar  and  passed  several  times  through  a  sieve.  A  small  quan- 
tity, say  0.003  grin.,  is  then  weighed  out  and  placed  on  a  glass  slide,  where  it  is  worked  into  a 

VOL.  1—27 


41 8  STARCH   AND    ITS    ISOMERIDES. 

meal  is  mixed  with  barley  or  wheat-flour,  and  is  a  type  of  the  process  to 
be  employed  in  other  cases.  Genuine  pearl-barley  is  ground  finely  in 
a  mortar,  and  a  series  of  standards  made  by  mixing  the  flour  with  defi- 
nite proportions  of  genuine  oatmeal.  Mixtures  containing  5, 10, 15,  20, 
30  and  40%  of  barley,  respectively,  will  be  found  convenient  in  practice. 
The  sample  of  oatmeal  to  be  examined  is  thoroughly  mixed,  and  o.i 
grm.  weighed  out  and  ground  in  an  agate  mortar  with  a  little  water. 
When  the  mixture  is  perfectly  smooth  it  is  rinsed  into  a  small  conical 
glass,  and  diluted  with  water  to  10  c.c.  Two  of  the  standard  mix- 
tures (say  the  10  and  20%  mixtures)  are  then  treated  in  a  precisely 
similar  manner.  A  drop  of  the  sample  and  one  of  each  of  the  stand- 
ards are  then  placed  on  glass  slides  and  covered  with  thin  covers. 
Care  must  be  taken  that  the  starches  and  water  are  thoroughly  agitated, 
so  that  the  drops  taken  shall  be  representative,  and  it  is  important  that 
the  drops  themselves  shall  be  of  exactly  the  same  size.  These  condi- 
tions are  best  insured  by  immersing  in  the  liquid  a  short  piece  of  glass 
tube  drawn  out  to  a  fine  point,  blowing  down  it  so  as  to  mix  the  sample 
thoroughly  by  means  of  the  air-bubbles  expelled,  and  then  allowing  a 
drop  of  the  liquid  to  fall  from  the  orifice  on  to  the  glass  slide.  The 
same  tube  is  then  employed  to  take  drops  of  the  standard  mixtures. 
The  cover-glasses  must  all  be  of  equal  size  and  sufficiently  large  to  take 
up  the  whole  of  the  drop,  as  none  of  the  liquid  must  be  removed. 
The  slides  being  prepared,  the  number  of  barley  granules  visible  in 
twelve  successive  fields  is  noted.  The  standards  are  then  similarly 
observed,  the  operation  being  repeated  until  a  standard  mixture  is 
found,  the  barley  granules  in  twelve  fields  of  which  are  equal  or 
nearly  equal  in  number  to  those  counted  in  the  sample.  The  propor- 
tion of  wheat  or  barley  in  the  sample  will  then  be  approximately  the 
same  as  that  in  the  standard  it  agrees  with. 

Detection  and  Estimation  of  Starch. — For  the  detection  of  starch 
existing  in  the  solid  state,  no  method  is  so  good  as  the  microscopic 
recognition  of  the  corpuscles,  the  origin  of  which  may  usually  be  iden- 
tified in  the  manner  already  described.  The  microscopic  examination 
may  be  advantageously  supplemented  by  adding  a  drop  of  iodine  solu- 
tion to  the  slide,  when  each  of  the  true  starch  granules  will  assume 

thin  paste  with  about  2  drops  of  water.  A  thin  covering  glass,  measuring  about  1.5  in.  by 
i  in.,  is  then  placed  over  the  paste,  and  moved  about  the  slide  until  the  paste  is  equally  dis- 
tributed and  all  under  the  covering  glass.  The  number  of  granules  is  counted  in  nine  fields, 
as  fairly  as  possible  representing  the  entire  slide.  The  process  is  repeated  till  a  correct  idea 
of  the  composition  of  the  sample  is  obtained.  Standard  mixtures  approximately  represent- 
ing the  sample  are  made  up  and  treated  in  exactly  the  same  way,  and  from  a  comparison 
of  the  results  the  percentage  of  foreign  starch  is  computed." 


STARCH.  419 

a  blue  colour,  which  renders  their  recognition  easy.  In  some  cases, 
as  when  roasted  coffee  is  mixed  with  beans  or  acorns,  the  microscopic 
detection  of  the  starch  becomes  difficult,  but  may  still  be  effected  in  the 
following  manner:  The  coffee  is  boiled  with  water  for  a  few  minutes, 
and  the  solution  is  decanted  or  filtered  from  the  insoluble  matter. 
The  liquid  is  next  thoroughly  cooled  and  cold  dilute  sulphuric  acid  is 
added.  A  solution  of  potassium  permanganate  is  then  gradually 
added  till  the  brown  colour  is  nearly  or  entirely  destroyed,  when  the 
decolorised  liquid  is  tested  with  iodine.  A  blue  colour  is  obtainable  in 
this  way  with  coffee  containing  only  i  per  cent,  of  roasted  acorns. 

Sometimes  it  is  desirable  to  remove  the  colouring  matter  from  the 
solid  substance  before  examining  it  for  starch.  If  cold  water  fail  to 
effect  this,  alcohol  should  be  tried,  and  subsequently  other  solvents. 
The  cases  are  rare,  however,  in  which  the  starch  cannot  be  observed 
microscopically  after  successive  treatments  of  the  substance  with  cold 
water  and  alcohol. 

In  aqueous  solution,  starch  yields  a  precipitate  with  ammoniacal 
lead  acetate  having  a  composition  represented  approximately  by  the 
the  formula  CiaHr?Pb2O1I.  Tannin  gives  a  white  precipitate  with 
starch  solution,  disappearing  on  warming  and  reappearing  as  the  liquid 
cools.  Soluble  starch  is  completely  precipitated  by  adding  alcohol  to 
its  aqueous  solution. 

The  most  characteristic  reaction  of  starch  solution  is  the  violet  or 
indigo-blue  colouration  which  it  gives  with  iodine.  The  coloured  sub- 
stance does  not  appear  to  be  a  definite  compound  of  starch  with  iodine,  a 
and  hence  is  best  called  iodised  starch.  The  best  form  in  which  to  em- 
ploy the  reagent  is  as  a  very  dilute  solution  of  iodine  in  potassium  iodide. 
The  starch  solution  should  be  perfectly  cold.  On  heating  the  liquid 
it]  is  decolourised,  but  on  cooling  the  blue  is  restored,  though  not  with 
the  same  intensity  as  before.  In  employing  the  reaction  as  a  test 
for]  starch  it  is  necessary  to  remember  that  it  is  only  produced  by  free 
iodine.  Hence  any  free  alkali  should  be  neutralised  by  cautious  addi- 
tion of  cold  dilute  acid,  and  any  reducing  or  oxidising  agent  got  rid  of 
if 'possible.  The  best  way  of  testing  for  starch  is  to  add  the  iodine 
solution  gradually  to  the  slightly  acid  liquid  until  either  a  blue  appears 
or  the  liquid  remains  permanently  yellow  by  the  free  iodine.  If  the 
latter  effect  is  produced  and  yet  no  blue  is  obtained  no  starch  can  be 
present. 

The  only  organic  compound  liable  to  interfere  when  the  test  is  per- 


420  STARCH   AND    ITS    ISOMERIDES. 

formed  in  the  foregoing  manner  is  ery throdextrin,  which  itself  produces 
an  intense  reddish-brown  colouration  with  iodine,  which  is  apt  to  mask 
a  feeble  starch-reaction.  The  affinity  of  iodine  for  starch  is,  however, 
greater  than  its  affinity  for  erythrodextrin,  and  hence  if  a  very  little 
iodine  solution  be  employed  the  blue  due  to  starch  will  alone  be  de- 
veloped, the  brown  becoming  apparent  on  a  further  addition  of  the  re- 
agent. By  cautiously  adding  very  dilute  ammonia  or  gradually  heating 
the  liquid,  the  brown  colour  can  be  destroyed  while  the  blue  remains.1 

Estimation  of  Starch. — The  accurate  estimation  of  starch  is  a 
difficult  matter. 

Chemical  Methods. — These  are  based  on  the  hydrolysis  to  reducing 
sugar  by  means  of  acids  or  enzymes  and  estimation  of  this  either 
by  means  of  its  cupric  reducing  or  optical  powers  or  by  fermenta- 
tion to  alcohol.  In  presence  of  vegetable  tissue  containing  pentosans 
or  other  carbohydrates  which  yield  reducing  sugars  on  hydrolysis  the 
acid  method  gives  untrustworthy  results,  but  it  is  applicable  to  the 
assay  of  commercial  starches. 

Hydrochloric  Acid  Method  (as  adopted  by  the  A.  O.  A.  C.).— 
3  grm.  of  the  material  are  extracted  with  50  c.c.  of  cold  water  for 
an  hour  with  frequent  stirring.  The  residue  is  collected  on  a  filter 
and  washed  with  water  sufficient  to  bring  the  filtrate  up  to  250  c.c. 
If  the  solution  is  difficult  to  filter,  2  c.c.  of  alumina  cream  are  added. 
The  soluble  carbohydrates  are  determined  in  the  filtrate  both  before 
and  after  inversion.  The  insoluble  residue  is  heated  for  21/2  hours 
with  200  c.c.  of  water  and  20  c.c.  of  hydrochloric  acid  (sp.  gr.  1.125) 
in  a  flask  with  a  reflux  condenser,  cooled,  nearly  neutralised  with 
sodium  carbonate  or  sodium  hydroxide  made  up  to  250  c.c.,  filtered 
and  the  dextrose  determined  in  an  aliquot  portion  of  the  filtrate.  The 
weight  of  dextrose  multiplied  by  0.9  gives  the  weight  of  starch. 

Diastase  Method. — This  method  which  was  originated  by  C. 
O'Sullivan  in  1884  (Trans.,  1884,  45,  i)  is,  on  the  score  of  accu- 
racy, by  far  the  best  which  has  hitherto  been  proposed,  but  it  is  in- 
convenient owing  to  the  length  of  time  required  to  extract  the 
amylans  thoroughly. 

The  finely-divided  grain  is  extracted  with  ether  to  remove  fats,  with 
alcohol  to  separate  sugars  and  washed  with  water  to  remove  amylans. 
The  residue  is  transformed  by  diastase  into  maltose  and  dextrin,  the 

1  Neither  the  brown  colour  of  a  solution  of  iodised  erythrodextrin  nor  the  blue  of  iodised  ' 
starch  shows  absorption  bands  when  examined  by  the  spectroscope. 


STARCH.  421 

proportions  of  which  are  determined  by  Fehling's  solution  and  by  the 
polariscope.  A  fair  sample  of  the  grain  is  taken  and  5.1  gem.  weighed 
roughly  and  ground  to  a  fine  flour  in  a  clean  coffee-mill.  5  grm.  of 
the  powder  are  placed  in  a  flask  of  about  120  c.c.  capacity  thoroughly 
wetted  with  rectified  spirit,  and  25  c.c.  of  ether  added.  The  flask  is 
corked  and  agitated  occasionally,  and  after  a  few  hours  the  ether  is 
decanted  through  a  filter  and  the  residue  washed  by  decantation  with 
three  or  four  fresh  quantities  of  ether.  To  the  residue  80  to  90  c.c. 
alcohol,  sp.  gr.  0.90,  are  added,  and  the  mixture  kept  at  35°  to  38°  for 
a  few  hours  with  occasional  shaking.  The  alcoholic  solution,  when 
clear,  is  decanted  through  the  filter  used  in  filtering  the  ethereal  solu- 
tion, and  the  residue  washed  a  few  times  by  decantation  with  alcohol  of 
the  strength  and  at  the  temperature  indicated.  The  residue  in  the 
flask  and  any  little  that  may  have  been  decanted  on  to  the  filter,  is  then 
treated  with  about  500  c.c.  of  cold  water.  In  about  24  hours  the 
supernatant  liquid  becomes  clear,  when  it  can  be  gradually  decanted 
through  a  filter.  The  solution  filters  bright,  but,  in  the  case  of  barley 
and  oats,  exceedingly  slowly  at  times;  the  malted  grains,  as  well  as  wheat, 
rye,  maize,  and  rice,  yield  solutions  requiring  no  excessive  time  to  filter. 
The  residue  is  repeatedly  washed  with  water  at  35°  to  38°,  but  this 
treatment  does  not  completely  free  barley  and  oats  from  a-amylan, 
which  body  dissolves  with  the  greatest  difficulty  at  this  temperature. 
The  residue  is  then  transferred  to  a  100  c.c.  beaker,  and  the  portion 
adhering  to  the  filter  washed  off  by  opening  the  filter-paper  on  a  glass 
plate  and  removing  every  particle  by  means  of  a  camePs-hair  brush,  cut 
short,  and  a  fine-spouted  wash-bottle.  When  the  transference  is  com- 
pleted, the  beaker,  which  should  not  now  contain  more  than  40  to  45 
c.c.  of  the  liquid,  is  heated  to  100°  for  a  few  minutes  in  the  water-bath, 
care  being  taken  to  stir  wrell  when  the  starch  is  gelatinising  to  prevent 
" balling"  or  unequal  gelatinisation.  After  this  the  beaker  is  cooled 
to  about  62°,  and  0.025  to  0.035  grm-  diastase,1  dissolved  in  a  few  cubic 
centimetres  of  water,  added. 

!The  diastase  employed  is  prepared  as  follows:  Two  or  3  kilogrm.  of  finely-ground  pale 
barley-malt  are  taken,  sufficient  water  added  to  completely  saturate  it,  and  when  saturated 
to  slightly  cover  it.  When  this  mixture  has  stood  three  or  four  hours,  as  much  of  the  solu- 
tion as  possible  is  pressed  out  by  means  of  a  filter-press.  If  the  liquid  is  not  bright  it  must 
be  filtered.  To  the  clear  bright  solution  rectified  spirit  is  added  as  long  as  a  flocculent 
precipitate  forms,  the  addition  of  the  alcohol  being  discontinued  as  soon  as  the  supernatant 
liquid  becomes  opalescent  or  milky.  The  precipitate  is  washed  with  alcohol  of  0.86  to  0.88 
sp.  gr.,  dehydrated  with  absolute  alcohol,  pressed  between  cloth  to  free  it  as  much  as  possible 
from  that  liquid,  and  dried  in  vacua  over  sulphuric  acid,  until  the  weight  becomes  constant. 

Prepared  in  this  way,  the  substance  is  a  white,  friable,  easily  soluble  powder,  retaining 
its  activity  for  a  considerable  time.  The  preparation  usually  sold  as  diastase  is  useless  for 
this  work. 


422  STARCH   AND    ITS    ISOMERIDES. 

On  keeping  the  liquid  at  62°  to  63°  for  a  short  time,  the  starch  is 
completely  converted  into  maltose  and  dextrin,  and  a  drop  of  the  solu- 
tion no  longer  gives  a  blue  colouration  with  iodine,  but  it  is  desirable 
to  continue  the  treatment  for  about  an  hour  after  the  disappearance 
of  the  starch,  as  the  solution  then  niters  more  readily.  The  liquid  is 
then  heated  to  boiling  for  10  minutes,  and  filtered,  the  residue  being 
carefully  washed  with  small  quantities  of  boiling  water.  The  filtrate 
is  cooled,  and  made  up  to  100  c.c.  and  the  density  observed.  The 
maltose  is  then  determined  by  Fehling's  solution,  and  the  dextrin 
deduced  from  the  rotatory  power  of  the  solution.  The  maltose  found, 
divided  by  1.055,  gives  the  corresponding  weight  of  starch,  which, 
added  to  the  dextrin  found,  gives  the  total  number  of  grm.  of  starch 
represented  by  100  c.c.  of  the  solution.1  The  sum  of  the  dextrin  and 
maltose  found  directly  ought  to  agree  fairly  well  with  the  total  solid 
matter  estimated  from  the  density  of  the  solution,  after  making  allow- 
ance for  the  weight  of  diastase  employed. 

The  A.  O.  A.  C.  modifies  this  method  as  follows: 

Extract  3  grm.  of  the  finely  powdered  substance  on  a  hardened 
filter  with  5  successive  portions  of  10  c.c.  of  ether,  wash  with  150  c.c. 
of  10%  alcohol,  and  then  with  a  little  strong  alcohol.  Place  the 
residue  in  a  beaker  with  50  c.c.  of  water,  immerse  the  beaker  in  a 
boiling  water-bath,  and  stir  the  contents  constantly  for  15  minutes  or 
until  all  of  the  starch  is  gelatinised;  cool  to  55°;  add  from  20  to  40  c.c. 
of  malt  extract  and  maintain  at  this  temperature  until  a  microscopic 
examination  of  the  residue  with  iodine  reveals  no  starch.  Cool  and 
make  up  directly  to  250  c.c.;  filter.  Place  200  c.c.  of  the  filtrate  into  a 
flask  with  20  c.c.  of  25  %  hydrochloric  acid  (sp.  gr.  1.125);  <\on~ 
nect  with  a  reflux  condenser  and  heat  in  a  boiling  water-bath  for  21/2 
hours;  nearly  neutralise  while  hot  with  sodium  carbonate,  and  make 
up  to  500  c.c.  Mix  the  solution  well,  pour  through  a  dry  filter, 
and  determine  the  dextrose  in  an  aliquot  part.  Convert  the  dextrose 
into  starch  by  the  factor  0.90. 

Preparation  of  Malt  Extract. — Digest  10  grm.  of  fresh,  finely- 
ground  malt  2  or  3  hours  at  ordinary  temperature,  with  200  c.c.  of 

JIn  very  accurate  experiments  it  may  be  well  to  estimate  the  a-amylan  present  in  the 
solution.  For  this  purpose,  75  c.c.  of  the  above  solution  should  be  evaporated  to  about 
30  c.c.,  cooled,  and  60  c.c.  of  rectified  spirit  added.  A  few  drops  of  hydrochloric  acid  are 
then  added,  and  the  opalescent  liquid  stirred,  when  a  flocculent  precipitate  will  probably 
be  produced.  This  is  allowed  to  subside  and  the  clear  supernatant  liquid  is  decanted  off. 
The  residue  is  then  washed  with  alcohol  of  0.86  sp.  gr.,  dehydrated  by  treatment  with  strong 
alcohol,  and  collected  on  a  tared  filter.  It  is  then  dried  in  vacua  over  sulphuric  acid,  and 
afterwards  in  dry  air  at  100°  C.,  being  subsequently  weighed. 


STARCH.  423 

water,  and  filter.  Ascertain  the  amount  of  dextrose  in  a  given  quan- 
tity of  the  filtrate  after  boiling  with  acid,  etc.,  as  in  the  starch  determina- 
tion, and  make  the  proper  correction. 

The  methods  of  estimating  starch  have  been  very  fully  investigated 
by  Horace  T.  Brown  (Trans.  Guiness  Research  Lab.,  1903,  I,  79), 
who  has  made  use  of  a  modified  Soxhlet  extractor  to  facilitate  the 
removal  of  the  amylans  in  O'Sullivan's  method. 

An  indirect  method  of  determining  starch  in  barley  may  be  based 
on  the  fact  that,  if  the  products  of  starch  hydrolysis  with  diastase 
are  fermented  with  yeast  in  presence  of  a  small  quantity  of  active  dias- 
tase, the  dextrins  as  well  as  the  maltose  can  be  completely  fermented. 

5  grm.  of  barley  are  extracted  with  ether  and  alcohol  (sp.  gr.  0.90) ; 
the  residue  is  washed  into  a  flask  and  thoroughly  boiled  to  remove 
alcohol  and  to  gelatinise  the  starch  and  converted  with  6  c.c.  of  an 
active  malt  extract  and  fermented  without  previous  destruction  of  the 
diastase  with  i  grm.  of  yeast  at  26-27°,  for  several  days.  The  alcohol 
is  determined  by  the  distillation  method;  a  control  solution  with  yeast, 
malt  extract  and  water  is  kept  under  identical  conditions  and  the  alco- 
hol produced  allowed  for.  92  parts  of  alcohol  represent  153.9  parts 
of  starch. 

Horace  Brown's  rapid  method  enables  the  estimation  of  starch  in 
a  barley  to  be  carried  out  in  5  hours. 

5  grm  of  the  grain  are  extracted  in  a  suitable  apparatus  with 
alcohol  (sp.  gr.  0.90)  for  3  hours,  transferred  to  a  beaker  containing 
100  c.c.  of  water  and  the  whole  thoroughly  boiled  after  cooling  to 
57°,  10  c.c.  of  an  active  malt  extract  are  added  and  the  conversion 
allowed  to  proceed  for  60  minutes.  The  solution  is  boiled,  filtered  into 
a  200  c.c.  flask,  the  residue  well  washed  and  the  volume  adjusted 
after  cooling.  The  cupric  reduction  of  20  c.c.  is  determined  and  the 
maltose  calculated  from  the  copper  reduced  after  the  correction  for 
the  reduction  due  to  the  malt  extract.  84.4  parts  of  maltose  corre- 
spond to  100  parts  of  starch.  The  malt  used  should  have  a  diastatic 
power  of  80  Lintner. 

Marcker  and  Morgen's  method,  much  used  on  the  Continent,  is  as 
follows:  3  grm.  of  finely  divided,  fat  free  substance  are  heated 
in  a  small  metal  vessel  with  50  c.c.  of  water  for  20  minutes  at  100°, 
cooled  to  79°,  and  liquefied  by  means  of  5  c.c.  of  malt  extract  for  20 
minutes.  5  c.c.  of  i  %  tartaric  acid  are  added  and  the  vessel  heated 
in  a  Soxhlet  digester  for  half  an  hour  at  a  pressure  of  3  atmospheres. 


424  STARCH   AND    ITS    ISOMERIDES. 

Following  a  further  addition  of  5  c.c.  of  tartaric  acid,  the  vessel  is 
removed  and  again  heated  for  20  minutes  at  70°.  The  solution  is 
filtered,  diluted  to  200  c.c.  and  inverted  by  boiling  with  15  c.c.  of 
hydrochloric  acid  (sp.  gr.  1.125)  for  3  hours  in  a  flask  attached  to  a 
reflux  condenser.  The  liquid  is  cooled,  neutralised  by  sodium 
hydroxide,  made  up  to  500  c.c.  and  the  sugar  estimated  by  Fehling's 
solution. 

Polarimetric  Estimation  of  Starch  in  Cereals. — C.  J.  Lintner 
(Z.  ges.  Brauw.,  1907,  30,  109)  gives  the  following  method:  5  grm. 
of  the  very  finely  powdered  cereal  are  triturated  in  a  mortar  with 
20  c.c.  of  water  until  no  lumps  remain;  40  c.c.  of  concentrated 
hydrochloric  acid  are  then  added  and  the  mixture  left  for  30  minutes ; 
the  pale  yellow-coloured  paste  will  have  become  darker  and  more  fluid. 
The  liquid  is  then  washed  into  a  measuring  flask  of  200  c.c.  capacity 
by  means  of  hydrochloric  acid  of  sp.  gr.  1.125,  10  c.c.  of  4  % 
solution  of  phosphotungstic  acid  are  added  to  precipitate  the  proteins, 
and  the  volume  made  up  to  200  c.c.  with  the  diluted  hydrochloric  acid. 
The  liquid  is  shaken  and  filtered  and  the  clear  filtrate  examined  by 
the  polarimeter  in  a  2  dcm.  tube.  The  concentration  of  the  soluble 
starch  is  calculated  on  the  basis  of  [a]D=  200.3°  f°r  barley  starch  dis- 
solved in  hydrochloric  acid  at  20°.  Provided  the  liquid  be  not  allowed 
to  remain  longer  than  2  hours  before  polarising,  no  decrease  in  the 
rotatory  power  need  be  feared.  The  method  gives  results  4  to  6% 
lower  than  the  acid  inversion  process,  owing  to  the  pentosans,  etc., 
being  counted  as  starch  in  the  latter  process. 

Canet  and  Durieux  (Bull.  Soc.  Chim.  Belg.,  1907,  21,  329)  find 
Lintner's  method  to  be  generally  applicable.  They  use  Brown's 
figure  [a]D  =  202°  for  the  specific  rotatory  power  of  starch.  Unless 
the  material  is  rich  in  nitrogenous  matter,  it  is  not  necessary  to  add 
phosphotungstic  acid.  The  material  should  be  free  from  fat  and  be 
dried  before  treatment.  A  few  of  the  results  may  be  cited;  they  are 
expressed  as  dry  starch  on  air-dry  material. 

Potato  fecula  84.15;  maize  starch  82.66;  rice  starch  83.06;  corn  flour 
70.04;  rice  flour  76.73;  malt  flour  50.02;  yellow  maize  58.16;  maize 
grits  75.43  ;  bran  23.51;  brewers'  grains  1.73  to  9.10;  maize  press  cake 
8.66. 

Wenglein  (Z.  ges.  Brauw.,  1908,  31,53)  substitutes  sulphuric  acid 
of  sp.  gr.  1.70  for  hydrochloric  acid  in  Lintner's  process  and  washes 
with  acid  of  sp.  gr.  1.30,  but  the  method  is  otherwise  the  same.  The 


STARCH.  425 

solutions  in  sulphuric  acid  can  be  kept  8  hours  unchanged  before  polar- 
ising [<z]D  =  191.7°  for  starch  in  sulphuric-acid  solution. 

The  above  authors  consider  the  optical  activity  of  other  constituents 
in  starch-yielding  cereals  to  be  so  small  as  to  be  negligible.  Ewers 
(Z.  ofjentl.  Chem.,  1908,  14,  8)  disputes  this  and  states  that  a  con- 
trol experiment  to  determine  the  optical  rotation  of  the  soluble  carbo- 
hydrates is  always  necessary.  For  this  control  5  grm.  of  the  substance 
and  70  c.c.  of  water  are  digested  for  i  hour  at  50°,  then  25  c.c.  of  glacial 
acetic  acid  are  added  and  the  digestion  continued  for  half  'an  hour. 
The  filtered  extract  is  made  up  to  volume  and  polarised. 

Gschwendner  (Chem.  Zeit.,  1906,  30,  761)  advises  the  following 
method  for  the  valuation  of  maize  and  cereals:  5  to  7.5  grm.  of  meal 
are  shaken  with  25  to  30  c.c.  of  acidified  brine  (made  by  dissolv- 
ing 100  grm.  of  salt  in  400  c.c.  of  water  and  adding  50  c.c.  of  23% 
hydrochloric  acid)  in  a  flask  attached  to  a  reflux  condenser  and 
heated  in  a  calcium  chloride  bath  for  i  1/4  hours.  The  contents 
are  clarified  with  5  c.c.  basic  lead  acetate,  diluted  to  50  c.c.,  an  excess  of 
water  added  corresponding  to  the  volume  of  the  undissolved  residue 
added,  and  the  filtrate  polarised.  The  rotatory  power  is  calculated 
as  dextrose  and  multiplied  by  0.9  to  give  the  starch. 

Parow  and  Neumann  (Z.  Spiritusind.,  1907,  30,  561)  modify  this 
method  somewhat  and  find  it  gives  satisfactory  results. 

Commercial  Starch. — This  is  usually  obtained  from  wheat,  rice, 
maize  or  potatoes.  In  England  hardly  any  starch  is  now  made  from 
wheat.  Characteristic  of  wheat  starch  is  the  coherence  of  the  granules 
due  to  the  small  admixture  of  gluten.  A  rough  estimation  of  the  starch 
in  wheat  flour  may  be  effected  by  washing  a  weighed  quantity  over  a 
muslin  sieve  in  a  stream  of  water.  The  gluten  remains  and  the  water 
containing  the  starch  is  allowed  to  stand  until  the  starch  has  settled, 
when  it  is  collected,  dried  at  110°  and  weighed. 

The  ash  of  starch  is  trifling  in  amount,  its  estimation  serves  to 
detect  any  mineral  additions. 

The  moisture  may  be  determined  by  drying  in  a  vacuum  over  sul- 
phuric acid  or  in  a  current  of  dry  air  at  100°.  For  approximately 
estimating  the  water  in  potato  starch,  Saare's  method  is  more  con- 
venient. It  consists  in  placing  100  grm.  of  the  sample  in  a  250  c.c. 
flask,  filling  the  flask  to  the  mark  with  water  at  17.5°,  and  observing  the 
weight  of  the  contents.  There  is  no  occasion  to  employ  the  large 
quantities  of  starch  and  water  recommended  by  Saare.  He  gives  a 


426  STARCH   AND    ITS    ISOMERIDES. 

table  (Jour.  Soc.  Chem.  Ind.,  1884,  3,  527)  by  which  the  proportion  of 
water  is  directly  shown,  but  the  following  rule  may  be  employed  in- 
stead :  From  the  weight  of  the  starch  and  water  contained  in  the 
bottle  subtract  250,  and  divide  the  difference  by  0.3987,  when  the  quo- 
tient will  be  the  percentage  of  starch  in  the  sample.  This  instruction 
applies  to  the  quantities  of  starch  and  water  prescribed  by  Saare,  but 
the  following  is  a  more  general  expression  of  the  rule : 

Contents  of  bottle  in  grm.  minus  capacity  of  bottle  in  c.c^  f     ^    of   anhydrous  starch  in 


g  .weight    of  sample  taken. 

The  method  gives  values  within  0.5%  and  an  estimation  can  be 
made  in  30  minutes.  J.  H.  Hoffmann  (Woch.  fur  Brauerei.,  1903, 
No.  31)  heats  the  starchy  matter  to  drive  out  the  water  which 
is  condensed,  collected  and  measured.  50  grm.  of  starch  are  im- 
mersed in  400  c.c.  of  oil  of  turpentine  and  10  c.c.  of  toluene  in  a  boil- 
ing vessel  and  heated  first  at  50°,  then  to  140°  and  finally  to  155° 
for  5  minutes  in  each  case.  The  water  formed  is  collected  and  meas- 
ured, a  correction  of  0.2  c.c.  added  and  the  whole  multiplied  by  2  to 
give  the  percentage  of  water  in  the  starch. 

For  technical  purposes  it  is  sometimes  desired  to  estimate  the  pro- 
portion of  starch  existing  in  potatoes.  This  can  be  done  in  a  rough 
and  ready  manner  by  ascertaining  the  sp.  gr.  of  the  tuber.  The  un- 
peeled  potatoes,  freed  from  dirt,  are  placed  in  a  solution  of  salt,  which 
is  then  diluted  with  water  till  some  of  the  individual  tubers  sink,  while 
others  just  float.  The  density  of  the  saline  solution,  as  ascertained  by 
a  hydrometer,  is  then  equal  to  the  average  sp.  gr.  of  the  potatoes. 
Another  method  consists  in  taking  5  kilogrm.  of  the  potatoes,  and  then 
weighing  in  water.  The  weight  in  water  divided  into  the  original 
weight  in  air  gives  the  sp.  gr.  Tables  have  been  compiled  for  ascer- 
taining the  percentage  of  starch  from  the  sp.  gr.  of  the  potatoes. 

The  sp.  gr.  ranges  from  1.08  to  1.15,  the  heaviest  potatoes  containing 
most  starch  and  most  dry  matter.  The  most  used  tables  are  those  of 
Behrend,  Marcker  and  Morgen  (Zeit.  furSpiritusind.,  1879,361), 
which  give  results  accurate  within  2%.  An  approximate  estima- 
tion may  be  based  on  the  following:  A  potato  containing  19.9% 
of  dry  matter  has  a  sp.  gr.  1.081;  an  increase  of  o.ooi  in  the  sp.  gr. 
corresponds  to  0.214%  of  dry  matter.  The  dry  matter  less  5.75  is 
equal  to  the  weight  of  starch  contained. 

Starches  are  often  graded  according  to  the  stiffness  of  the  pastes 
they  yield  under  comparable  conditions  when  boiled  with  water  and 


DEXTRIN.       AMYLIN.  427 

cooled.  Ermen  (/.  Soc.  Chem.  Ind.,  1907,  26,  501-502)  makes  solu- 
tions of  starch  in  the  cold  with  the  help  of  sodium  hydroxide  and 
determines  their  viscosities  in  a  Redwood  viscometer. 

The  weighed  sample  of  starch  is  shaken  continuously  with  230  c.c. 
of  cold  water  and  15  c.c.  of  a  10%  solution  of  sodium  hydroxide 
with  the  addition  of  enough  water  to  bring  the  whole  up  to  250  c.c. 
until  the  solution  begins  to  thicken.  It  is  allowed  to  stand  until 
the  next  morning  before  measurement.  When  close  attention  is  paid 
to  constancy  of  procedure,  the  method  is  claimed  to  give  concordant 
results  with  the  same  starch  whilst  different  starches  and  different 
brands  of  the  same  starch  are  easily  differentiated. 

DEXTRIN.     AMYLIN. 

Dextrin  is  a  product  obtained  by  treating  potato,  wheat  or  maize 
starch  or  other  amylaceous  bodies  in  certain  ways.  The  following 
modes  of  treatment  cause  a  formation  of  dextrin: 

By  heating  starch  or  flour  at  a  temperature  ranging  from  210° 
to  280°  until  it  acquires  a  yellow  or  brownish  colour.  The  change  is 
greatly  facilitated  by  moistening  the  starch  with  dilute  nitric  or  other 
acids,  and  then  slowly  drying  the  paste  and  heating  it  for  some  time  to 
about  110°  to  150°. 

By  boiling  starch  with  dilute  sulphuric  acid  till  the  cooled  liquid 
no  longer  gives  any  colouration  with  solution  of  iodine. 

By  treating  gelatinised  starch  with  warm  water  and  a  small  quan- 
tity of  malt  extract. 

The  first  process  is  employed  for  the  manufacture  of  solid  dextrin, 
which  is  known  in  commerce  by  the  name  of  British  gum,  gommeline, 
starch-gum,  etc.  The  other  processes  result  in  a  simultaneous  forma- 
tion of  maltose,  as  described  elsewhere.  The  former  is  used  for  the 
preparation  of  commercial  glucose,  and  the  latter  reaction  takes  place 
in  mashing  malt  for  the  manufacture  of  beer. 

Several,  and  not  impossibly  many,  varieties  of  dextrin  exist,  all  being 
apparently  formed  by  the  breaking  up  of  the  highly  complex  starch 
molecule  by  treatment  with  dilute  acids  or  ferments.  There  is  no 
ready  method  of  distinguishing  the  different  varieties  with  certainty, 
except  that  one  kind,  or  possibly  class,  of  dextrin  gives  a  reddish-brown 
colour  with  solution  of  iodine,  while  the  other  kind  or  class  produces 
no  colouration.  The  erythrodextrin,  the  kind  giving  the  brown  colour 


428  STARCH   AND    ITS    ISOMERIDES. 

with  iodine,  is  an  intermediate  product  of  the  formation  of  achro- 
dextrin  from  starch. 

The  best  method  of  applying  the  iodine  reaction  as  a  test  for  erythro- 
dextrin  is  to  divide  a  very  weak  solution  of  the  iodine  in  potassium  iodide 
into  two  parts,  and  place  the  slightly  yellow  liquid  in  adjacent 
test-tubes  or  glass  cylinders.  On  then  adding  the  solution  to  be 
tested  to  one,  and  an  equal  measure  of  water  to  the  other,  any  brownish 
colouration  will  be  readily  observed.  In  presence  of  starch,  the  blue 
is  apt  to  obscure  the  brown  tint  produced  by  the  erythrodextrin. 
This  may  be  avoided  to  some  extent  by  employing  the  iodine  solution 
somewhat  in  excess,  so  as  to  get  a  full  development  of  the  brown. 

Pure  dextrin  is  a  white  amorphous  solid.  It  is  tasteless,  odourless, 
non-volatile  and  very  deliquescent.  It  dissolves  in  an  equal  weight  of 
cold  water  to  form  a  syrupy,  dextro-rotatory,  liquid,  [a]D  =200°,  which 
is  miscible  with  1.5  measures  of  proof  spirit.  By  strong  spirit,  if 
used  in  sufficient  quantity,  dextrin  is  completely  separated  from  its 
aqueous  solutions. 

Cold  concentrated  sulphuric  acid  dissolves  dry  dextrin  without 
colour,  but  charring  takes  place  on  warming.  By  boiling  with  dilute 
acids,  dextrin  yields  maltose  and  ultimately  dextrose.  Hot  nitric 
acid  of  1.35  sp.  gr.  converts  dextrin  in  part  into  oxalic  acid,  whereas 
the  natural  gums  yield  mucic  acid  under  similar  conditions. 

Dextrin  is  distinguished  from  starch  by  its  solubility  in  cold  water; 
from  soluble  starch  by  yielding  no  blue  with  iodine  when  tested 
as  described  on  page  419,  and  no  precipitate  with  baryta  water;  from 
maltose  and  dextrose  by  not  reducing  Fehling's  solution;  from  starch, 
soluble  starch,  gelatin  and  egg-albumin  by  not  yielding  a  precipitate 
with  tannin;  from  albumin  by  not  being  coagulated  by  heat  or  mineral 
acid. 

Dextrin  is  separated  from  starch  and  cellulose  by  solution  in  cold 
water;  coagulable  proteins  may  then  be  separated  by  raising  the 
faintly  acid  solution  to  boiling.  An  ammoniacal  solution  of  lead  ace- 
tate added  to  the  cold  and  dilute  liquid  is  stated  to  precipitate  the  dex- 
trin, leaving  the  sugar  in  solution.  The  precipitate  may  be  dried  at 
100°,  and  is  said  to  have  the  formula  PbO,C6HIOO5.  Another  method 
consists  in  precipitating  the  dextrin  by  means  of  a  large  proportion  of 
alcohol,  washing  the  precipitate  with  rectified  spirit,  and  drying  it  at 
1 10°.  After  weighing,  the  dextrin  should  be  ignited,  and  the  resultant 
ash  deducted  from  the  total  weight  obtained. 


CELLULOSE.  429 

The  proportion  of  dextrin  present  in  a  solution  also  containing  mal- 
tose and  dextrose  may  be  determined  by  observing  the  rotatory  action 
of  the  liquid,  together  with  its  sp.  gr.  and  reducing  action  on  Fehling's 
solution. 

Commercial  Dextrin. — Commercial  dextrin,  or  "British  gum," 
is  now  manufactured  extensively  by  moistening  starch  or  flour  with  a 
mixture  of  dilute  nitric  and  hydrochloric  acids,  and  then  exposing  it  to 
a  temperature  of  100°  to  125°.  Either  nitric  or  hydrochloric  acid  singly 
may  be  substituted  for  the  mixture  or  oxalic  acid  may  be  employed. 

Commercial  dextrin  is  a  white,  yellowish  or  light  brown  powder. 
It  consists  largely  of  erythrodextrin,  and  hence  its  aqueous  solution 
is  coloured  brown  with  iodine,  unless  this  reaction  is  obscured  by  the 
blue  produced  by  a  considerable  proportion  of  soluble  starch.  For 
most  purposes  this  admixture  is  unobjectionable,  provided  that  it 
does  not  exceed  12  or  15  %.  Unaltered  starch  may  be  recognised 
by  the  microscope  and  its  insolubility  in  cold  water.  Reducing  sugars 
(maltose)  are  nearly  always  present  in  commercial  dextrin,  and  may 
be  detected  and  estimated  by  Fehling's  solution. 

.  Many  mixtures  of  starch  and  dextrin  are  employed  as  thickening 
agents  in  calico-printing,  etc.  "Gloy"  consists  essentially  of  farina 
mixed  with  a  solution  of  magnesium  chloride. 

Dextrin  syrups  are  largely  employed  by  confectioners.  Their  ex- 
amination is  described  under  "glucose." 

The  method  of  distinguishing  commercial  dextrin  from  gum  arabic 
is  described  on  page  442. 

CELLULOSE,1   C6H10OS. 

Cellulose  constitutes  the  essential  part  of  the  solid  frame-work  or 
cellular  tissue  of  plants  and  is  an  especially  characteristic  product  of 
the  vegetable  kingdom.  Tunicin,  a  compound  resembling  cotton 
cellulose  in  many  ways,  is  obtained  from  the  outer  coating  of 
Ascidia  and  other  invertebrate  species. 

Cellulose  occurs  nearly  pure  in  cotton,  linen  and  the  pith  of  certain 
plants.  Still  purer  forms  are  Swedish  filter-paper,  linen  rags  and  cotton 
wool.  Cellulose  is  more  stable  than  starch.  It  is  insoluble  in  water 
and  all  simple  solvents.  Air-dry  cellulose  contains  from  6  to  12% 

1  For  full  information  on  the  subject  of  cellulose  the  work  of  Cross  and  Be  van  on  Cellulose 
should  be  consulted,  also  "Researches  on  Cellulose,"  1895-1900,  1900-1905. 


430  STARCH   AND    ITS    ISOMERIDES. 

of  water  which  is  readily  driven  off  at  100°,  but  reabsorbed  on 
exposure  to  the  atmosphere,  and  is  termed  "moisture  of  condition." 
This  moisture  is  of  much  importance  in  the  processes  of  spinning  and 
finishing  fibres  and  also  in  the  buying  and  selling  of  fibrous  products. 

Cellulose  hydrates  give  an  indigo-blue  colouration  with  iodine  in 
aqueous  solution.  They  do  not,  however,  differ  in  their  essential 
properties  from  cellulose. 

The  water  of  hydration  of  a  cellulose  may  be  determined  as  the 
difference  between  the  hygroscopic  moisture  lost  at  100-105°,  an^ 
that  which  is  driven  off  at  the  temperature  of  boiling  toluene.  The 
sample  is  boiled  with  toluene  and  the  water  which  distils  over  is 
absorbed  by  calcium  chloride  and  weighed  after  removal  of  the  hydro- 
carbon. 

To  determine  the  degree  of  hydration  of  a  cellulose,  the  sample  is 
stained  blue  with  zinc  chloride-iodide  reagent  and  the  rapidity  with 
which  the  colour  is  removed  by  water  is  noted.  Highly  hydrated 
celluloses  retain  the  colour  for  a  considerable  time. 

Solvents  of  Cellulose. — i.  Aqueous  zinc  chloride:  4  to  5  parts 
of  zinc  chloride  are  dissolved  in  5  to  7  parts  of  water  and  i  part  of, 
cotton  cellulose  stirred  in  till  evenly  moistened,  the  solution  being 
heated  in  a  porcelain  dish  over  the  water-bath.  It  is  stirred  from  time 
to  time  and  water  added  to  replace  that  which  evaporates.  The 
solution  forms  a  precipitate  of  cellulose  hydrate  containing  zinc  salt 
on  pouring  into  water  or  alcohol.  Digestion  with  dilute  hydrochloric 
acid  removes  the  zinc  salt.  This  solution  is  employed  for  making 
cellulose  threads  which  are  carbonised  for  use  in  the  incandescent 
electric  lamp.  Zinc  chloride  dissolved  in  twice  its  weight  of  40% 
aqueous  hydrochloric  acid  dissolves  cellulose  rapidly  in  the  cold, 
but  the  cellulose  undergoes  a  gradual  hydrolysis. 

2.  Ammoniacal  cupric  oxide  (Schweitzer's  reagent)  contains  10  to 
15%  ammonium  hydroxide  and  2  to  2.5%  copper-as  CuO.  It  is 
prepared  either  by  adding  ammonium  chloride  and  an  excess  of 
sodium  hydroxide  to  a  solution  of  cupric  salt  and  redissolving  the 
well-washed  blue  precipitate  in  ammonia  (0.92  sp.  gr.)  or  by  im- 
mersing copper  turnings  in  strong  ammonia  in  a  cylinder  and  bub- 
bling air  or  oxygen  through  the  liquid  for  about  6  hours.  On  treat- 
ment with  the  cuprammonium  solution,  cellulose  becomes  gelatinous 
and  on  agitation  gradually  dissolves  forming  a  viscid  solution  which 
may  be  filtered  after  dilution  with  water. 


CELLULOSE.  431 

On  neutralising  the  filtrate  with  hydrochloric  acid  the  cellulose  is 
separated  in  a  flocculent  state  resembling  aluminum  hydroxide,  which 
when  dried  forms  a  brittle,  greyish,  horn-like  mass.  Carbon  dioxide 
also  precipitates  the  solution,  as  do  sugar,  salt  and  even  copious  dilu- 
tion with  water. 

The  solution  of  cellulose  in  Schweitzer's  reagent  is  decomposed 
by  dialysis.  It  is  laevorotatory,  a  i%  solution  showing  a  specific 
rotation  of  — 20°  for  the  light  transmitted,  which  bears  to  the  sodium 
ray  the  ratio  1:1.85.  The  optical  activity  is  not  strictly  proportional 
to  the  cellulose  dissolved,  increasing  somewhat  more  slowly  than  the 
concentration  of  the  solution. 

Fabrics  passed  through  a  bath  of  the  reagent  are  surfaced  by  the 
film  of  gelatinised  cellulose  and  compacted  together  so  that  the  fab- 
ric becomes  waterproof.  The  cellulose  retains  the  copper  hydroxide 
which  acts  as  a  preservative. 

On  prolonged  boiling  with  dilute  acids,  cellulose  is  converted  into 
hydrocellulose  which  differs  from  cellulose  in  containing  free  carbonyl 
groups  and  in  the  greater  reactivity  of  its  hydroxyl  groups.  Cold  con- 
centrated sulphuric  acid  rapidly  attacks  and  dissolves  cellulose  with  the 
formation  of  dextrin-like  bodies.  If  the  solution  be  now  diluted  a'nd 
boiled,  dextrose  is  formed  as  the  chief  product  of  hydrolysis.  Hot 
concentrated  sulphuric  acid  at  once  chars  cellulose.  On  treatment  with 
sulphuric  acid  diluted  with  half  its  volume  pf  water  (sp.  gr.  1.5  to  1.6) 
cellulose  is  gelatinised  and  converted  into  a  substance  termed  amyloid, 
which  is  coloured  blue  by  iodine.  Paper  placed  in  an  acid  of  this 
strength  for  a  short  time  and  then  transferred  to  water  has  a  tough 
coating  of  amyloid  fixed  on  its  surface  and  constitutes  parchment 
paper. 

By  treatment  with  cold  nitric  acid  of  1.42  sp.  gr.  cellulose  is  remark- 
ably toughened,  without  losing  its  fibrous  structure  or  becoming  ni- 
trated. With  stronger  acid,  cellulose  is  converted  into  nitro-substitu- 
tion  products  which  are  described  elsewhere. 

Nitric  acid  (sp.  gr.  i.i  to  1.3)  oxidises  cellulose  to  oxycellulose ; 
dilute  chromic  acid  has  a  similar  effect.  Hypochlorites  in  dilute  solu- 
tion (i%)  have  only  a  very  slight  action  on  cellulose  proper.  Per- 
manganates in  neutral  solution  also  attack  cellulose,  but  slowly.  In 
stronger  solutions,  the  fibre  substance  is  oxidised  and  disintegrated 
and  an  oxycellulose  results.  The  joint  action  of  hypochlorite  solutions 
and  carbonic  acid  rapidly  produce  oxycellulose,  which  acquires 


432  STARCH   AND    ITS    ISOMERIDES. 

the  property  of  selective  attraction  for  certain  colouring  matters — 
notably  the  basic  coal-tar  dyes.  Oxycelluloses  in  overbleached  cloth 
may  thus  be  easily  detected  by  immersion  of  the  fabric  in  a  dilute  solu- 
tion of  methylene  blue. 

Cellulose  is  very  resistant  to  dilute  alkaline  solutions  even  at  high 
temperatures.  Cellulose  fibres  are  freed  by  drastic  treatment  with  i  to 
2  %  sodium  hydroxide  from  non-cellulose  constituents  which  become 
saponified.  Cold  solutions  containing  above  13%  sodium  hydroxide 
cause  a  remarkable  change  in  the  structure  of  the  fibre  which,  seen  in 
the  mass,  causes  a  shrinkage  in  length  and  width  with  an  increase 
in  thickness.  The  compound  of  cellulose  and  alkali  formed  is  de- 
composed on  washing  with  water,  the  cellulose  reappearing  as  the 
hydrate  CI2H20OI0.  This  is  known  as  mercerised  cellulose. 

This  alkali-cellulose  reacts  with  carbon  disulphide  forming  an 
alkali-cellulose-xanthate  which  is  perfectly  soluble  in  water,  giving 
a  very  viscous  solution  which  is  precipitated  in  the  form  of  a  gelat- 
inous hydrate  by  various  neutral  dehydrating  liquids  or  solutions. 
To  prepare  it,  cellulose  is  treated  with  excess  of  15%  solution  ol 
sodium  hydroxide  and  after  standing  for  some  time  separated  from 
the  liquid,  squeezed  to  remove  excess  and  mixed  with  40  to  100  parts 
of  carbon  disulphide.  After  some  hours,  the  yellowish  mass  is  covered 
with  water  and  subsequently  stirred  with  more  water  when  solution 
occurs. 

Cellulose  is  regenerated  from  this  solution  on  standing  some  days  or 
on  heating  at  80  to  90°.  It  has  3  to  4%  more  moisture  and  cor- 
responds to  the  formula  4C6HIOO5.H2O.  In  general  it  is  far  more 
reactive  than  the  original  cellulose. 

If  cotton-wool  or  filter-paper  be  heated  at  180°  for  several  hours 
with  about  6  or  8  parts  of  acetic  anhydride,  it  is  entirely  dissolved 
and  converted  into  a  triacetate,  C6H7(C2H3O)3OS,  which  may  be  sepa- 
rated by  pouring  the  syrup  into  water;  it  is  a  white  powder,  optically 
inactive,  soluble  in  strong  acetic  or  sulphuric  acid,  and  very  readily 
converted  into  cellulose  and  potassium  acetate  by  boiling  with  dilute 
caustic  potash.  Other  acetyl-derivatives  of  cellulose  have  been 
obtained. 

The  estimation  of  the  cupric  reducing  power  is  said  to  afford 
a  useful  measure  of  the  free  carbonyl  groups  in  cellulose  and  hence 
of  the  chemical  condition  of  the  sample.  Schwalbe  (Ber.,  1907,  40, 
1347  to  1351)  determines  this  in  the  following  manner: 


CELLULOSE.  433 

Two  portions,  of  about  3  grm.  each,  of  the  cellulose  are  weighed 
out;  one  portion  serves  for  the  determination  of  the  absolute  dry 
substance,  whilst  the  other  is  reduced  to  a  fine  state  of  division,  without 
drying  by  heat,  and  is  mixed  with  200  c.c.  of  water  and  100  c.c.  of 
Fehling's  solution.  The  liquid  is  boiled  for  15  minutes  under  a 
reflux  condenser,  with  frequent  agitation.  The  liquid  is  then  filtered 
hot  and  the  residue  containing  the  cuprous  oxide  is  then  dissolved 
in  nitric  acid  and  the  amount  of  copper  determined,  preferably  by  the 
electrolytic  method.  The  "copper  value"  represents  the  percentage 
of  metallic  copper  calculated  on  the  dry  cellulose.  Cotton  wool  has  a 
value  about  1.7,  bleached  sulphite  wood  pulp  about  3.9,  overbleached 
sulphite  wood  pulp  19.3. 

In  a  second  paper  (Ber.,  1907,  40,  4523-4527)  Schwalbe  applies  the 
test  to  artificial  silks.  Viscose  and  Pauly  silks,  both  made  by  alkali 
processes,  have  low  copper  values,  about  0.8.  Chardonnet  silk,  being 
made  by  an  acid  process,  has  a  value  of  3.1. 

Hydrocelluloses  show  values  of  2  to  8.8  according  to  the  degree 
of  hydrolysis.  Oxycelluloses  have  much  higher  copper  values,  7.6 

to  35- 
Plant  celluloses  may  be  classified  in  3  groups  (Cross  and  Bevan): 

1.  Those  of  maximum  resistance  to  hydrolysis  which  contain  no 
carbonyl  groups — normal  cellulose. 

2.  Those  of  less  resistance  to  hydrolysis  and  containing  active  car- 
bonyl groups — the  oxycelluloses. 

3.  Those  easily  hydrolysed  by  acid  or  in  some  cases  by  enzymes 
to  form  simple  carbohydrates  and  which  are  more  or  less  soluble 
in  alkaline  solutions — the  pseudo-  or  hemi-celluloses. 

To  establish  the  nature  of  a  cellulose,  it  is  generally  sufficient 
to  determine  the  ultimate  composition,  resistance  to  alkaline  hydrol- 
ysis, behaviour  with  solvents,  reaction  with  sulphuric  acid  (solution 
without  blackening)  and  with  a  nitrating  mixture  (nitric  acid  and 
sulphuric  acid). 

Materials  composed  of  normal  and  resistant  celluloses  only  are 
quite  inert  and  have  lasting  properties.  Those  containing  oxidised 
and  oxycelluloses,  also  lignocelluloses,  are  liable  to  discolouration 
and  are  far  more  perishable. 

The  lignocelluloses,  of  which  the  jute  fibre  is  a  typical  representative, 

f^TT 

differ  markedly  from  the  celluloses.     They  have  a  higher  -    -  ratio, 
VOL.  1—28 


434  STARCH    AND    ITS    ISOMERIDES. 

contain  unsaturated  groups  which  combine  with  chlorine  to  form 
quinone  bodies.  They  contain  a  furfural  yielding  complex,  methoxyl 
groups  and  an  acetic  acid  residue.  These  constituents  make  up  the 
non-cellulose  part  of  the  fibre  often  termed  lignin,  in  addition  to  which 
it  contains  cellulose  proper  which  can  only  be  isolated  after  the  chemi- 
cal decomposition  of  the  non-cellulose. 

Lignocelluloses  possess  a  number  of  characteristic  reactions.  Salts 
of  aniline  colour  the  fibre  a  deep  golden-yellow.  Phloroglucinol,  dis- 
solved in  hydrochloric  acid,  gives  a  deep  magenta  colouration.  Iodine 
is  absorbed  in  large  quantity,  colouring  the  fibre  a  deep  brown.  The 
fibre  readily  combines  with  chlorine,  as  shown  by  the  characteristic 
magenta  colouration  developed  on  the  subsequent  addition  of  sodium 
sulphite.  Very  characteristic  is  the  reaction  with  ferric  ferricyanide 
obtained  by  mixing  equivalent  proportions  of  potassium  ferricyanide 
and  ferric  chloride.  The  fibre  stains  a  deep  blue  and  takes  up  a 
considerable  quantity  of  pigment. 

Pectocelluloses. — These  contain  a  larger  proportion  of  oxygen 
than  the  celluloses  and  give  a  series  of  pectic  acids  and  insoluble 
cellulose  on  hydrolysis  with  dilute  alkaline  solutions;  they  are  satu- 
rated compounds. 

Pectose  occurs  in  the  utricular  tissue  of  fruits  and  roots.  It  is 
insoluble  in  water,  but  is  converted  into  soluble  pectin  on  hydrolysis 
with  dilute  acids  or  alkalies  or  by  an  enzyme,  pectase.  In  addition 
to  the  pectocelluloses  proper,  as  typified  by  flax,  esparto,  etc.,  are  the 
mncocelluloses;  these  are  decomposed  by  the  action  of  water,  forming 
the  solutions  known  as  mucilages,  which  are  neutral  and  on  ultimate 
hydrolysis  give  rise  to  the  formation  of  various  hexoses  and  pentoses. 

The  cutocelluloses  are  associated  with  oily  and  waxy  products 
which  add  to  their  water-resisting  property,  but  are  removed  by  sol- 
vents. On  decomposition  by  oxidation  and  saponification,  a  large 
additional  quantity  of  such  products  is  formed. 

Cutose,  or  cuticular  substance,  constitutes  the  greater  part  of  cork, 
and  the  fine  transparent  membrane  covering  the  exposed  parts  of 
vegetables.  It  contains  a  high  percentage  of  carbon  (0  =  68.29; 
11  =  8.95),  and  yields  suberic  acid,  C8H14O4,  on  oxidation  with  nitric 
acid  of  1.20  sp.  gr.  Cutose  is  insoluble  in  cold  sulphuric  acid  of  1.78 
sp.  gr.  and  in  the  cuprammonium  solution  which  dissolves  cellulose. 
On  the  other  hand,  it  dissolves  slowly  in  a  hot  dilute  solution  of  so- 
dium hyoxide  or  carbonate,  forming  a  solution  from  which  acids 


CELLULOSE.  435 

precipitate  a  yellowish,  flocculent  substance,  fusible  below  100°,  soluble 
in  alcohol  and  ether,  and  having  the  same  composition  as  cutose. 
If  the  alkaline  solution  be  saturated  with  common  salt,  a  cutose-soap 
rises  to  the  surface.  From  the  researches  of  Urbain,  cutose  appears 
to  be  composed  of  stearocutic  acid,  C28H48O4,  with  5  equivalents  of  oleo- 
cutic  acid,  C14H20O4. 

Purification  of  Cellulose  in  the  Laboratory.1—:.  The  fibre 
is  first  subjected  to  alkaline  hydrolysis,  i.  e.,  boiling  with  dilute  sodium 
hydroxide,  carbonate  or  sulphite. 

2.  It  is  then  exposed  to  cMorine  gas  or  bromine  water  or  oxidised 
by  means  of  hypochlorites  or  permanganates.     The  use  of  the  last 
necessitates   treatment  with  sulphurous  acid  to  remove  manganese 
dioxide  deposited  on  the  fibre. 

3.  Finally  process  i  is  repeated  to  remove  products  rendered  soluble 
by  process  2. 

In  consequence  of  its  occurrence  in  association  with  bodies  of  a 
closely  allied  nature,  the  accurate  determination  of  cellulose  is  often  a 
tedious  operation,  and  sortie,  at  least,  of  the  processes  prescribed  for 
the  purpose  yield  arbitrary  rather  than  accurate  results. 

From  starch  cellulose  is  best  separated  by  boiling  the  substance  with 
water  containing  i%  by  volume  of  sulphuric  acid.  The  liqujd  is 
filtered  when  a  drop  taken  out  gives  no  colouration  with  iodine  so 
lution.  In  cases  in  which  the  use  of  acid  is  objectionable,  the  sub- 
substance  should  be  boiled  with  water,  and  the  unfiltered  liquid 
mixed  with  an  equal  measure  of  cold  infusion  of  malt.  The  starch 
will  be  wholly  dissolved  by  keeping  the  liquid  at  a  temperature  of  60° 
for  a  short  time.  The  separation  of  cellulose  from  sugar,  dextrin  and 
other  substances  soluble  in  water  presents  no  difficulty.  Proteins  may 
be  separated  by  treatment  with  warm  water  containing  i%  of  alkali. 
They  may  be  determined  by  the  methods  for  nitrogen. 

For  the  estimation  of  cellulose  in  wood,  vegetable  fibres  and  sub- 
stances to  be  used  for  the  manufacture  of  paper,  Miiller  recommends 
the  following  process:  5  grm.  of  the  finely-divided  substance  are 
boiled  4  or  5  times  with  water,  using  100  c.c.  each  time.  The  residue 
is  dried  at  100°,  weighed,  and  exhausted  with  a  mixture  of  equal 
measures  of  benzene  and  strong  alcohol,  to  remove  fat,  wax,  resin,  etc. 
The  residue  is  again  dried,  and  boiled  several  times  with  water  to  every 

*In  estimating  fibrous  precipitates  it  is  often  advisable  to  collect  on  an  asbestos  filter,  dry 
at  110°  and  weigh,  after  which  the  filter  and  its  contents  are  ignited  and  again  weighed. 
The  loss  in  weight  gives  the  amount  of  precipitate. 


STARCH   AND    ITS    ISOMERIDES. 

ioo  c.c.  of  which  i  c.c.  of  strong  ammonia  has  been  added.  This 
treatment  removes  colouring  matter  and  pectous  substances.  The 
residue  is  further  bruised  in  a  mortar,  if  necessary,  and  is  then  treated 
in  a  closed  bottle  with  250  c.c.  of  water  and  20  c.c.  of  bromine  water 
containing  4  c.c.  of  bromine  in  1000  c.c.  In  the  case  of  the  purer 
bark-fibres,  such  as  flax  and  hemp,  the  yellow  colour  of  the  liquid 
only  slowly  disappears,  but  with  straw  and  woods  decolourisation  oc- 
curs in  a  few  minutes.  When  this  takes  place,  more  bromine  water  is 
added,  and  this  repeated  till  the  yellow  colour  remains  and  bromine 
can  be  detected  in  the  liquid  after  twelve  hours.  The  liquid  is  then 
filtered,  and  the  residue  washed  with  water  and  heated  to  boiling  with 
1000  c.c.  of  water  containing  5  c.c.  of  strong  ammonia.  The 
liquid  and  tissue  are  usually  coloured  brown  by  this  treatment. 
The  undissolved  matter  is  filtered  off,  washed,  and  again  treated  with 
bromine  water.  When  the  action  seems  complete,  the  residue  is 
again  heated  with  ammoniacal  water.  This  second  treatment  is  suf- 
cient  with  the  purer  fibres,  but  the  operation  must  be  repeated  as 
often  as  the  residue  imparts  a  brownish  tint  to  the  alkaline  liquid. 
The  cellulose  is  thus  obtained  as  a  pure  white  substance.  It  is 
washed  with  water,  and  then  with  boiling  alcohol,  after  which  treat- 
ment it  may  be  dried  at  100°  and  weighed. 

Maximum  yields  of  cellulose  are  obtained  by  the  chlorination  proc- 
ess (Cross  and  Bevan,  Trans.  Chem.  Soc.,  1889,  55,  199):  5  grm. 
of  the  fibre  dried  at  100°  are  boiled  for  30  minutes  with  i%  so- 
dium hydroxide,  well  washed  on  a  gauze  filter,  squeezed  to  remove 
excess  of  water  and  placed  in  a  beaker  into  which  a  slow  stream  of 
washed  chlorine  gas  is  passed.  The  fibre  changes  in  colour  from 
brown  to  golden-yellow;  after  30  to  60  minutes'  exposure  it  is  re- 
moved, washed  and  heated  in  a  2%  solution  of  sodium  sulphite  to 
boiling  when  0.2%  sodium  hydroxide  is  added  and  boiling  con- 
tinued for  5  minutes.  The  cellulose  is  then  filtered  and  washed  and 
is  almost  white;  it  may  be  finally  bleached  by  immersion  in  dilute 
hypochlorite  or  permanganate  solution  (0.1%).  The  amount  of 
cellulose  is  2  to  5%  higher  than  that  yielded  by  Mliller's  process  and 
the  method  far  less  tedious. 

Other  methods  involve  the  prolonged  digestion  with  nitric  acid  and 
potassium  chlorate  or  with  dilute  nitric  acid  at  50  to  80°,  but  are  of 
subordinate  interest. 

Lignocelluloses  give  a  blood-red  tint  with   a  reagent  prepared  by 


CELLULOSE.  437 

dissolving  2  grm.  of  paramtraniline  in  100  c.c.  of  hydrochloric  acid 
(sp.  gr.  i. 06)  especially  on  heating. 

The  amount  of  furfural  yielded  by  fibres  on  boiling  with  hydrochloric 
acid  is  estimated  by  Tollens'  method  as  described  under  Pentoses. 

Methoxyl  is  estimated  by  boiling  the  fibre  substance  with  concen- 
trated hydriodic  acid  (ZeiseVs  method). 

To  determine  cellulose,  lignin  and  cutin  in  crude  fibre,  Konig  (Z. 
Untcrs.  Nahr.  u.Genussm.,  1906,  12,  385-395)  digests  the  fibre  in  the 
cold  with  hydrogen  peroxide  in  presence  of  ammonium  hydroxide, 
the  treatment  being  continued  for  a  long  time  with  successive  additions 
of  hydrogen  dioxide  until  the  residue  is  colourless.  The  treatment  oxi- 
dises the  lignin  and  converts  it  into  soluble  products.  The  residue, 
consisting  of  cellulose  and  cutin,  is  treated  with  the  cuprammonium 
solvent  to  dissolve  the  cellulose,  the  cutin  remaining  unattacked. 
The  liquid  is  filtered  on  a  gooch  asbestos  filter  and  the  cutin  residue 
weighed,  the  cellulose  is  precipitated  by  alcohol  and  weighed  and 
the  weight  of  crude  fibre  less  the  weight  of  these  two  is  taken  as 
lignin. 

Konig  states  from  the  investigations  of  hay  and  bran  that  lignin 
contains  55.3  to  59.0%  of  carbon  and  cutin  60  to  75.4%  of  carbon. 
Cellulose  from  the  same  source  contains  methoxyl  groups  varying  in 
proportion  from  0.4  to  2.82%.  Similar  methoxyl  groups  were  un- 
found  by  Cross,  Bevan  and  Beadle  in  the  cellulose  from  jute.  The 
lignin  contains  not  only  methoxyl  groups,  but  also  ethoxyl  and  acetyl 
residues. 

Estimation  of  Crude  Fibre. — In  valuing  food  stuffs  a  distinction 
is  made  between  the  digestible  and  indigestible  constituents.  As  the 
process  of  animal  digestion  is  in  reality  an  exhaustive  series  of  alter- 
nately acid  and  alkaline  hydrolyses,  a  standard  method  of  estimating 
the  crude  fibre  has  been  adopted,  consisting  in  boiling  the  material 
first  with  sulphuric  acid  and  then  with  sodium  hydroxide.  For  the 
A.  O.  A.  C.  process  see  page  70. 

Agar-Agar 

Agar,  often  called  Japanese  isinglass,  is  a  colloid  substance 
prepared  from  marine  algae.  It  consists  of  a  carbohydrate,  sometimes 
called  gelose,  which  is  a  polymer  of  galactose  and  is  converted  into 
galactose  on  boiling  with  dilute  mineral  acids.  Tollens  uses  the  more 
correct  term  J-galactan  for  gelose.  It  has  the  formula  (C6H10O5,)n  is 
kevorotatory  at  first  in  warm  aqueous  solution,  but  changes  to  dextro- 


STARCH   AND    ITS    ISOMERIDES. 

rotatory  on  prolonged  warming.  Agar  also  yields  a  small  proportion 
of  pentoses  when  hydrolysed. 

It  occurs  in  transparent  strips  of  the  thickness  of  a  straw  or  in  shorter 
and  thicker  yellowish  white  pieces.  It  is  odourless  and  tasteless, 
insoluble  in  cold  water,  soluble  in  hot  water.  On  cooling,  the  solution 
gelatinises  to  a  thick  jelly  that  does  not  melt  as  readily  as  that  from 
gelatin.  The  solution  in  500  parts  of  water  still  gelatinises  when  cold. 
It  is  chiefly  employed  as  a  culture  medium  for  bacteria  and  also  used 
as  a  thickening  agent  in  milk  and  cream  and  as  a  substitute  for  white 
of  egg. 

The  aqueous  solution  should  give  no  precipitate  with  tannic  acid 
solution,  proving  the  absence  of  gelatin,  and  no  blue  colouration  with 
iodine,  proving  the  absence  of  starch. 

Commercial  agar  usually  contains  diatoms,  a  characteristic  form 
being  Arachnoidiscus  Ehrenbergii  (see  Fig.  71).  To  obtain  the  diatoms, 
the  organic  material  is  oxidised  with  a  mixture  of  nitric  and  sulphuric 
acids. 


o 


FIG.  71. — Arachnoidiscus  Ehrenbergii.      X  100.     The  smaller  oval  diatoms 
are  a  species  of  Cocconeis.     (Leffmann.) 

Agar  is  much  used  for  thickening  cheap  ice-cream,  especially  that 
sold  in  American  cities  under  the  name  "Hokey-Pokey."  It  is  adapted 
for  such  use  because  its  jelly  does  not  liquefy  at  so  low  a  temperature 
as  that  made  with  gelatin.  Agar  has  also  been  offered  as  a  substitute 
for  gelatin  in  ordinary  diet  because,  being  practically  indigestible  and 
not  irritating,  it  is  supposed  to  give  a  bulkiness  to  the  contents  of 
the  intestine  and  promote  the  peristaltic  movements. 

GUMS. 

Gums  are  a  peculiar  class  of  bodies  occurring  in  the  juices  of  plants. 
They  are  perfectly  non-volatile,  have  little  or  no  taste,  are  uncrystal- 
lisable,  and  eminently  colloidal.  These  characters  render  their  puri- 


GUMS.  439 

fication  very  difficult,  and  hence  but  little  s  known  of  their  chemical 
relationships.  For  convenience,  various  pectous  bodies  are  classed 
with  the  gums. 

The  analytical  characters  of  the  gums  as  a  class  are  indicated  by  the 
following  facts,  which  are  also  applied  to  their  separation  from  similar 
bodies. 

Gums  are  either  soluble  in,  or  swell  up  in  contact  with,  cold  water, 
a  character  which  distinguishes  them  from  starch,  cellulose  and  resins. 
They  differ  from  the  sugars  by  being  incapable  of  fermentation  by 
yeast,  and  from  the  sugars  and  resins  by  their  insolubility  in  alcohol. 
From  dextrin  the  gums  soluble  in  water  are  distinguished  by  their 
laevorotatory  power  and  acid  reaction,  and  by  yielding  mucic  acid  on 
treatment  with  moderately  concentrated  nitric  acid.  Reichl  and 
Breinl  state  that  arabin  and  bassorin  are  distinguishable  from  dextrin 
by  the  blue  flocculent  mass  they  yield  when  heated  with  hydrochloric 
acid  and  orcinol,  dissolving  in  alcoholic  potash  to  form  a  violet  solu- 
tion showing  a  green  fluorescence.  Fragments  of  wood,  containing 
only  traces  of  wood-gum,  when  boiled  with  hydrochloric  acid  and 
orcinol  show  the  reaction  quite  distinctly.  From  erythrodextrin  and 
starch  the  gums  differ  by  giving  no  colour  with  solution  of  iodine,  and 
from  proteins  they  are  distinguished  by  not  yielding  ammonia  when 
ignited  with  soda-lime. 

The  gums  of  which  gum  arabic  is  the  type  are  dissolved  by  cold  water 
and  are  not  readily  precipitated  by  acids.  Pectin  forms  a  jelly  when 
its  aqueous  solution  is  faintly  acidified,  while  gum  tragacanth  merely 
swells  up  when  treated  with  cold  water  without  undergoing  notable 
solution. 

The  investigations  of  O'Sullivan  have  shown  that  the  gums  are  not 
carbohydrates  of  the  formula  (C6H10O5)n,  as  at  one  time  supposed, 
but  in  reality  glucosidic  derivatives  of  certain  organic  acids  and  built 
up  of  the  residues  of  sugar  molecules  united  by  ethereal  oxygen  to  the 
organic  acid.  This  acid  is  different  in  different  gums  and  is  to  be  re- 
garded as  the  nucleus  of  the  particular  gum;  thus  gum  arabic  contains 
arabic  acid,  C^HggC^;  geddah  gum  gives  geddic  acid,  an  isomeride 
of  arabic  acid;  gum  tragacanth  gives  bassoric  acid,  C14H20O13.  The 
commonest  sugars  in  gums  are  galactose  and  arabinose.  According 
to  Voley-Boucher  (Bull,  de  Sciences  Pharmacol.,  1908,  15,  394),  most 
gums  contain  a  soluble  enzyme  capable  of  decomposing  amygdalin. 
Soluble  gums  are  more  active  than  insoluble  ones. 


440 


STARCH   AND    ITS    ISOMERIDES. 


A  natural  gum  is  often  a  mixture  of  several  gum  compounds  differ- 
ing in  the  number  of  sugar  residues  in  their  molecules.  A  summary 
of  the  present  position  of  the  chemistry  of  the  gums  is  given  by  H.  H. 
Robinson  (Report  Brit.  Assoc.,  1906  (York),  227). 

In  analysing  gums  it  is  necessary  to  identify  the  sugars  and  the  gum 
acids.  The  principal  constants  of  a  gum  acid  are  its  ultimate  composi- 
tion, neutralising  power  for  bases  and  optical  rotation.  As  the  acids 
do  not  crystallise,  to  prove  their  individuality  it  is  necessary  to  precipi- 
tate them  fractionally  and  to  compare  the  constants  of  different  frac- 
tions. The  amount  of  mucic  acid  and  of  furfural  yielded  should  be 
also  determined.  The  following  analyses  of  some  tree  gums  are  due 
to  Huerre  and  Lemeland: 


Almond  tree 
(hard  gum) 

Almond  tree 
(elastic  gum) 

Apricot  tree 

Plum  tree 

Soluble  in  water, 

• 

Calculated  on  dry  gum, 

21.06 

8-9 

91.17 

79.16 

Insoluble  in  water, 

78.94 

91.1 

8.83 

20.84 

Loss  at  100°, 

15.76 

25.0 

16.14 

15.48 

Ash, 

2-34 

3-39 

2.52 

Galactans  as  galactose, 

23-7 

23.6 

16.36 

Pentosans  as  arabinose, 

54.6 

.... 

48.57 

76.35 

Total  sugars, 

85 

9i 

78.7 

94-8 

Sugars  identified, 

Arabinose 

Arabinose 

Arabinose 

Arabinose 

and 

and 

galactose 

galactose 

Gum  Arabic.  Gum  Acacia. — Gum  arabic  is  the  dried  exudation 
from  the  bark  of  various  species  of  Acacia.  Strictly  speaking,  "gum 
arabic"  is  the  generic  name,  "gum  acacia"  being  properly  limited  to 
the  superior  qualities  employed  in  medicine.  These  are  largely  ob- 
tained from  the  Soudan. .  The  finest  kind  of  gum  arabic  occurs  in 
commerce  in  lumps  of  various  sizes,  colourless  and  full  of  minute  cracks. 
Gum  Senegal  forms  yellowish  or  reddish  lumps,  often  of  the  size  of  a 
pigeon's  egg,  and  not  having  the  minute  cracks  of  the  better  varieties. 
It  is  less  readily  soluble  than  true  gum  arabic,  and  its  solution  soon  be- 
comes very  dark  in  colour. 

Gum  arabic  consists  essentially  of  calcium  arabate  or  arabic  acid 
(arabin),  which  may  be  obtained  pure  by  dialysing  a  solution  of  the 
gum  previously  acidulated  with  hydrochloric  acid.  The  colloid 
liquid  thus  obtained  is  laevorotatory,  and  is  not  precipitated  by  pure 
alcohol,  but  is  thrown  down  if  a  trace  of  any  acid  or  salt  be  present. 


GUM    ARABIC.  441 

After  being  evaporated  to  dryness  and  heated  to  100°,  arabin  does 
not  redissolve,  even  in  hot  water,  but  swells  up  into  a  gelatinous  mass, 
which  gradually  dissolves  on  treatment  with  alkalies,  or  alkaline 
earths,  in  presence  of  water,  yielding  a  liquid  indistinguishable  from 
the  aqueous  solution  of  ordinary  gum  arabic. 

Most  varieties  of  gum  arabic — including  the  Levantine,  Sennaar, 
East  Indian  and  Senegal — are  laevorotatory,  but  Australian  gum  is 
often  optically  inactive,  while  Gedda  gum  is  dextrorotatory.  Chem- 
ically, these  gums  are  analogous  to  the  dextrorotatory  varieties. 

The  inferior  qualtities  of  gum  contain  a  small  percentage  of 
a  reducing  sugar,  which  may  be  removed  by  treatment  with 
alcohol. 

The  sp.  gr.  of  air-dried  gum  arabic  ranges  from  1.35  to  1.49,  but 
when  completely  dried  at  100°  it  loses  about  13%  of  water,  and  the 
sp.  gr.  increases  considerably. 

Gum  arabic  has  a  very  faint  odour  and  a  mucilaginous  insipid  taste. 
It  dissolves  slowly  in  about  twice  its  weight  of  water,  forming  a  thick 
transparent  mucilage  of  acid  reaction.  Gum  is  slightly  soluble  in  di- 
lute spirit,  but  quite  insoluble  in  liquids  containing  more  than  60% 
of  alcohol,  and  is  precipitated  from  its  aqueous  solution  on  addition  of 
a  large  proportion  of  spirit. 

The  aqueous  solution  of  gum  arabic  is  not  precipitated  by  neutral 
lead  acetate,  but  with  the  basic  acetate  it  forms  a  white  jelly.  Its  solu- 
tion is  also  precipitated  by  potassium  or  sodium  silicate,  borax,  am- 
monium oxalate,  mercuric  chloride  and  ferric  salts. 

Suakim  gum,  which  is  quite  brittle,  is  often  not  wholly  soluble  in 
water,  but  yields  with  it  a  pasty  mass  of  rather  strong  acid  reaction, 
depositing,  when  diluted  with  water,  transparent  globules,  said  to  con- 
sist of  metagummic  acid  which  may  be  rendered  soluble  by  adding  a 
little  potash  or  lime-water. 

The  proportions  of  mucic  acid  obtainable  from  the  different  va- 
rieties of  gum  by  oxidation  with  nitric  acid  have  been  determined  by 
Kiliani  (Ber.,  1882,  15,  34),  who  found  amounts  varying  from  14.3%, 
from  a  sample  of  East  Indian  gum,  to  38.3%,  from  an  Australian 
sample.1 

^he  treatment  of  the  gums  with  nitric  acid  was  conducted  in  the  following  manner: 
2  grm.  of  the  powdered  sample  were  digested  at  60°  with  5  c.c.  of  nitric  acid  of  1.2  sp.  gr. 
until  the  whole  became  a  solid  mass  saturated  with  the  liquid.  Another  5  c.c.  of  nitric 
acid  were  then  added  and  the  liquid  filtered.  The  residue  of  mucic  acid  was  washed  thor- 
oughly, dried  at  100°,  and  weighed.  The  nitrate  and  washings  were  evaporated  together 
and  again  treated  with  nitric  acid,  when  a  further  quantity  of  mucic  acid  was  obtained 
while  a  third  treatment  generally  yielded  only  a  trace  in  addition 


442  STARCH    AND    ITS    ISOMERIDES. 

By  adding  a  saturated  solution  of  aluminum  sulphate  to  one  of 
gum  arabic,  the  adhesive  properties  of  the  latter  are  said  to  be  much  in- 
creased, owing  to  the  formation  of  aluminum  arabate,  while  calcium 
sulphate  is  gradually  deposited. 

The  presence  of  gum  arabic  in  a  solution  presents  the  formation  of 
a  number  of  characteristic  precipitates  (Lefort  and  Thibault,  Pharm. 
Jour.,  [3]  1882,  13,  301),  a  fact  which  is  of  importance  in  toxicological 
researches.  Thus,  in  presence  of  gum  arabic,  dilute  solutions  of  mer- 
cury, lead,  copper,  silver,  iron,  and  arsenic,  do  not  give  precipitates  with 
hydrogen  sulphide  or  alkaline  sulphides,  though  the  liquids  acquire 
a  colour  corresponding  to  the  sulphide  which  would  otherwise  be  pre- 
cipitated. The  precipitation  of  calcium  phosphate  and  uranyl  ferro- 
cyanide  is  prevented  in  a  similar  manner,  while  in  presence  of  gum 
arabic  the  alkaloids  are  not  precipitated  by  sodium  phosphomolybdate, 
potassium  mercuric  iodide  or  tannin. 

Assay  of  Gum  Arabic. — Gum  arabic  should  not  contain  more 
than  about  4%  of  ash.  It  should  be  soluble  almost  without  residue 
in  cold  water.  The  solution  should  be  free  from  starch  and  dex- 
trin, which  may  be  ascertained  by  the  negative  reaction  with  iodine 
solution;  but  should  be  rendered  turbid  by  oxalic  acid,  which 
the  solution  of  dextrin  is  not.  The  better  kinds  of  gum  arabic  do  not 
reduce  Fehling's  solution  when  heated  to  boiling  with  it,  any  red 
precipitate  being  due  to  the  presence  of  a  reducing  sugar,  small  quanti- 
ties of  which  exist  naturally  in  certain  inferior  varieties  of  gum, 
though  any  considerable  quantity  has  probably  been  introduced  as  an 
impurity  in  an  admixture  of  dextrin. 

According  to  Z.  Roussin  (J.  Pharm.  Chim.,  [4]  1868,  7,  251),  gum 
arabic  and  dextrin  may  be  distinguished  and  separated  by  means  of 
ferric  chloride,  which  precipitates  the  former  only.  The  solution  is 
concentrated  to  a  syrup,  mixed  with  ten  times  its  volume  of  rectified 
spirit,  and  the  resultant  precipitate  washed  with  rectified  spirit  and 
dried,  i  grm.  of  the  dry  residue  is  then  dissolved  in  10  c.c.  of  water, 
the  solution  mixed  with  30  c.c.  of  proof  spirit,  4  drops  of  ferric 
chloride  solution  (containing  26%  of  the  anhydrous  chloride)  added, 
followed  by  a  few  decigrammes  of  powdered  chalk;  and  after  stirring 
briskly  and  leaving  the  liquid  at  rest  for  a  few  minutes  it  is  filtered. 
The  precipitate  is  washed  with  proof  spirit,  and  the  dextrin  is  pre- 
cipitated from  the  filtrate  by  adding  very  strong  alcohol.  After  24 
hours  the  spirituous  liquid  is  decanted,  the  dextrin  dissolved  in  a 


GUMS.  443 

small  quantity  of  water,  the  resultant  solution  evaporated  at  100°, 
and  the  residue  weighed.  The  precipitate  containing  the  gum  must 
be  dissolved  in  dilute  hydrochloric  acid,  the  arabin  precipitated  by  add- 
ing absolute  or  very  strong  alcohol,  and  after  washing  with  spirit  is 
dissolved  in  water,  the  solution  evaporated,  and  the  residue  weighed. 
The  precipitation  of  gum  arabic  from  a  dilute  alcoholic  liquid  by  ferric 
chloride  and  chalk  is  so  complete  that  nothing  but  calcium  chloride 
can  be  found  in  the  nitrate,  while  the  precipitate  similarly  produced  in 
a  solution  of  dextrin  is  perfectly  free  from  the  latter  body.  By  the 
formation  of  a  cloud  on  adding  ferric  chloride  alone,  the  presence  of 
gum  arabic  is  sufficiently  demonstrated,  while  the  clouding  of  the 
nitrate  from  the  iron-chalk  precipitate  on  addition  of  alcohol  proves 
the  presence  of  dextrin. 

Another  test  by  which  gum  arabic  may  be  distinguished  from  dex- 
trin is  given  on  page  439.  A  large  proportion  of  dextrin  would  be  in- 
dicated by  the  dextrorotatory  action  of  the  solution,  but  the  differences 
in  the  optical  activities  of  natural  gum  arabic  and  commercial  dextrin 
prevent  the  quantitative  application  of  the  test. 

For  the  separation  of  gum  arabic  from  sugar,  Andouard  dilutes  10 
grm.  of  the  syrup  with  100  c.c.  of  spirit  of  0.800  sp.  gr.,  adds  20  drops  of 
acetic  acid,  and  stirs  vigourously.  After  3  hours  the  liquid  is  poured  on 
a  double  filter,  when  the  gum  forms  a  cake  which  readily  drains.  This 
is  dissolved  in  a  little  water,  and  the  precipitation  repeated,  the  pre- 
cipitate washed  with  alcohol,  dried  at  100°  and  weighed.  It  is  then 
exposed  to  the  atmosphere  for  24  hours,  when  it  will  have  taken  up  its 
normal  amount  of  moisture. 

The  inferior  kinds  of  gum  are  largely  employed  as  thickening  agents 
in  calico-printing.  Good  gum  neither  tarnishes  nor  alters  delicate 
colours  and  does  not  weaken  the  mordants.  The  action  of  gums  on 
delicate  colours  may  be  ascertained  by  printing  a  solution  of  the  sample 
mixed  with  cochineal-pink  or  fuchsine  upon  pure  wool;  the  fabric  is 
then  steamed  and  washed,  when,  if  the  gum  be  pure,  there  will  be  no 
trace  of  yellowness  apparent.  Too  great  an  acidity  of  the  gum  gives 
it  a  solvent  action  on  mordants,  and  hence  renders  it  unsuitable 
for  use. 

The  relative  viscosity  of  samples  of  gum  is  an  important  character 
in  judging  of  their  quality.  This  may  be  tested  by  making  solutions 
of  10  grm.  of  each  sample  in  a  little  warm  water,  diluting  the  liquids 
to  100  c.c.,  and  ascertaining  the  rate  at  which  the  solutions  flow  from 


444  STARCH   AND    ITS    ISOMERIDES. 

a  glass  tube  drawn  out  to  a  fine  orifice,  A  recently  prepared  solution 
of  gum  of  the  best  quality  should  be  used  as  a  standard. 

Gum  tragacanth  is  the  gummy  exudation  from  certain  species  of 
Astragalus.  It  occurs  in  flattened,  tear-like  masses,  strings  or  curved 
bands,  which  are  usually  marked  with  ridges  or  other  indications  of 
lamination. 

According  to  Giraud,  gum  tragacanth  usually  contains  about  60% 
of  a  pectinous  body  which  yields  pectic  acid  by  boiling  with  water 
containing  i%  of  hydrochloric  acid;  from  8  to  10%  of  soluble  gum, 
probably  arabin;  5  to  6%  of  starch  and  cellulose;  3%  of  ash;  20%  of 
water,  and  traces  of  nitrogenous  bodies.  The  ash  is  chiefly  calcium 
carbonate. 

The  characteristic  pectinous  constituent  of  gum  tragacanth  is  known 
as  tragacanthin,  adracanthin,  or  bassorin,  and  is  stated  to  have  the 
composition  C12H20O10. 

Tragacanth  is  usually  white  or  yellowish  (having  sometimes  been 
bleached  by  chlorine),  but  the  inferior  varieties  have  a  brownish 
colour.  It  is  hard,  tough  and  difficult  to  powder.  Tragacanth  is 
odourless  and  tasteless  and  insoluble  in  alcohol  or  ether.  With  50 
parts  of  water  it  swells  up  and  forms  a  thick,  jelly-like  mucilage,  with- 
out actually  dissolving.  When  diffused  through  a  much  larger 
quantity  of  water  it  forms  a  ropy  liquid  which  may  be  passed  through 
.a  filter,  leaving  an  insoluble  residue  which  is  coloured  blue  by  iodine 
from  the  presence  of  starch.  Mucilage  of  tragacanth  is  coloured  yellow 
by  caustic  soda,  and  a  solution  of  the  gum  yields  clear  mixtures  with 
borax,  alkaline  silicates,  and  ferric  chloride,  but  is  precipitated  by 
alcohol.  It  becomes  thick  on  adding  neutral  or  basic  lead  acetate,  and 
on  heating  the  mixture  a  precipitate  is  formed. 

Before  being  used  for  calico-printing,  gum  tragacanth  is  swelled  by 
soaking  in  cold  water  for  24  hours,  and  afterwards  boiled  with  water 
for  6  hours,  when  a  thick  homogeneous  solution  results,  which,  how- 
ever, has  but  little  cohesive  power.  The  comparative  viscosity  of  the 
liquid  can  be  ascertained  as  in  the  case  of  gum  arab'c  (page  443). 

To  distinguish  gum  acacia  and  gum  tragacanth  advantage  is  taken 
•of  the  fact  that  the  latter  contains  no  active  oxidase  such  as  is  present 
in  gum  acacia.  A  cold  aqueous  solution,  i  in  30  of  the  gum,  is  treated 
with  an  equal  volume  of  i  %  aqueous  solution  of  guaiacol ;  i  drop  of 
hydrogen  peroxide  solution  is  then  added  and  the  mixture  shaken. 
In  presenc^  of  gum  acacia  the  liquid  rapidly  acquired  a  brown  tint, 


PROXIMATE    ANALYSIS    OF    PLANTS.  445 

whilst  with  pure  gum  tragacanth  it  remains  colourless.     (Payet,  Ann. 
Chim.  Anal.,  appl.  1905,  10,  63.) 

The  gum  of  Cochlospernum  gossypinm  is  remarkable  for  its  power 
of  slowly  giving  off  acetic  acid  when  exposed  to  moist  air  or  on  hydroly- 
sis (H.  H.  Robinson,  Trans.  Chem.  S0r.,  1906,  89,  1496).  It  yields 
further  a  gum  acid  (gonadic  acid),  xylose  and  galactose.  This  property 
is  also  possessed  by  the  gum  of  Stercidia  urens. 

PROXIMATE  ANALYSIS  OF  PLANTS. 

The  analysis  of  plants,  as  a  rule,  resolves  itself  into  the  qualitative 
detection  and  quantitative  separation  of  some  single  substance  or 
group  of  substances.  So  far  as  the  carbohydrates  are  concerned  the 
subject  has  been  fully  dealt  with  in  the  preceding  pages  and  the 
alkaloids  and  similar  groups  of  substances  will  be  treated  elsewhere. 
At  the  present  time,  biological  methods  are  much  used  and  it  is  also 
becoming  customary  to  test  plants  for  enzymes. 

The  following  scheme,  as  practised  in  the  laboratory  of  Prof.  A.  B. 
Prescott,  is  intended  to  facilitate  the  systematic  analysis  of  vegetable 
substances.  Substances  having  by  its  aid  been  proved  to  be  present 
should  be  isolated  by  methods  specially  devised  for  each  individual  case. 
Owing  to  the  very  rapid  changes  which  take  place  in  plants  after  being 
gathered  or  on  being  macerated  with  water  owing  to  the  action  of  en- 
zymes, it  is  often  advisable  to  destroy  the  enzymes  immediately;  this  is 
conveniently  done  by  dropping  the  freshly  cut  plant  piecemeal  into 
boiling  alcohol. 

Moisture  is  estimated  by  methods  given  on  page  64.  The  loss  of 
weight  may  include  a  little  volatile  oil. 

Total  nitrogen  is  obtained  by  the  Kjeldahl  process.  This  is 
multiplied  by  6.33  to  convert  it  into  proteins.  It  must  not  be 
assumed,  however,  that  all  the  nitrogen  present  exists  as  proteins, 
the  contrary  being  commonly  the  case.  An  outline  of  the  method 
of  estimating  the  nitrogen  existing  in  various  forms  is  given  by  Schulze 
and  Barbieri  (Landw.  Versuchs-Stat.,  1881,  26,  213),  but  if  alkaloids 
are  present  they  must  be  isolated  by  separate  means. 

Action  of  Solvents. — The  substance  is  then  submitted  to  a  sys- 
tematic treatment  with  solvents  and  reagents  in  the  manner  prescribed 
in  the  following  tables: 


446 


STARCH   AND    ITS    ISOMERIDES. 


H   S 

ii 

^    o 


O     o 

g.a 


§'5 


-Tb 

43  > 


T3    3    c3 
C  "o    ^ 

5  8  S 

(-i    0) 

^3^ 

y3  -r-   ea 


. 


i  o  «*§ 

I  <u  -y  a 

t3  C  J3      OH 

•S  aj  ^3  :r 


s 


0C3 


cq 


iiljililiVII 

|  3  E-M  S'&c  g-aSS 
<o 


i  -  i 

cb  6 


H  ° 


a 


ft  ill1 


•  44 -4? 

g      »     ^•G-SS* 
l|    £§•'§! 


f 


PROXIMATE   ANALYSIS    OF    PLANTS. 


447 


s 


g! 

K-3 

.  £ 
£  8. 

IE 


2   £ 

<->  H 

•5  -  I 


.£'3 


o  o 


£   u 

IS 


.s  « 

I* 

t«! 

^3.2    1 


1 


0)   ^J  Z 


2  -a 

3| 

•si 


a  known  meas 
urs.  Then  fil 


.jLs' 

43         0-4*0 

•2P3  .2 ' 

(U   en   _ 


-2  2 


2|o| 

y^t 


9 


tit 

'  *- 


•~-^ 


i 


5  c«" 

is 


Y-S  -P 

tg  1- 

p  *S  I   flc 

:p4      «*->  I 


pi- 
ill 


>•  u  .> 

-o  d  5c 

!|f 

!%~ 


Il 
' 


1=.S 


^  s 
si 


2a3 


QJ 


•S     |.2^S^S 

slli-gafjrS 


CJ 

f-i  6 


—        JH  g 


^'ife 

•sl'l'se 


448 


STARCH   AND    ITS    ISOMERIDES. 


-O  6 

§8 


00 

" 


=5  <u  a 


"§• 


c^    O    O^ 
i— i    O  *  *~| 

a>  <u  , — i 

U  X3    cu 


CO     OT  ^ 

°9   ^-^ 


S-g  c 


o  i*  S 


o  -- «  •* 
S  f  o 

g  b-c 

C/3 


or  tannin  i 
se  process  b 


3  O, 

^ 

hH    <U 

fj 


ill 


±na 

?'o 


gg 


Illlsfluillllil^^ 


»z 

.s 


Jj|  if  11  g  E  £  rt  o  1  sVl'1-S.y  8  ?*' 

|lKIilil«^ll!lIlllll 

to 


"I  OlFil^'SlftrifiPl 

E..o2°'..i   'Ro«»'S«S5Ss    ^5£S«« 

ilPfliii:liiJ:i:.|8!iiii 


11 


o>--  . 


^IlMlllBEi1®! 


1  §  §^  !lf  lll  Oil  .  1 


- 

10  H 


1 


'|S| 

^   8,-S    rt^HH1"    60^1    °    * 


PROXIMATE   ANALYSIS    OF    PLANTS. 


449 


0        .  rt 

-    §    e    E 

=  '5  '1  -2 

11 


- 


.S  £  .8 

J  3   g 

C  3      « 

o  ^  "c 


a 

It-1      O 
CJ 


•c  g 

Q    S 


>      0 

=3  ~ 


3 

"c 
> 

d 

o 
d 
-* 


3  .22 

T3  -3 

'35  TJ 

cu  o 

II 

si 

II 

bJO^ 

d    <*» 

en 


IS 

cr1  d    o> 

—  o    rf 

a,  cu.y 

Z3  c^    nj 

«  «    .S 


0      ^ 


^  -a 

CTJ       d 
CJ      rt 

S  -d* 
S  J 

1  1 

O    i— i 

s  ^ 
:&? 

s  ^ 

CH   ^ 

CU     '3-, 

5  & 


c 
t> 

CO 

U 


' 


° 


en     o 

§•§ 

U       CJ 

cu   13 

I    <0 

.a-  cu 

£  S 

IH     tn 

o-  S 

i  E 

2    w 

.S  'ti 

5  s 

SoS 


J3        *  . s 

j  i  ^  |  i 

o    "Si 


.     cu 

W3      -*J 

e   3  T3  •» 


<Z>     13     'Tj 
^     <     < 


rf     ~  °          ^ 

§  -a  -2  8  a 

o  't?    o    ^  "O 


1/5 
JH 

§ 

I 

^ 

'o 
> 

_c 

'S 

1 

C/3 

2 

DH 

13 

d 

rs 

'3 
.? 

M 

S 

5 
C 

d 

0 

annin. 

iii^i; 


en    T5 
£     d 


rH  WJ       VH       ^  O 

|    o    x  M  'g  •£)  " 
•H   u.-°   A'-l  -S  -g 


g 

£  ,3  *So 
o    W)  «c 


v^ 

ili 

*S    X5    .^      t«      0     -5 


^      CA       >** 
V       V     -S^ 


H 


.S    J3      S     S 

"S  -s  -  g 

b^  ^  sa  J§ 


d          i 


-s  -a 

^  T3 

Q    d 


*' 


§'•3 


a  ° 

CO 

o    t* 

•»->      — ' 

c3      CJ 

It 


i.J 

O     **-* 

^       CH 

il 
i! 

t  3 
a"8 

d  3 

<     en 

R   »r 


$2 

S| 
Si 

si 


a 


i-i 
g! 

8 

CO 


W 


VOL  i — 29 


45°  STARCH   AND    ITS    ISOMERIDES. 

J.  M.  Albahary  (Conipt.  rend.,  1908,  146,  336)  has  recently  given 
the  following  scheme  for  the  complete  analysis  of  vegetable  substances. 
A  portion  is  dried  at  100°  to  obtain  the  quantity  of  volatile  matter, 
and  is  then  incinerated  to  give  the  amount  of  total  ash.  A 
second  portion  of  the  sample  is  extracted  with  alcohol;  the  alcoholic 
extract  is  distilled  at  a  low  temperature,  and  the  distillate  is  collected 
in  a  receiver  containing  a  known  volume  of  standard  sodium  hydroxide 
solution  and  surrounded  by  a  freezing  mixture.  On  titrating  back  the 
excess  of  sodium  hydroxide,  the  quantity  of  volatile  acids  is 
obtained,  and  this  added  to  the  weight  of  the  residue  remaining 
in  the  distillation  flask  gives  the  weight  of  the  alcohol-soluble  sub- 
stances. The  sum  of  the  substances  soluble  and  insoluble  in  alcohol 
subtracted  from  the  weight  of  the  original  material  gives  the  actual 
amount  of  the  fat,  colouring  matters,  cholesterol  and  lecithin.  The 
portion  of  the  substance  insoluble  in  alcohol  is  next  digested  for  2  days 
in  alcohol  acidified  with  hydrochloric  acid.  The  solution  is  then 
poured  through  a  filter  and  the  residue  is  washed  with  alcohol.  The 
filtrate  and  washings  are  evaporated,  the  residue  is  weighed,  extracted 
with  ether  to  remove  organic  acids  and  then  dissolved  in  water.  Por- 
tions of  the  solution  are  used  for  the  estimation  of  the  reducing  sugars, 
mineral  acids,  nitrogen,  asparagine,  sulphur  and  ash.  In  the  portion 
insoluble  in  acidified  alcohol  are  estimated  the  total  protein,  nuclein, 
albumin,  starch,  cellulose,  etc. 

The  following  books  will  be  found  to  give  useful  special  information. 
For  general  morphological  and  microscopic  character  of  plants  see 
Wiesner,  Die  Rohstoffe  des  Pflanzenreiches;  for  microscopic  identi- 
fication of  technical  fibres  see  Franz  von  Hohnel,  Die  Mikroscopie 
der  technisch-verwendeten  Faserstojje. 

CEREALS. 

Owing  to  the  defective  methods  employed,  many  of  the  older  analy- 
ses of  wheat  and  other  grains  are  of  doubtful  value. 

A.  H.  Church  gives  the  following  analyses  by  himself  in  illustration 
of  the  composition  of  representative  specimens  of  the  cereal  grains  and 
products  therefrom: 


CEREALS. 


451 


•9 

^ 

d 

, 

~ 

0) 

*C   |_ 

^  o 

2 

CQ 

^ 

u 

n 

_o 

o 

*j5 

cfe 

| 

o  6 

Is 

% 

V 

| 

•g 

£ 

£ 

^ 

^ 

OH 

X 

0 

3 

i 

Q 

Water  

14-5 

13  .0 

14.0 

S-o 

14  6 

13.0 

14.6 

14.5 

13-° 

12  .2 

Proteins  and  other  nitro- 

genous bodies  

II  .0 

10.5 

IS  -0 

16.1 

6.2 

10.5 

7-5 

9  .  o 

IS  -3 

8.2 

Starch    with     traces     of 

Dextrin    etc 

69  .  o 

74  •  "? 

44  -O 

63  .0 

76  .0 

71  .0 

76  .0 

64.5 

61.6 

70  .6 

Fat  

I  .2 

0.8 

4.0 

10.  I 

i-3 

1.6 

o-S 

5-o 

4.2 

Cellulose  and  Lignose  .  .  . 
Mineral  matter  

2.6 

i  .  7 

0.7 
0.7 

6.0 

2  .  I 

0.8 
i  .  i 

1.6 

0.5 

2  .0 

3-5 
1.6 

i  •  7 

IOO  .  O 

IOO  .O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

For  convenience  of  comparison,  the  following  analyses  of  other  vege- 
table products  are  given.  They  are  selected  from  among  a  large  num- 
ber published  in  Church's  work  on  Food: 


Buck- 
wheat 

Peas 

Haricot 
beans 

Lentils 

Earth- 
nut 
shelled 

Water 

I  7      A 

14.  3 

14.0 

14    ^ 

7r 

Proteins 

15.  2 

22    4 

23    O 

24  o 

24    ^ 

Starch 

61  6 

51  3 

40.  o 

II    7 

Fat  
Cellulose  and  lignose  

3-4 

...             2.1 

2-5 

6  < 

2-3 
c  .  c 

2.6 

6.0 

5O.O 

4  •  5 

Mineral  matter  

2.3 

3-° 

2-9 

3-° 

1.8 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

IOO.O 

Potatoes 

White 
turnips 

Carrots 

Beet-root 
Red 

Yam 

Water     

! 
7^-0 

02.8 

80.0 

82.0 

78  6 

Proteins  

...             2  .  3 

O.  =C 

o.  5 

o.  4 

2    2 

Susrar 

4r 

JO    O 

Starch 

l6    3 

Dextrin,  gum  and  pectose.  .  . 
Fat                   

2.0 
O    3 

4.0 

O    I 

O    2 

3-4 

O    I 

O    ? 

Cellulose  and  lignose 

I    O 

i  8 

4-7 

30 

Alineral  matter 

I    O 

o  8 

•o 
I    O 

•" 

o  o 

j      C 

More  recent  analyses  have  been  published  by  the  United  States  De- 
partment of  Agriculture,  from  the  bulletins  of  which  the  following 
figures  are  taken: 

1  One  hundred  pounds  of  oats  yield  about  60  of  oatmeal  and  26  of  husks,  the  remainder 
being  water  and  loss. 

1  The  product  called  pearl  barley  constitutes  only  about  one-third  of  the  whole  seed. 


452 


STARCH   AND    ITS    ISOMERIDES. 
COMPOSITION  OF  CEREAL  GRAINS. 


Carbohy- 

Moist- 
ure 

Pro- 
teins 

Ether 
ex- 

Crude 
fibre 

Ash 

drates 
other 
than 

(6.25N) 

tract 

crude 

fibre 

Typical  unhulled  barley  .  .  .  ,  

10.85 

II  .O 

2.25 

3-85 

2-5 

69-55 

Typical  American  maize  

10.  75 

IO.O 

4.  2? 

i  .  75 

i  .  c; 

71  .75 

Typical  wheat  

10.6 

12.25 

•?     "O 

1-75 

2.4 

o 

7I-25 

Sweet  corn,  19  samples  (Richard- 

son)   

8  44 

11.48 

8  57 

2.82 

I   07 

66.72 

Typical  American  buckwheat  .... 

"*  *  fr 

12.0 

IO-75 

O/ 
2.0 

i°-75 

v  / 

/  * 

62.75 

Typical  unhulled  oats  

10.  O 

12.0 

4-5 

12.  O 

3-4 

58.0 

Typical  rye  

IO-S 

12.25 

i-5 

2.  I 

1.9 

7J-75 

Typical  rice  unhulled 

IO  .  C 

7  •  5 

1.6 

0    O 

4.0 

67   4 

Typical  rice,  hulled  but  unpolish- 

V • 

w  /  •  T- 

ed  

12.  O 

8.0 

2  .O 

I  .O 

i  .0 

76  o 

Typical  rice,  polished  

12-4 

7  .  ^ 

0.4 

0.4 

o.  c 

/       • 

78  8 

/     0 

0 

/ 

COMPOSITION   OF  FLOURS. 


Moisture 
Max.       Min. 

Ash 
Max.  Min. 

Proteins 
(6.25  N) 

Max.       Min. 

Fibre 

Max.  Min. 

'  Ether 
Extract 

Max.  Min. 

N-free 
Extract 

Max.       Min. 

Wheat  
Rve.  . 

15.0       9.0 
14.0     12.  o 
15.0     10.0 
18.0     12.5 
15.0     10.0 
10.0       6.0 
18.0       8.0 
15.0     ii.  o 

0.8     0.3 
1-5     0-5 

2.0       I.O 

1.5     0.8 
0.6    0.3 

2-4       2.0 

4.5     i.o 

2.2       1.8 

15.0       8.0 
ii.  o       6.0 
12.0       8.5 

9-5       S-o 
10.0       7.0 
18.0     14.0 
11.5       8.0 
15.0     10.0 

I.O      O.I 

0.6     0.4 
0.6     0.3 
0.6     0.3 
0.4     o.i 
1.4     0.7 
3-5     0.7 

2.4       2.O 

2.0     0.5 
i.o     0.9 
2.0     0.5 

2.0      0.8 

0.6     0.3 

9-5     6-5 
6.0     2.5 

2.2       1.9 

90.0     82.0 
92.0     88.0 
92.0     87.0 
93.0     84.0 
90  .  o     85  .  o 
76.0     72.0 
80  .  o     63  .  o 
72.0     70..  o 

Barley  
Buckwheat  .... 
Rice 

Oat  (meal)  .... 
Maize  (meal)  .  . 
Graham  

Proteins  of  Cereals. — Although  cereals  are  mainly  composed  of 
starch,  it  is  the  protein  constituents  which  often  impart  to  them  their 
characteristic  properties  and  which  therefore  are  investigated  in  an 
analysis.  Indeed,  in  very  many  of  the  published  analyses,  the  starch 
is  determined  by  difference.  Although  different  proteins  occur  in  dif- 
ferent cereals,  many  of  the  proteins  contain  about  15.8%  of  nitrogen  and 
it  has  become  usual  to  deduce  the  proportions  of  proteins  present  by 


multiplying  the  percentage  of  nitrogen  by  6.33 


100 


This  pro- 


cedure ignores  the  fact  that  the  whole  of  the  nitrogen  of  plants  does 
not  exist  in  the  form  of  proteins  and  may  be  very  misleading  if  the 
analysis  is  used  to  judge  of  the  suitability  of  a  cereal  for  bread  mak- 


FLOUR.  453 

ing  or  its  food  value.     For  wheat  proteins  the  factor  5.7  is  considered 
more  accurate. 

This  subject  will  be  fully  dealt  with  in  Volume  VIII. 

WHEAT. 

Two  varieties  of  wheat — Triticum  -vulgar e — are  cultivated,  distin- 
guished as  spring  and  winter  wheat.  Individual  species  and  sam- 
ples differ  rather  widely  in  composition.  Konig's  table  for  the  mean 
composition  of  wheat  from  250  analyses  is  quoted  here. 

Water,  13.56% 

Proteins,  12.42% 

Fat,  i .  70% 

Starch,  64.07% 

Sugar,  i-44% 
Gums  and  dextrin,    2 . 38% 

Fibre,  2 . 62% 

Ash,  i .  79% 

Ground  wheat  free  from  bran  is  termed  flour.  The  commercial 
value  of  wheaten  flour  depends  on  the  colour  and  texture  and  upon  the 
quality  and  to  some  extent  the  quantity  of  the  contained  gluten.  In 
practice  the  somewhat  elastic  term  "strength"  is  employed,  which  is 
denned  as  the  power  of  flour  to  give  a  shapely  well-risen  loaf  (Hum- 
phries and  Biff  en)  or  as  the  power  of  flour  to  absorb  water  when  made 
into  dough  (Jago).  Bakers  prefer  a  flour  with  a  high  percentage  of 
tenacious  gluten.  The  causes  of  strength  are  as  yet  imperfectly  un- 
derstood. 

FLOUR. 

Good  wheat  flour  should  be  an  almost  perfectly  white  impalpable 
powder  with  only  the  very  faintest  yellow  tinge.  When  pressed 
smooth  by  means  of  a  polished  surface,  no  traces  of  bran  should  be 
visible;  it  should  have  a  sweet  odour  and  flavour  and  be  free  from 
acidity.  When  comparing  flours  the  following  tests  may  be  made: 

Colour. — Small  wedge-shaped  heaps  with  a  smooth  surface  are 
arranged  side  by  side  on  a  sheet  of  glass  and  the  colours  compared 
when  dry  and  after  carefully  immersing  the  plate  in  water,  when,  as  a 
rule,  the  colours  are  much  more  marked. 


454  STARCH   AND    ITS    ISOMERIDES. 

Doughing  Test. — A  known  weight  of  the  sample  is  made  into  a 
dough  with  1/2  to  2/3  its  weight  of  water  and  the  colour  and  "feel," 
that  is  firmness,  elasticity  and  compactness,  of  the  doughs  are  compared. 

Gluten  Test. — To  obtain  results  comparable  at  different  dates  much 
care  must  be  paid  to  detail  in  carrying  out  this  test.  About  30  grm. 
of  flour  are  made  to  a  stiff  dough  with  12-15  c-c-  water  and  allowed 
to  stand  for  i  hour.  The  mass  is  then  carefully  kneaded  in  a  stream 
of  running  water  until  all  the  starch  has  been  removed.  This  kneading 
is  conveniently  carried  out  between  the  fingers,  the  flour  being  held 
over  a  sheet  of  fine  muslin  which  allows  the  starch  to  pass  but  retains 
any  particles  of  gluten  which  may  fall  on  it.  Other  operators  advise 
kneading  the  flour  wrapped  in  a  piece  of  linen.  The  ball  of  fresh  glu- 
ten thus  obtained  should  be  tough  and  elastic,  capable  of  being  pulled 
out  in  threads  and  but  little  coloured.  Flour  from  English  wheats 
gives  a  very  soft  and  sticky  gluten  showing  very  little  elasticity,  whereas 
that  from  Canadian  spring  wheats  is  very  tough  and  elastic.  After 
washing,  the  gluten  is  left  for  an  hour  under  water,  the  excess  of  moist- 
ure is  then  removed  between  the  hands  as  far  as  possible  and  the  wet 
gluten  weighed.  It  is  then  dried  for  40  hours  at  98°  C.  or  for  a  shorter 
period  at  a  higher  temperature  and  the  weight  of  dry  gluten  determined. 

This  crude  gluten  consists  in  reality  of  true  gluten  together  with 
small  percentages  of  non-gluten  proteins,  mineral  matter,  fat,  a  little 
starch,  fibre,  etc. 

ANALYSIS  OF  FLOUR. 

1.  Moisture  is  determined  by  heating  at   100°  until  no  further 
loss  in  weight  occurs. 

2.  Fat  is  determined  by  ether  extraction  of  the  dry  flour.     A  high 
value  for  the  ether  extract  of  a  patent  flour  (above  1.5%)  indicates  in- 
complete removal  of  germ  particles. 

3.  Gluten   may   be   estimated   approximately   by  washing  as  de- 
scribed   above    or   by    a    nitrogen   determination    on    the    original 
flour.     The  percentage  of  nitrogen  found  is  multiplied  by  the  factor 
5.7.     (This  is  preferable  to  6.33  in  the  case  of  wheat.) 

4.  Ash  is  best  determined  in  a  muffle  or  the  flour  may  be  mixed 
with  ammonium  nitrate  and  burnt.     If  above  i%,  mineral  adulteration 
is  probably  present. 

5.  Starch  may  be  estimated  by  one  of  the  methods  already  described, 
see  page  420. 


FLOUR.  455 

6.  Gliadin  may  be  determined  by  extracting  with  70%  (by  volume) 
alcohol  for  2  hours  and  determining  nitrogen  in  the  nitrate.     This 
is  multiplied  by  the  same  factor  as  the  gluten  nitrogen. 

7.  Cold  water  extract,  which  consists  of  sugars,  soluble  proteins 
and  potassium  phosphate,   etc.,  is  obtained  by  digesting  flour  with 
a  large  volume  of  water,  filtering  and  evaporating  an  aliquot  portion 
in  a  weighed  dish.     The  residue  is  ignited    to  give  the  soluble  ash. 
The  result  depends  largely  on  the  temperature  and  time  of  extraction, 
as  under  these  conditions  the  diastatic  capacity  of  a  flour  causes  a  rapid 
increase  in  the  amount  of  soluble  sugar. 

8.  Acidity  is  best  determined  by  direct  titration  with  decinormal 
alkali,   using  phenolphthalein  as  indicator.     Normal  wheat  has   an 
acidity  0.16   to  0.25%,  calculated  as  lactic   acid.     20  grm.   of   flour 
are  shaken  with  200  c.c.  of  water  for  2  hours  filtered  and  50  c.c.  of 
the  filtrate  titrated.     The  test  is  most  useful  for  detecting  unsound 
wheat  and  flour. 

9.  Diastatic  Power. — 0.4  gram,  flour  and  200  c.c.  of  a  2  %  solu- 
tion of  soluble  starch  are  maintained  for  an  houi  at  15.5°.     Action  is 
stopped  by  a  drop  of  ammonia  and  portions  of  2  c.c.  are  heated  in 
test-tubes  in  boiling  water  for  5  minutes  with  different  quantities  of 
Fehling's  solution  to  determine  the  amount  which  is  just  reduced  by 
the  sugar  formed.     The  diastatic  power  is  100  when  2  c.c.  reduce 
4  c.c.  of  Fehling's  solution.     It  ranges  in  commercial  flours  from  25 
to  60. 

Gluten  consists  of  two  proteins:  gliadin,  remarkable  for  its  solu- 
bility in  dilute  alcohol,  and  glutenin,  which  is  soluble  in  very  dilute 
alkali.  Gliadin  in  the  hydrated  condition  is  a  soft,  sticky  substance 
which  can  readily  be  drawn  into  threads,  when  dehydrated  it  forms 
a  white  friable  mass.  It  may  be  prepared  by  extraction  of  flour  or 
gluten  with  70%  (by  volume)  alcohol  and  precipitation  from  this  solu- 
tion by  sodium  chloride.  It  is  readily  soluble  in  pure  water.  Gliadin 
forms  a  sticky  mixture  with  water,  and  the  salts  naturally  present  in 
the  flour  prevent  its  solution.  The  glutenin  imparts  solidity  to  the 
gluten,  evidently  forming  a  nucleus  to  which  the  gliadin  adheres. 

The  ratio  of  gliadin  to  total  gluten  varies  in  different  flours  and  au- 
thorities are  not  agreed  as  to  the  correlation  of  this  ratio  with  strength. 
A  flour  with  a  high  gliadin  ratio  is  considered  the  best:  Fleurent  sug- 
gests 75%,  Snyder  60%,  but  these  values  are  not  accepted  by  authori- 
ties in  England. 


STARCH   AND    ITS    ISOMERIDES. 

Mineral  Constituents  of  Wheat  and  Flour.— Whole  wheat  con- 
tains a  much  higher  percentage  of  ash  than  flour.  The  ash  of  wheat 
ranges  from  1.4  to  1.9%,  and  that  of  good  flour  seldom  exceeds  0.7% 
or  0.85%  in  the  case  of  seconds  flour.  It  may  be  safely  assumed  that 
any  flour,  free  from  a  notable  proportion  of  bran,  which  yields  a 
higher  ash  than  i%  is  adulterated. 

Blythe  quotes  the  following  table  as  the  mean  composition  of  the 
ash  of  entire  wheat: 

Winter  wheat.      Summer  wheat. 
Potassium  oxide,  31.16  29-99 

Sodium  oxide,  2.25  1.93 

Calcium  oxide,  3-34  2  •  93 

Magnesium  oxide,  Ji-97  12.09 

Ferric  oxide,  1.31  .51 

Phosphoric  oxide,  46.98  48.63 

Sulphur  trioxide,  .37  1-52 

Silica,  2. 1 1  1.64 

Chlorine,  .22  .48 

According  to  Snyder,  the  ash  of  wheat  flour  bears  a  proportion  to 
the  grade — the  lower  the  grade  the  higher  the  percentage  of  ash. 
First  patents  have  less  than  0.4%,  second  patents  less  than  0.5%  and  a 
straight  grade  flour  should  not  have  more  than  0.55%  of  ash.  Mixing 
or  misbranding  of  flours  can  be  more  accurately  determined  in  this 
way  than  by  any  other  means.  The  figures  quoted  refer  to  hard 
Canadian  spring  wheat. 

The  United  States  standard  of  purity  is  not  more  than  13.5%  of 
moisture,  i%  of  ash  and  0.5%  of  crude  fibre  and  not  less  than  1.25%  of 
nitrogen. 

Adulterations  of  Flour. — Flour  may  be  adulterated  with  mineral 
matters  to  increase  its  weight,  with  alum  or  copper  sulphate  to  improve 
its  appearance  or  with  cheaper  flours  or  starches.  In  exceptional  cases 
it  may  contain  weeds  or  have  been  damaged  by  mould  and  contain  ergot. 

The  amount  of  ash  affords  a  convenient  and  accurate  means  of  de- 
tecting mineral  adulterants  with  the  exception  of  alum  which  is  usually 
employed  in  too  small  a  quantity  sensibly  to  affect  the  percentage  ob- 
tained. The  mineral  adulterants  may  be  separated  from  a  flour  by 
shaking  it  with  chloroform  in  a  separating  funnel  and  leaving  it  till 
the  flour  has  risen  to  the  surface.  Any  mineral  adulterant  sinks  in  the 


FLOUR.  457 

chloroform  and  may  be  removed  and  examined.  It  is  further  purified 
by  a  second  treatment  with  chloroform;  the  residue  is  obtained  on  a 
watch-glass,  the  chloroform  removed  by  evaporation,  and  the  solid 
weighed. 

Alum  or  other  crystalline  matter  is  detected  by  microscopic  ex- 
amination; the  residue  is  dissolved  in  a  little  cold  water  and  filtered 
and  the  insoluble  matter  ignited  and  weighed.  It  should  not  exceed 
0.1%,  if  the  flour  is  free  from  insoluble  mineral  adulterant.  The  solu- 
tion is  evaporated  to  dryness  and  the  crystals  of  alum  observed; 
they  may  be  tested  for  aluminium,  sulphates,  potassium  and  ammo- 
nium or  the  alum  may  be  recognised  by  its  astringent  taste  and 
reaction  with  logwood. 

Logwood  Test  for  Alum. — i  grm.  of  freshly  cut  fine  logwood  chips  is 
digested  for  10  hours  in  30  c.c.  alcohol;  10  c.c.  of  this  extract  are  mixed 
with  150  c.c.  water  and  10  c.c.  of  a  saturated  solution  of  ammonium 
•carbonate;  50  grm.  of  flour  are  made  into  a  thin  paste  with  water,  a 
few  drops  of  fresh  x  alkaline  logwood  solution  added  and  the  mixture 
put  aside  for  some  hours.  Alum  produces  a  lavender-blue  lake,  pure 
flour  a  pinkish  colour  which  fades  to  a  dirty  brown.  The  test  is  sensi- 
tive to  y^nnnr  part  of  alum.  The  blue  colour  should  remain  when 
the  sample  is  heated  for  an  hour  or  two  in  the  water-oven. 

Wynter  Blythe  uses  small  strips  of  gelatin  on  which  to  concentrate 
the  alum.  A  strip  is  soaked  for  12  hours  in  the  cold  extract  of  the 
suspected  flour  and  then  taken  out  and  steeped  in  the  ammoniacal  log- 
wood, when,  if  alum  is  present,  it  acquires  a  very  marked  blue  colour. 
The  strips  may  be  washed,  dissolved  in  hot  water  and  the  absorption 
.spectrum  of  the  solution  observed. 

Alum  acts  in  increasing  the  whiteness  and  improving  the  apparent 
quality  of  inferior  flour.  Its  presence  in  flour  or  bread  is  always  to 
be  regarded  as  a  sign  of  adulteration.  (See  under  Bread.) 

Copper  Sulphate  can  be  detected,  even  when  present  in  but  very 
minute  proportion,  by  soaking  the  bread  in  a  solution  of  potassium 
ferrocyanide  acidulated  with  acetic  acid,  when  a  purplish  or  red- 

*In  employing  the  logwood  test  for  alum,  it  is  very  important  that  the  tincture  of  log- 
wood should  be  freshly  prepared,  and  that  the  test  should  be  made  immediately  after  mix- 
ing the  logwood  tincture  with  the  solution  of  ammonium  carbonate.  Inattention  to  these 
essential  points  has  caused  the  failure  to  obtain  the  blue  with  specimens  undoubtedly 
containing  alum.  The  subsequent  drying  also  should  never  be  neglected.  With  proper 
-care,  the  test  is  exceedingly  delicate,  0.02%  of  alum  causing  a  distinct  shade  of  blue,  while 
with  three  or  four  times  this  proportion  the  reaction  is  wholly  beyond  question. 

On  the  other  hand,  a  blue  colouration  of  bread  and  flour  by  an  ammoniacal  solution  of 
logwood  does  not  infallibly  prove  the  presence  of  a  soluble  aluminium  compound,  as 
^several  other  mineral  additions  produce  a  somewhat  similar  reaction. 


STARCH   AND    ITS    ISOMERIDES. 

dish-brown  colouration  will  be  produced  if  copper  is  present.  The 
amount  of  copper  may  be  estimated  by  moistening  100  grm.  of  the 
bread  with  sulphuric  acid,  igniting  and  estimating  the  metal  in  the  ash. 

Very  minute  proportions  of  copper  have  been  stated  to  exist  normally 
in  wheat-ash. 

Plaster  of  Paris  is  readily  separated  from  flour  by  treatment  with 
chloroform. 

Ergot  in  Flour. — The  use  of  mouldy  wheat  in  manufacturing  flour 
may  often  be  detected  by  moistening  the  sample  and  keeping  it  in  a 
tightly  closed  vessel  for  some  hours  at  about  30°,  when  any  mouldy 
taint  can  readily  be  detected. 

To  test  for  ergot  or  any  fungus,  Vogel  advises  microscopic  exam- 
ination of  the  flour  after  staining  with  aniline  violet.  Starch  gran- 
ules that  have  been  injured  by  the  fungus  acquire  an  intense  violet  tint, 
sound  granules  remain  relatively  colourless.  Griiber  heats  a  little 
of  the  moistened  flour  on  a  microscopic  slide  to  the  b.  p.  and  examines 
with  a  power  of  120  diameters  when  cold.  Ergot  may  be  identified 
by  its  high  refracting  power,  furrows  and  colour — deep  violet  on  the 
edge,  greenish-yellow  inside. 

Chemical  Tests. — 20  grm.  of  flour  are  exhausted  with  boiling 
alcohol  in  a  Soxhlet  or  other  suitable  apparatus  until  the  last  extract 
is  colourless,  and  i  c.c.  of  cold  dilute  sulphuric  acid  added.  In  the 
presence  of  ergot  the  solution  will  be  red  and  when  examined  by  the 
spectroscope  in  dilute  solution  will  show  two  absorption  bands:  one 
in  the  green  near  E,  and  a  broader  and  stronger  band  in  the  blue 
between  F  and  G.  On  diluting  the  alcohol  with  a  large  volume  of 
water  the  colour  may  be  extracted  from  separate  portions  by  ether, 
amyl  alcohol,  chloroform  and  benzene. 

10  grm.  of  flour  are  digested  for  half  an  hour  with  20  c.c.  of  ether 
and  10  drops  of  dilute  sulphuric  acid  (1:5).  The  liquid  is  filtered 
and  the  residue  washed  with  ether  until  15  c.c.  of  filtrate  are  obtained. 
This  is  shaken  with  sodium  hydrogen  carbonate  which  takes  on  a  deep 
violet  colour  if  ergot  be  present,  whereas  the  chlorophyl  remains  in  the 
ether. 

BREAD. 

Bread  is  the  flour  of  wheat  made  into  a  paste  by  kneading  with 
water  and  permeated  with  carbon  dioxide,  produced  as  a  rule  by 
fermentation  with  yeast,  but  also  by  other  methods.  On  baking  the 


BREAD. 


459 


gluten  swells  and  retards  the  escape  of  the  gas  which  expands  little 
cells  and  gives  to  bread  the  familiar  light,  spongy  appearance.  The 
outside  of  the  loaf  becomes  as  hot  as  210°,  and  is  to  some  extent  cara- 
melised; the  inside  crumb  is  seldom  raised  much  above  100°.  The 
amount  of  water  in  a  loaf  varies  from  30  to  40%  on  the  average,  as 
shown  by  the  following  analyses  of  wheaten  bread  collected  by  Konig 
and  taken  from  Wynter  Blythe. 


Minimum 

Maximum 

Mean  for 
fine  bread 

Mean  for 
coarse 
bread 

Water                                                   '        26  39 

47   QO 

?8.  si 

41  .  02 

Nitrogenous  substances  4.81 
Fat     .              o  10 

8.69 

I    OO       | 

6.82 
0.77 

6.23 

O.  22 

Sugar  .  .        o  82 

4-47 

2  .  37 

2.  13 

Carbohydrates    38  93 

62   08 

40-07 

48.69 

Fibre  °  •  33 

y 
o.oo 

0.18 

O.62 

Ash  0.84 

1  .40      ' 

I    18 

I  .09 

The  moisture  depends,  among  other  conditions,  on  the  quality  and 
quantity  of  the  gluten  and  the  size  and  shape  of  the  loaf. 

The  ash  of  a  wheaten  flour  loaf  seldom  exceeds  1.5%;  beyond  2% 
would  indicate  mineral  adulteration.  A  small  quantity  of  common 
salt  is  added  to  bread  during  manufacture.  tj>% 

Bread  is  relatively  seldom  adulterated.  To  test  for  alum,  bread  is 
moistened  with  water  and  then  with  alkaline  logwood  solution  (p.  457) ; 
if  alum  be  present  the  bread  becomes  lavender-blue  in  an  hour  or  two. 
The  crust  and  crumb  should  be  analysed  separately,  as  an  alumned 
flour  has  been  known  to  be  used  for  dusting  and  facing  the  sponge 
before  baking  it.  To  search  for  alum  in  crust  it  must  be  burnt  to  ash. 

Blythe  has  found  that  a  certain  proportion  of  alum  may  always 
be  washed  out  of  the  bread  as  alum.  100  grm.  of  bread  are  soaked  in 
water  for  about  24  hours,  the  liquid  strained  through  muslin  and  con- 
centrated in  a  platinum  dish.  A  strip  of  gelatin  is  steeped  in  a  portion 
on  overnight  and  the  logwood  test  applied  when  a  blue  is  obtained, 
if  alum  be  present,  to  the  extent  of  0.03%.  Allen  suggested  to 
to  dissolve  the  starch  by  malt  extract,  remove  soluble  carbohy- 
drates by  yeast,  acidify  with  nitric  acid,  filter,  evaporate,  ignite 
the  residue  and  precipitate  as  phosphate  in  the  usual  way.  fl 

Alum  is  estimated  by  the  Dupre-Wanklyn  method  as  follows:  100 
grm.  of  bread  are  ashed  in  a  platinum  dish,  boiled  with  3  c.c.  of 


460  STARCH   AND    ITS    ISOMERIDES. 

strong  hydrochloric  acid  and  30  c.c.  of  water;  filtered  and  the  pre- 
cipitate (chiefly  silica  and  unburnt  carbon)  washed,  dried,  burnt  and 
weighed.  5  c.c.  of  ammonia  are  added  and  the  calcium,  magnesium, 
iron  and  aluminum  phosphates  precipitated.  The  liquid  is  strongly 
acidified  with  acetic  acid,  boiled  and  filtered  and  the  insoluble  phos- 
phates remaining  are  washed  and  dried  and  weighed.  The  pre- 
cipitate is  redissolved  and  the  iron  estimated  colourimetrically  with 
ammonium  sulphide,  calculated  as  phosphate  and  subtracted  from 
the  total  to  give  the  weight  of  the  aluminum  phosphate. 

An  alternative  method  consists  in  burning  the  ash,  boiling  with 
hydrochloric  acid  and  filtering  as  above.  The  filtered  solution 
is  again  boiled  and  poured  hot  into  a  very  strong  solution  of  sodium 
hydroxide,  the  mixture  being  again  boiled  and  filtered  while  hot. 
A  little  disodium  hydrogen  phosphate  is  added  to  the  filtrate  which 
is  then  slightly  acidified  with  hydrochloric  acid  and  finally  made  just 
alkaline  by  ammonia.  The  precipitate  of  aluminum  is  filtered, 
washed,  ignited  and  weighed. 

Flour  normally  contains  a  small  proportion  of  aluminum  in  the 
form  of  silicate.  It  is  customary,  therefore,  to  determine  the  silica, 
subtract  it  from  the  amount  of  alum  calculated  from  the  aluminum 
phosphate  found  and  multiply  the  remainder  by  3.87  or  3.71  to  give 
approximately  the  potassium  or  ammonium  alum,  respectively.  (For 
further  information  on  this  question  see  Blythe's  "Foods.") 

The  use  of  porcelain  vessels  is  to  be  avoided  throughout  the  process 
and  care  taken  that  the  alkaline  liquids  are  not  heated  in  glass  and 
that  the  sodium  hydroxide  used  is  scrupulously  free  from  alumina. 

The  presence  of  plaster  of  Paris  in  bread  is  recognised  by  the  high 
total  ash  and  the  high  proportion  of  calcium  contained  in  it.  The 
sulphates  of  the  ash  do  not  afford  a  means  of  accurately  determining 
the  amount  of  plaster  present,  as  proteins  furnish  a  notable  quantity  of 
sulphates  on  igniting  the  cereals.  On  the  other  hand,  only  traces  of 
sulphates  exist  ready  formed  in  the  cereals,  and  hence  the  estimation  of 
them  in  the  unignited  bread  affords  a  means  of  measuring  the  plaster 
present.  This  method,  though  theoretically  perfect,  presents  some 
difficulties  in  practice,  owing  to  the  difficulty  of  obtaining  a  solution  of 
the  sulphates  fit  for  precipitation  with  barium  chloride.  The  best  way 
is  to  soak  12.20  grm.  of  the  bread  for  some  days  in  1200  c.c.  of  cold 
distilled  water  till  mould  commences  to  form  on  the  surface  of  the 
liquid.  The  solution  is  strained  through  coarse  muslin,  and  the 


MIXED    FLOURS.  461 

filtrate  treated  with  20  c.c.  of  phenol  distilled  over  a  small  quantity  of 
lime.  The  whole  is  then  raised  to  the  b.  p.  and  filtered  through  paper. 
1000  c.c.  of  the  filtrate  are  then  slightly  acidulated  with  hydrochloric 
acid,  and  precipitated  in  the  cold  by  barium  chloride.  237  parts  of 
barium  sulphate  represent  136  of  plaster  of  Paris. 

Detection  of  Bleaching  Agents  in  Flour. — During  the  last  few 
years  there  has  been  a  widespread  adoption  of  bleaching  processes 
in  the  preparation  of  flour.  Inasmuch  as  most  bakers  are  accustomed 
to  look  upon  the  colour  as  the  most  reliable  criterion  of  flour,  the 
practice  makes  an  inferior  flour  resemble  a  superior  one.  Many  of 
the  processes  (those  of  Alsop  and  Andrews)  make  use  of  small  quanti- 
ties of  nitrogen  oxides  in  air  to  bleach  the  flour  with  or  without  ozone. 
Others  involve  the  use  of  chlorine  or  bromine.  In  all  cases  of 
bleaching  the  agents  probably  form  additive  products  with  one  or 
more  of  the  constituents  of  the  flour.  The  most  delicate  test  for  nitrites 
is  the  Griess-Ilosvay  method  (see  page  241). 

The  following  scheme  will  be  found  useful  in  testing  flours  for 
bleaching:  20  to  30  grm.  of  flour  are  extracted  with  an  equal 
number  of  c.c.  of  benzene  and  the  solution  filtered  into  a  porcelain  dish. 
If  colourless  or  nearly  so,  bleaching  may  be  suspected.  The  solution 
is  evaporated  to  dry  ness  and  the  colour  of  the  oily  residue  observed. 
An  orange-red  often  indicates  nitric  oxide,  whilst  chlorine  or  bromine 
give  a  faint  yellow  or  nearly  white  residue.  An  ignited  bead  of  copper 
oxide  is  moistened  in  the  oil  residue  and  held  in  the  bunsen  flame  when 
a  bright  green  tinge  confirms  chlorine  or  bromine.  20  c.c.  of  water 
are  added  to  the  exhausted  flour  residue  and  i  c.c.  of  the  Griess- 
Ilosvay  reagent  added,  when  a  very  characteristic  pink  results  if 
nitrous  bleaching  agents  have  been  employed.  The  occasional  use 
of  nitrosyl  chloride  as  a  bleaching  agent  makes  both  tests  desirable  on 
the  same  sample. 

MIXED  FLOURS. 

The'  addition  of  other  flours  to  wheaten  flour  is  somewhat  uncommon, 
but  may  occur.  The  detection  of  such  addition  is  a  matter  of  consider- 
able difficulty  and  requires  patient  examination  under  the  microscope. 
Recent  investigations,  particularly  those  of  Bigelow  and  Sweetser, 
Kraemer  and  Vogel  have  established  certain  data  on  which  tests  may 
be  based. 

Vogel  advises  extraction  with   70%  alcohol  containing  5%  hydro- 


462  STARCH   AND    ITS    ISOMERIDES. 

chloric  acid.  Pure  wheat  or  rye  flour  give  a  colourless  extract,  with 
barley  or  oats  a  pale  yellow  extract,  with  pea  flour  an  orange-yellow 
extract  is  obtained,  mildewed  wheat  gives  a  purple-red  and  ergotised 
wheat  a  blood-red  colouration. 

Much  may  be  ascertained  from  the  gluten  which  is  dark  and  vis- 
cous when  rye  flour  is  present,  dark,  non-viscous  and  dirty  reddish- 
brown  with  barley,  dark  yellow  with  oats,  yellowish  and  non-elastic 
with  maize  and  varies  from  a  greyish-red  to  green  in  the  case  of  legu- 
minous flours,  such  as  bean  or  pea. 

Leguminous  starches  give  more  ash  than  wheat  flours;  this  ash  is 
deliquescent,  high  in  chlorides  and  turns  turmeric  paper  brown. 
To  detect  legumin,  the  gluten  is  washed  from  a  sample  of  the  flour  in 
the  usual  manner  and  the  nitrate  made  alkaline  with  ammonia. 
It  is  allowed  to  stand  overnight,  the  clear  liquid  decanted  and  the  le- 
gumin precipitated  by  a  dilute  mineral  acid.  It  may  be  collected, 
dried  and  weighed.  According  to  Lemenant  des  Chenais,  0.9  grm. 
of  legumin  may  be  taken  as  indicating  the  mixture  of  5%  of  legu- 
minous flour. 

A  method  of  detecting  potato  flour  in  wheat  is  based  on  the  resist- 
ance to  destruction  of  the  outer  membrane  shown  by  wheat  flours. 
The  sample  is  rubbed  in  a  mortar  with  water  to  a  stiff  paste,  which  is 
then  diluted  and  filtered.  The  filtrate  tested  with  a  drop  of  dilute 
iodine  solution  gives  a  deep  blue  with  potato  starch  and  a  yellow  or 
orange  with  pure  wheat  flour.  ' 

Maize. — Kraemer  states  that  5%  of  maize  in  wheat  flour  may  be 
detected  by  mixing  i  grm.  of  the  sample  with  15  c.c.  of  glycerol  and 
heating  to  boiling  for  a  few  minutes.  Maize  is  indicated  by  the  well- 
known  odour  of  pop-corn. 

A  small  quantity  of  the  flour  is  treated  with  10  c.c.  of  1.8%  potas- 
sium hydroxide  for  2  minutes  in  a  test-tube  and  then  nearly  neutralised 
with  hydrochloric  acid;  wheat  starch  is  gelatinised,  maize  remains 
intact. 

Sawdust. — Le  Roy  (Ann.  Chim.  anal.,  1899,  4,  212)  suggests 
the  following  test:  i  grm.  phloroglucinol  is  dissolved  in  15  c.c. 
90  to  95%  alcohol  and  10  c.c.  of  syrupy  phosphoric  acid,  i  to  2  c.c.  of 
this  reagent  are  rubbed  with  a  little  of  the  sample  in  a  porcelain  dish, 
when  sawdust  assumes  at  first  a  rose  and  gradually  a  carmine  tint. 
Pagamini  (Chem.  Centr.,  1905,  i,  695-696)  moistens  the  flour  spread 
in  a  thin  layer  first  with  a  0.2%  aqueous  solution  of  paraphenylenedia- 


CEREALS .  463 

mine  and  then  with  acetic  acid.  The  sawdust  fragments  are  at  once 
coloured  orange-yellow. 

To  detect  rice  flour,  Gastine  (Comptes.  rend.,  1906,  142,  1207) 
advises  staining  with  aniline  blue  or  green,  which  shows  up  the  hilum 
of  the  minute  rice-starch  granule  as  a  reddish  coloured  point. 

Other  Cereals.     (For  analyses  see  page  452.) 

Maize — Zea  Mais. — Maize  or  Indian  corn,  though  coming  origin- 
ally from  America,  has  been  largely  cultivated  in  other  countries.  It  is 
extensively  used  in  the  United  States  and  its  use  is  on  the  increase  in 
Europe  where  it  has  been  somewhat  difficult  to  overcome  the  prejudice 
against  it  as  it  was  first  introduced  as  a  food  for  lower  animals. 
Corn  starch  is  frequently  met  with  in  foods  for  invalids  and  infants. 
Maize  is  especially  rich  in  fats,  containing  5.2%  according  to  the 
United  States  Department  of  Agriculture,  and,  roughly,  twice  as  much 
oil  as  in  wheat. 

Oats — Species  of  Avena. — Oats  are  grown  in  northern  regions 
throughout  the  world.  They  contain  about  6%  of  fat  and  a  high  per- 
centage of  mineral  matter.  Oatmeal  preparations  are  very  largely 
used  as  breakfast  foods  and  accordingly  are  found  adulterated  with 
other  cereals,  particularly  barley.  The  admixture  is  only  to  be  de- 
tected by  microscopical  investigation. 

Barley— Species  of  Hordeum.— Barley  is  chiefly  grown  for  the 
purpose  of  making  malt.  Both  barley  meal  and  "pearl  barley,"  i.  e., 
the  grain  deprived  of  its  outer  coating  and  rounded  by  attrition,  are 
used  as  foods,  and  barley  meal  is  frequently  used  as  an  adulterant  in 
other  foods. 

Rye — Secale  cereale. — Rye  bread  has  now  almost  fallen  out  of  use 
in  England,  but  it  is  the  staple  bread  of  the  northern  European 
nations.  The  fat  is  small  in  quantity  and  largely  olein.  The  grain  is 
particularly  liable  to  become  affected  by  ergot. 

Rice — Oryza  sativa. — Rice  is  the  main  food  of  a  third  of  the  human 
race.  The  term  is  applied  to  the  seed  separated  from  the  hulls.  It 
contains  about  7%  of  proteins  and  i%  of  fat  and  is  readily  digestible 
when  cooked. 

Bananas. — These  combine  the  sweet  qualities  of  a  fruit  with  the 
nourishing  properties  of  a  vegetable,  they  are  rich  in  sugar  and  starch 
and  contain  a  fair  quantity  of  proteins.  A  banana  flour  is  made  by 
drying  the  ripe  fruit;  this  contains  4%  proteins,  0.5%  fat,  80%  carbo- 
hydrates, 2.5%  ash. 


464 


STARCH   AND    ITS    ISOMERIDES. 


Of  late  a  number  of  wheat  and  oat  products  have  been  placed  on 
the  market,  particularly  in  the  United  States,  as  breakfast  foods.  These 
are  either  uncooked,  partially  cooked  by  steaming  and  drying  or  cooked* 
and  malted.  The  following  analyses  of  some  of  these  were  made  by 
Harcourt  (J.Soc.  Chem.  Ind.,  1907,  26,  240-243): 

PERCENTAGE  COMPOSITION  OF  SOME  BREAKFAST  FOODS. 


•SB'S 

<*!£ 
525  11 

Water 

Crude 
protein 

Crude 
fa< 

6* 

I? 

c3T3 
U£ 

Crude 
fibre 

Ash 

&{ 

£S 

E?2 

(U      . 

«! 

Granulated  oats  

12 

7.71; 

12.  2Q 

6.65 

71.71 

(1.50) 

.60 

4    28"? 

Rolled  oats  

JO 

8.55 

11.83 

6.61 

71.  3C 

(1-25) 

.66 

4    238 

^^heat  farina 

8 

10.  63 

o-  70 

I  .OC 

78    23 

(062) 

^7 

<>  c76 

^^heat  germ 

i 

8     70 

10.07 

2   70 

76   77 

d  lO 

08 

^5-o/u 

Rolled  wheat  

2 

IO  41 

w-y/ 
8.77 

1  .00 

77.  22 

(2  o?) 

7O 

3  860 

Flaked  barley  

4 

IO    ?O 

9.71 

I  -43 

76.8l 

/      5\ 

(2.07) 

47 

3.    8^4 

Cornmeal  

2 

0-  76 

6.00 

1  .  26 

81.40 

fo.sa) 

O    ^O 

3    87O 

Orange  meat 

8  66 

97O 

I    31 

78   43 

>    j  < 

Tl  QtC) 

Force  

3 

9.06 

10.  14 

i.  <;i 

76.88 

(i.80 

2.41 

•vuy 
3  886 

Norka 

7. 

7    "*8 

14    33 

r    r<r 

60  oi 

d  84) 

2    83 

Malta  Vita  

2 

8    23. 

o  88 

I    3O 

78    27 

^•°O 
2    2^ 

Grape  Nuts  

•2 

«J.  *J 

7.08 

1  1  .  40 

O  O4 

78.78 

•*•  -^J 
I    71 

•y*5 

Canada  Flakes  

2 

/  •*- 
8.07 

IO.84. 

*"y*j 

1.18 

76    22 

A  •  1  *• 
2    7O 

•yy:> 
3  874 

Shredded  Wheat  
Rice  Flakes 

2 
I 

9.41 

12    2O 

"•53 

724 

0.85 
o  08 

76.51 
80    O4 

Co  cc) 

1.70 

o  •°/'t 
3.916 

.  ^q. 

W-JO/ 

u-oo 

.710 

PAPER  AND  PAPER-MAKING 
MATERIALS. 


BY  R.  W.  SINDALL,  F.  C.  S. 

During  the  last  few  years  the  systematic  application  of  chemical  and 
microscopical  analysis  in  the  paper  trade  has  become  a  matter  of  con- 
siderable importance.  Prior  to  1860  the  manufacture  of  paper  had 
proceeded  along  comparatively  simple  lines,  the  only  raw  material 
used  in  any  quantity  being  rags,  which  required  but  little  chemical 
treatment  for  conversion  into  paper.  The  high  percentage  of  cellulose 
in  cotton  or  linen  rendered  any  drastic  treatment  unnecessary. 

The  wider  application  of  chemical  analysis  in  the  paper  trade  can 
be  traced  to  a  number  of  causes,  amongst  which  may  be  mentioned  the 
introduction  of  new  paper-making  materials,  such  as  esparto,  straw  and 
wood,  requiring  more  severe  treatment  than  the  simple  methods  in 
vogue  for  the  purification  of  rags.  The  increasing  use  of  mineral 
substances,  such  as  china  clay  and  pearl  hardening,  and  the  question 
of  adulteration  by  means  of  inferior  fibres,  together  with  a  much  greater 
variety  in  the  classes  of  papers  and  allied  products  manufactured,  widens 
the  field  of  technical  analysis.  The  lack  of  standards  of  quality  and 
the  importance  of  a  study  of  the  nature  of  chemical  residues  and  fibrous 
ingredients  as  influencing  the  durability  of  the  paper  are  now  matters 
of  common  knowledge. 

The  methods  of  analysis  peculiar  to  paper-making  may  be  classified, 
most  conveniently  under  the  heads,  (i)  the  manufacturing  process;  (2) 
the  finished  paper. 

The  process  of  the  manufacture  of  paper  requires: 

1.  Some  analytical  methods  which  are  of  common  application  to  all 
manufacturing  industries. 

2.  Certain  special  methods  of  analysis  peculiar  to  the  paper  trade. 
The  former  need  only  be  mentioned  under  suitable  headings  and  the 

methods  of  analysis  must  be  sought  for  in  the  proper  text-books. 
The  special  methods  required  for  paper  analysis  will  be  described  at 
greater  length. 

VOL.  1—30  465 


466  PAPER   AND    PAPER-MAKING    MATERIALS. 

In  common  with  other  industries,  the  efficient  management  of  the 
paper-mill  requires  a  systematic  analysis  of  fuel,  and  other  measure- 
ments usually  applied  in  the  production  of  steam  for  heating  purposes 
and  motive  power. 

The  water  supply  is  a  question  of  paramount  importance  not 
only  in  regard  to  its  suitability  for  steam  boiler  purposes,  but  more  par- 
ticularly in  regard  to  its  cleanliness  and  purity  of  colour  for  the  manu- 
facture of  paper.  The  quantity  of  water  required  per  ton  of  paper 
ranges  from  5000  gallons  in  the  case  of  cheap  newspapers  to  70,000 
gallons  per  ton  in  the  case  of  high-class  rag  papers.  This  difference, 
however,  merely  concerns  the  paper-mill,  because  the  wood  pulp  util- 
ised in  the  manufacture  of  newspaper  has  already  been  thoroughly 
washed  before  reaching  the  paper-mill. 

The  chemicals  employed  for  the  conversion  of  esparto,  straw  and 
other  fibres  into  paper,  pulp  are  lime,  crude  sodium  carbonate  and 
crude  sodium  hydroxide.  The  sodium  hydroxide  is  recovered  by 
evaporation  in  a  vacuum  multiple  effect  apparatus  and  subsequent 
incineration  of  the  concentrated  mass,  resulting  in  the  formation  of  a 
crude  carbonate.  These  materials  are  examined  by  the  ordinary 
analytical  methods. 

The  boiled  pulp  is  treated  with  bleaching  powder  or  with  chlorine 
produced  by  an  electrolytic  process.  The  traces  of  bleach  are  occa- 
sionally removed  by  the  use  of  an  "antichlor,"  such  as  sodium  hypo- 
chlorite,  sulphurous  acid  and  calcium  hydrogen  sulphites  (bisulphites) . 
The  materials  used  for  sizing  the  paper  are  glue,  gelatin,  casein,  starch, 
rosin,  rosin  size  and  sundry  mineral  salts,  to  all  of  which  the  usual 
methods  of  analysis  are  applicable.  Among  the  mineral  substances 
used  as  ingredients  of  paper  are  calcium  sulphate  in  its  commercial 
forms,  china  clay,  barytes,  satin  white  (a  mixture  of  calcium  sulphate 
and  precipitated  alumina),  asbestine,  and  French  chalk. 

Many  of  the  common  pigments,  such  as  ultramarine,  Prussian  blue, 
smalts,  ochre,  as  well  as  organic  colouring  matters  are  used  in  the  manu- 
facture of  paper  and  these  may  be  examined  by  ordinary  methods. 

THE  TESTING  OF  PAPER. 

The  complete  examination  of  a  sheet  of  paper  requires  the  measure- 
ment of  its  physical  properties,  the  determination  of  the  fibrous 
constituents  and  of  other  ingredients. 


PAPER.  467 

Physical  Properties. 

Weight.— The  " substance"  of  a  paper  is  expressed  in  terms  of  the 
weight  of  a  ream  of  sheets  of  given  area.  A  ream  may  contain  480,  500 
or  516  sheets,  according  to  the  class  of  paper,  high-class  papers  being 
reckoned  as  containing  480  sheets  while  cheaper  papers  are  calculated 
for  516  sheets  per  ream.  Many  papers  are  cut  to  standard  sizes  hav- 
ing certain  technical  names,  of  which  the  following  may  be  quoted  as 
examples,  the  dimensions  being  in  inches: 


Double  Crown, 

30 

X    2O 

Demy, 

22 

•5  x  17-5 

Foolscap, 

17 

x  13-5 

Imperial, 

30 

X    22 

Post, 

21 

x  16.5 

Royal, 

24 

x  19 

The  description  of  a  high-class  paper  as  28  pounds  Double  Crown 
means  that  a  ream  of  480  sheets,  each  measuring  20  x  30  ins.,  would 
weigh  28  pounds. 

The  weight  of  a  paper  can  be 
measured  by  means  of  Leunig's 
paper  scales,  a  full-size  sheet  being 
placed  in  the  pan  of  the  scales  and 
the  weight  of  the  ream  obtained 
by  a  direct  reading  on  the  scale. 

The  weight  can  also  be  ascer- 
tained by  weighing  on  a  delicate 
balance  a  small  piece  of  known 
area  and  calculating  the  weight  of 
a  ream  by  simple  proportion.  The 
simpler  expression  of  the  weight  of 
paper  in  terms  of  grms.  per  square 
meter  or  ounces  per  1000  square 
ins.  has  not  come  into  general  use.  'IG'  7*.-Leunig's  paper  scales 

Thickness. — This  is  measured  by  means  of  a  micrometer,  special 
forms  of  which  have  been  made  for  use  in  the  paper  trade.  The  thick- 
ness is  expressed  in  inches  or  millimeters  and  sometimes  in  terms  of 
the  thickness  of  a  ream. 

Strength. — The  strength  of  a  paper  may  be  measured  in  terms  of 


468 


PAPER   AND    PAPER-MAKING    MATERIALS. 


tensile  strain — that  is,  the  weight  necessary  to  fracture  a  strip  of  given 
width — or  in  terms  of  bursting  strain — that  is,  the  number  of  pounds 
per  square  inch  required  to  burst  a  sheet  of  paper  rigidly  fixed 
between  suitable  clamps. 

Tensile  Strain. — There  are  several  machines  for  determining  the 
breaking  weight  of  a  strip  of  paper,  in  all  of  which  the  strip,  cut  to 


FIG.  73 — Leunig's  paper  testing  machine 

any  convenient  length  and  width,  is  fixed  between  clamps  in  a  hori- 
zontal or  vertical  position,  the  tension  being  applied  either  by 
means  of  a  weight  or  a  spring.  The  machines  are  constructed  to  re- 
cord the  breaking  weight  at  the  moment  of  fracture,  and  also  the 
amount  of  elongation  produced  in  the  paper  while  the  tension  is  ap- 
plied. The  Schopper  testing  machine,  in  which  a  strip  25  mm.  wide 


PAPER.  469 

and  180  mm.  long  is  suspended  vertically  between  the  clamps  and 
in  which  the  tension  is  applied  by  means  of  a  weight,  is  regarded  as 
the  standard  instrument.  With  the  Marshall  paper  testing  machine, 
which  is  much  used  in  England,  the  width  of  the  strip  may  be  from 
0.25  in.  to  2  in.,  and  the  length  from  2  to  12  in.,  the  paper  being  fixed 
in  a  horizontal  position  and  the  tension  obtained  by  means  of  a  spring. 
Machine  and  Cross  Directions. — In  ordinary  machine-made  papers 
the  strength  of  the  paper  will  differ  according  to  the  position  of  the  strip. 
The  paper  has  a  maximum  strength  in  what  is  known  as  the  "machine 
direction"  and  a  minimum  strength  in  what  is  known  as  the  "cross 
direction."  These  terms  are  derived  from  the  conditions  of  manufac- 
ture. The  paper  is  formed  by  the  felting  together  of  minute  fibres 
of  pulp  on  the  wire  cloth  of  the  machine  travelling  rapidly  forward 
in  a  horizontal  position.  A  strip  cut  from  the  sheet  of  paper  along  a 


FIG.  74. — Marshall's  paper  testing  machine. 

line  parallel  with  the  direction  in  which  the  wet  sheet  of  paper  has  been 
travelling  on  the  machine  is  said  to  be  cut  from  the  "machine"  direc- 
tion. •  In  the  same  way  a  strip  cut  at  right  angles  to  this  is  known  as  the 
"cross  "  direction. 

The  simplest  method  of  determining  exactly  the  machine  direction 
of  a  sheet  of  paper  is  to  cut  a  circular  piece  from  the  sheet,  dampen 
one  side  by  momentary  contact  with  water,  and  then  place  the  sample 
on  the  back  of  the  hand.  The  damp  paper  will  immediately  curl  up 
into  a  cylindrical  form,  the  axis  of  the  cylinder  being  parallel  with  the 
machine  direction  of  the  paper. 

It  is  usual  to  make  5  or  10  tests  for  strength  in  the  machine  direction 
and  a  similar  number  in  the  cross  direction,  the  mean  of  the  figures 
being  taken  as  the  strength  of  the  paper.  It  is  obviously  important 
to  make  a  record  of  the  strength  in  both  directions. 

Breaking  Length. — In  the  absence  of  any  definite  standards  for 
the  length  and  width  of  the  strip  it  is  convenient  to  express  the  strength 


470 


PAPER    AND    PAPER-MAKING    MATERIALS. 


of  a  paper  in  terms  of  its  breaking  length,  i.  e.,  the  length  of  strip 
which,  if  suspended,  would  break  of  its  own  weight.  This  factor  is 
calculated  by  the  formula: 

w      W 

T=17 

in  which  w  =  weight  of  test  strip. 

1  =  length  of  test  strip. 
W-=  breaking  weight  by  experiment. 
L  =  breaking  length  of  paper. 

Elasticity. — The  elongation  of  a  strip  of  paper  produced  by  sub- 
mitting the  paper  to  tension  is  an  important  indication  of  its  wearing 
qualities.  The  "stretch,"  as  it  is  called,  is  measured  simultaneously 
with  the  breaking  weight,  and  the  result  is  expressed  in  terms  of  the 
percentage  of  elongation,  i.  e.,  the  stretch  per  100  units  of  length. 

The  word  stretch,  is  frequently  applied  to  the  expansion  of  a  paper, 
such  as  a  lithographic  printing  paper,  when  wetted  for  printing.  The 
term  expansion  would  be  preferable  in  the  latter  case  and  the  two 
terms  must  not  be  confused. 


FIG.  75. — Marshall's  paper  testing  machine  (secti  n). 


Resistance  to  Folding. — The  capacity  of  a  paper  for  resisting  wear 
and  tear,  folding  and  crumpling  is  of  considerable  importance  in  high- 
class  papers  intended  to  be  frequently  handled.  The  methods  in 
common  use  are  more  or  less  empirical,  but  nevertheless  serve  the  pur- 
pose  of  comparison. 

The  loss  due  to  folding  may  be  measured  by  taking  strips  in  the  two 
directions  of  the  paper,  folding  them  backwards  and  forwards  repeat- 
edly, either  by  hand  or  by  using  a  special  appliance  constructed  for 
this  purpose.  The  strip  is  then  tested  in  the  usual  way  and  the  per- 
centage loss  of  strength  calculated. 


PAPER.  471 

The  resistance  to  crumpling  may  be  measured  by  crumpling  a 
sheet  of  paper  between  the  fingers  into  a  small  ball,  which  is  then 
smoothed  out  again  and  the  sheet  examined  for  pin-holes  produced 
by  the  friction.  A  record  is  made  of  the  number  of  foldings  made 
and  the  number  of  holes  produced  at  intervals. 

An  elaborate  machine  has  been  devised  for  measuring  this  resist- 
ance to  crumpling  in  order  to  eliminate  errors  which  must  occur  with 
empirical  methods. 


FIG.  76. — Muller's  "Bursting  Strain  "  paper  testing  machine. 

Bursting  Strain. — There  are  several  machines  by  means  of  which 
the  so-called  bursting  strain  of  paper  is  determined.  These  machines 
are  based  upon  the  application  of  pressure  to  the  surface  of  a  sheet  of 
paper  fixed  rigidly  between  horizontal  clamps,  the  pressure  required 
to  burst  the  paper  being  registered  on  an  ordinary  gauge  in  terms  of 
pounds  per  square  inch.  Machines  of  this  type  are  very  useful  for  com- 
parative results  since  no  special  precautions  are  necessary  in  adjusting 
the  paper,  whereas  in  the  case  of  machines  for  determining  tensile 
strain  great  care  is  necessary  in  proper  adjustment,  but  no  measure- 


47 2  PAPER   AND    PAPER-MAKING    MATERIALS. 

ments  of  the  difference  in  strength  between  the  machine  and  cross 
directions  of  paper  or  of  elongation  under  tension  are  obtained. 

Sizing  Qualities. — The  ink  resisting  property  of  a  paper  may  be 
measured  by  several  methods  more  or  less  accurate. 

1.  The  Use  of  Strong  Ink. — Lines  are  drawn  on  the  paper  with 
a  soft  quill  pen  and  a  note  made  as  to  the  behaviour  of  the  ink.     With 
a  paper  poorly  sized  the  ink  quickly  penetrates. 

2.  Schluttig  and   Neumann's  Method. — The   paper   is  fixed   on  a 
slip  of  wood  at  an  angle  of  60°.     A  solution  of  ferric  chloride  is  al- 
lowed to  flow  down  on  the  surface  of  the  paper  and  left  for  1 5  or  20 
minutes.     The  paper  is  then  reversed  and  a  solution  of  nut-gall  tannin 
allowed  to  flow  on  the  other  side  of  the  paper  in  a  direction  at  right 
angles  to  that  previously  used.     Usually  3  lines  of  solution  are  pro- 
duced   on   each   side   of   the   paper.     At   the  points  of  intersection 
chemical  reaction,  more  or  less  definite,  between  the  tannin  and  iron 
salt  sets  in  with  the  formation  of  a  black  stain.     With  well-sized 
papers  the  effect  may  be  very  slight. 

3.  Leonhardi's  Method. — One  drop  of  a  1.5%  ferric  chloride  solu- 
tion is  allowed  to  fall  on  the  surface  of  the  paper  and  to  remain  for  a 
number  of  seconds  equivalent  to  the  weight  of  the  paper  in  grms.  per 
square -metre.     Excess  of  solution  is  then  dried  off  with  blotting-paper 
and  the  back  of  the  sheet  moistened  with  a  i%  solution  of  tannin  and 
a  note  made  of  the  effect  produced. 

Comparative  methods  of  this  description  allow  of  an  approximate 
classification  as  follows: 

1.  Unsized,  Drops  penetrate  quickly. 

2.  Moderately  sized,  Drops  require  one  minute  for  penetration. 

3.  Well  sized,  Drops  require  3  minutes. 

4.  Very  well  sized,  Drops  require  5  minutes  or  more. 

5.  Extremely  well  sized.  No  results. 

Absorbency. — This  property  of  paper,  viz.,  its  power  to  absorb  water 
and  other  liquids  is  chiefly  of  importance  for  blottings,  filtering  paper 
and  copying  paper.  The  papers  are  tested  by  determining  the  effect 
produced  by  suspending  strips  vertically  with  the  lower  end  dipping 
into  distilled  water,  ink  or  similar  solutions.  A  measurement  is  made 
of  the  rate  at  which  the  solution  is  drawn  up  by  capillary  attraction 
and  of  the  total  height  to  which  the  solution  rises  in  a  given  time. 

The   "zone"   test  is   useful-    particularly  for  blottings.      0.5   c.c. 


3SITY   1 


PAPER    MATERIALS. 


473 


of  ink  is  cautiously  dropped  from  a  burette  on  to  the  surface  of  the 
paper  placed  0.5  in.  below  the  burette  in  a  horizontal  position  on  the 
top  of  a  beaker.  The  blot  is  allowed  to  dry  and  it  will  be  found  that 
the  blot  consists  of  two  zones,  the  outer  one  of  which  is  practically 
impervious  to  ink  as  may  be  tested  by  passing  a  pen  across  from  the 
centre  of  the  blot  to  the  outside. 


Fibrous  Constituents  of  Paper. 

The  vegetable  fibres  commonly  employed  for  the  manufacture  of 
paper  are  cotton,  linen,  hemp,  esparto,  straw,  chemical  wood  pulp, 
mechanical  wood  pulp,  jute  and  manila  hemp.  Other  materials,  such 
as  ramie,  bamboo,  rice  straw,  aloe,  and  paper  mulberry,  are  occasion- 
ally found  in  paper  of  foreign  origin. 

The  existence  of  such  fibres  and  the  proportions  in  which  they  are 
present  is  determined  by  a  microscopic  examination.  The  fibres  are 
identified  by  their  peculiar  physical  structure,  while  the  application  of 
certain  staining  reagents  serves  to  assist  in  differentiating  between 
them,  not  only  by  a  clearer  definition  of  structure,  but  by  varying  colour 
reactions.  The  following  table  shows  the  staining  effect  produced  by 
the  reagents  generally  employed. 

COLOUR  EFFECTS  PRODUCED  BY  STAINING  REAGENTS. 


Fibres 

Iodine  solution 

Zinc  chloride- 
iodine  solution 

Magnesium 
chloride-iodine 
solution 

Cotton   linen   hemp 

Brown 

Wine-red 

Reddish-brown 

Esparto,  straw,    bamboo    cellu- 
loses                    

Grey  to 

Blue  to  violet 

Bluish-violet 

Wood  celluloses  

greyish- 
brown 
Colourless 

or  blue  to 
greyish-  violet 
Blue  to  bluish- 

Light  brown  to 

IVIanila  hemp              

Grey,  brown 

violet 
Dark  yellow  or 

red 
Yellow,  green 

Mechanical  wood  pulp,  jute  .  .  . 

Unbleached  manila,  straw  (par- 
tially boiled)             

or  yellowish 
Yellow 
Yellow 

greenish-yellow 
Yellow 
Yellow 

ish-yellow 
Yellow 
Yellow 

474  PAPER   AND    PAPER-MAKING    MATERIALS. 

THE  REAGENTS  ARE  PREPARED  AS  FOLLOWS: 


Ingredients 

Iodine  solution 

Zinc  chloride- 
iodine  solution 

Magnesium 
chloride-iodine 
solution 

Iodine 

I    I  ^   DtS 

I    O  pt 

I    O  pt 

Potassium  iodide 

2    O  ptS. 

c  .  O  DtS. 

r  .  o  DtS. 

Water  

20  o  pts. 

I  "?  .  O  DtS. 

2O.  O  pts. 

Zinc  chloride 

40  o  pts 

Magnesium  chloride  .  . 

3O.O  DtS. 

The  iodine  is  dissolved  in  water  with  the  potassium  iodide,  and  the 
solution  added  to  the  zinc  or  magnesium  chloride.  The  mixture  is 
allowed  to  stand  and  the  clear  supernatant  liquor  bottled  for  use. 

Appearance  of  Fibres  Examined  by  the  Microscope. — The 
physical  structure  of  fibres  after  they  have  been  boiled,  bleached  and 
beaten  for  the  preparation  of  paper  differs  considerably  in  many  cases 
from  that  of  the  raw  material.  That  is  to  say,  the  processes  modify  and 
lessen  the  characteristic  distinctions  which  are  usually  pronounced  in 
the  raw  fibre.  The  examination  of  papers  containing  fibres  not  com- 
monly used  is  considerably  facilitated  by  comparison  with  fibres  of 
known  origin.  The  following  is  a  brief  description  of  the  commonly 
occurring  fibres: 

Cotton  resembles  a  flat  collapsed  tube  with  occasional  spiral  twists, 
numerous  in  the  raw  material,  but  less  frequent  in  beaten  paper  pulp. 
The  cell  walls  often  striated  with  lattice-like  markings.  Central 
canal  broad.  Complete  absence  of  pores  and  knots.  Ends  of  fibres 
blunt. 

Linen  consists  of  well-shaped  cylindrical  tubes  with  narrow  cen- 
tral canal.  Ends  of  fibres  pointed.  Characteristic  knots  at  intervals 
in  the  fibre.  Walls  of- cell  marked  with  pores.  In  beaten  pulp  these 
peculiar  features  are  less  marked,  the  fibre  ends  being  usually  frayed 
out. 

Hemp  closely  resembles  linen.  Well-beaten  hemp  is  very  difficult 
to  distinguish.  Cell  walls  frequently  striated  parallel  to  length  of  fibre, 
ends  flat  or  fork-shaped.  Fibres  sometimes  flattened  out  by  the 
beating  process  will  show  structure  more  clearly. 


PAPER   MATERIALS.  475 

Esparto  fibres  are  fine,  slender,  short  cylindrical  tubes  with  tapered 
ends  and  very  small  central  canal.  Fibres  seldom  cut  or  destroyed  by 
beating.  Numerous  pear-shaped  seed  hairs  and  serrated  epidermic 
cells  serve  to  identify  esparto  and  to  distinguish  it  from  straw. 

Straw  fibres  thicker  than  esparto,  which  in  some  respects  resembles 
straw.  Central  canal  irregular  in  shape.  Walls  of  fibre  thickened  at 
intervals,  giving  appearance  of  knots.  Numerous  serrated  cells. 
Many  thin  transparent  parenchyma  cells  of  large  area.  These  latter 
are  entirely  absent  from  esparto  cellulose. 

Bamboo  fibres  are  long  slender  tubes  with  tapered  ends.  The 
pulp  contains  epidermic  cells  which  in  general  appearance  resemble 
those  of  esparto  and  straw,  but  may  be  differentiated  by  careful 
examination. 

Chemical  wood  pulp  fibres  differ  according  to  the  wood  from  which 
the  pulp  has  been  made.  Generally  speaking,  fibres  are  flat  and 
broad  and  strongly  marked  with  pores  and  pitted  vessels,  the  shape 
and  number  of  which  serve  to  identify  the  species  of  wood.  The  fibres 
from  the  coniferous  woods,  such  as  spruce  and  fir,  are  flat  ribbons 
with  characteristic  pitted  vessels  while  the  fibres  of  the  deciduous 
trees,  such  as  poplar,  birch  and  aspen,  are  more  cylindrical  in  shape  and 
the  pulp  contains  in  addition  to  the  long  fibres  a  number  of  oval-shaped 
cells  with  markings  which  vary  according  to  the  nature  of  the  wood. 

Mechanical  wood  pulp  contains  fibres  of  indefinite  structure.  The 
fibres  of  definite  shape  mixed  with  bundles  of  incompletely  separated 
fibres  and  structureless  particles  are  easily  recognised.  The  use  of 
staining  reagents  applied  to  papers  containing  mechanical  wood  pulp 
is  of  great  service  in  identification. 

Jute  strongly  resembles  hemp  or  manila,  having  knots  and  irregular 
markings.  The  most  characteristic  feature  is  the  central  canal  or 
lumen  which  varies  in  diameter,  opening  out  suddenly  in  parts  and 
closing  up  again.  Unless  completely  free  from  ligneous  matter  the 
fibres  are  found  aggregated  together  in  bundles. 

Mounting  Sample  of  Paper  for  Microscope. — 0.5  grm.  of  paper  is 
gently  heated  in  a  weak  solution  of  sodium  hydroxide  to  dissolve  out 
the  size,  well  washed  and  then  broken  into  pulp,  either  by  maceration 
in  a  mortar  or,  better  still,  by  agitation  in  a  bottle  with  a  number  of 
beads.  The  pulp  so  produced  is  washed  and  a  suitable  quantity 
placed  on  a  glass  slip,  excess  of  water  being  drained  off  by  means  of 
blotting  paper  and  one  drop  of  the  staining  reagent  added.  The 


476  PAPER   AND    PAPER-MAKING    MATERIALS. 

fibres  are  carefully  distributed  by  teasing  out  with  a  glass  rod  or  a 
microscope  needle,  and  the  cover-glass  put  on  in  the  usual  way. 

Percentages  of  Various  Fibres. — When  a  paper  contains  several 
fibres,  such  as  sulphite  and  mechanical  wood  pulps  in  a  cheap  news, 
or  esparto  and  chemical  wood  pulp  in  a  magazine  paper,  it  is  necessary 
to  determine  the  proportions  in  which  the  fibres  are  present.  This 
requires  considerable  experience  which  can  only  be  obtained  by  prac- 
tising with  known  mixtures.  The  simplest  method  of  estimating  the 
percentage  of  fibre  present  is  to  examine  4  or  5  slides,  going  carefully 
over  the  whole  of  the  pulp  on  the  slide  and  obtaining  a  "  mental  im- 
pression" of  the  proportions  in  which  the  fibres  are  present.  Some 
observers  count  the  number  of  fibres  of  each  kind  and  estimate  the 
percentage  in  this  way,  but  the  better  plan  is  to  become  familiar  with 
the  fibres  by  work  on  papers  of  known  composition  so  that  a  correct 
mental  impression  is  obtained.  The  microscopic  examination  of  paper 
in  regard  to  the  estimation  of  the  percentages  of  fibre  can  only  be 
effected  by  considerable  practice  and  cannot  be  accomplished  accord- 
ing to  any  exact  methods  of  analysis. 

Mineral  Constituents  of  Paper. — Ordinary  papers  contain  mineral 
substances  technically  described  as  loadings  or  fillers,  added  partly 
for  the  purpose  of  giving  weight  and  partly  to  improve  the  surface 
of  the  sheet  and  increase  its  opacity.  The  substances  which  may  be 
present  in  ordinary  papers  are  china  clay,  barium  sulphate  of  calcium 
sulphate  (pearl  hardening,  gypsum,  terra  alba),  magnesium  silicates 
(French  chalk,  talc,  asbestine,  agalite),  satin  white  (a  mixture  of  pre- 
cipitated alumina  and  calcium  sulphate). 

Percentage  of  Mineral  Substances  in  Paper. — A  convenient 
weight  is  ignited  in  an  ordinary  crucible  until  there  is  no  further  loss 
of  weight.  The  ash  is  weighed  and  the  percentage  calculated. 
Special  appliances  have  been  devised  for  making  ash  determinations, 
but  these  offer  no  particular  advantages. 

Nature  of  Ash  in  Papers. — In  addition  to  the  mineral  substances 
noted  papers  may  contain  pigments,  such  as  ultramarine  lead  chro- 
mate,  iron  oxides  and  other  inorganic  bodies,  according  to  the  quality 
of  the  paper  and  its  special  use.  All  papers  contain  some  ash,  which, 
when  in  small  quantity  need  not  be  regarded  as  evidence  of  added 
mineral  matter,  as  it  may  be  derived  from,  the  fibrous  material,  from 
the  alum  used  for  sizing  or  from  hard  water. 

The  complete  examination  of  the  ash  involves  an  analysis  of  a  suffi- 


PAPER    MATERIALS.  477 

cient  quantity  by  ordinary  methods  which  therefore  need  not  be  given 
in  detail  here. 

Sizing  Constituents  of  Paper. — A  large  number  of  organic 
substances  have  been  used  for  rendering  paper  more  or  less  im- 
pervious to  moisture,  many  of  them  only  experimentally.  The  com- 
mon sizing  agents  are  gelatin,  starch  and  rosin,  while  casein,  viscose 
and  algin  find  a  limited  use. 

Gelatin  in  paper  is  easily  extracted  by  gently  heating  a  small 
sample  in  water.  The  extract,  cooled  and  poured  into  a  solution  of 
tannin  gives  a  voluminous  flocculent  precipitate  which  shrinks  and 
and  coagulates  to  a  small  horny-like  mass  when  heated. 

The  quantitative  analysis  of  paper  for  gelatin  is  based  on  the  well- 
known  Kjedahl  method.  The  weighed  portion  of  paper  is  cut  into 
small  pieces  (i  or  2  grm.).  The  amount  of  nitrogen  multiplied  by 
5.56  gives  the  weight  of  gelatin  (absolute  dry)  in  the  quantity  of  paper 
taken  for  analysis.  Pure  dry  gelatin  contains  18.00%  nitrogen. 

Starch  is  readily  detected  by  the  blue  produced  when  the  sample 
is  treated  with  a  weak  solution  of  iodine.  Quantitative  estimation 
are  based  on: 

1.  Extraction  with  suitable  solvents.     A  weighed  quantity  of  paper 
dried  at  100°  is  heated  with  absolute  alcohol  containing  a  few  drops  of 
hydrochloric  acid  to  remove  resinous  substances,  the  amount  of  which 
is  determined  by  loss  of  weight.     The  further  loss  sustained  by  boiling 
with  a  mixture  of  water  and  rectified  spirits  containing  a  few  drops  of 
acid  is  attributed  to  the  removal  of  starch. 

2.  Conversion  of  starch  into  dextrose  by  treating  a  known  weight  of 
paper  with  a  weak  solution  of  sulphuric  acid  and  estimation  of  the 
dextrose  by  means  of  Fehling's  solution. 

Rosin. — The  paper  cut  up  into  small  strips  is  heated  in  a  test-tube 
with  absolute  alcohol  containing  a  few  drops  of  acetic  acid.  The 
extract  when  poured  into  water  gives  a  turbid  solution  more  or  less 
intense  according  to  the  percentage  of  rosin  present  in  the  paper. 

A  little  ether  poured  on  the  surface  of  the  paper  will  dissolve 
the  rosin  present,  which,  as  the  ether  evaporates,  forms  a  brownish 
ring. 

A  strip  of  paper  sized  with  rosin  if  partially  immersed  in  concen- 
trated sulphuric  acid  develops  a  reddish  tint  at  the  edge  in  contact 
with  the  surface  of  the  acid.  There  must  be  no  mechanical  wood  pulp 
present  in  paper  submitted  to  this  test. 


478  PAPER   AND    PAPER- MAKING    MATERIALS. 

The  amount  of  rosin  size  in  paper  is  estimated  by  the  loss  in  weight 
caused  by  extraction  with  absolute  alcohol  containing  a  few  drops  of 
acetic  acid. 

The  proportion  of  rosin  may  also  be  determined  approximately 
by  comparing  the  turbidity  of  the  extract  when  poured  into  water  with 
that  produced  by  adding  a  known  volume  of  a  i%  solution  of  rosin  in 
absolute  alcohol  to  an  equal  volume  of  distilled  water. 

Casein. — Paper  having  a  strong  alkaline  reaction  when  tested  with 
litmus  probably  contains  casein  as  the  sizing  agent.  This  is  chiefly 
used  with  the  so-called  "art  papers."  The  casein  in  paper  is  extracted 
by  boiling  with  sodium  carbonate  or  ammonium  hydroxide.  The 
extract  is  neutralised  with  acetic  acid,  evaporated  to  a  small 
bulk  and  treated  with  a  mixture  of  i  part  strong  sulphuric  acid 
and  2  parts  of  acetic  acid.  A  reddish-violet  is  obtained  which 
indicates  casein.  Gelatin  does  not  give  such  a  pronounced  colour. 
The  proportion  of  casein  present  is  determined  by  the  Kjedahl 
process. 

Impurities  in  paper  consist  of  fibrous  and  other  ingredients  which 
affect  the  physical  properties,  and  soluble  constituents  which  affect  its 
colour  and  durability. 

Fibres. — Occasionally  papers  are  contaminated  with  extraneous 
fibres  which  impair  its  strength.  Common  newspapers  frequently 
break  on  the  printing  machine  owing  to  the  presence  of  undigested 
fibres  of  coarse  wood  pulp  or  jute.  The  latter  is  frequently  derived 
from  string  or  canvas  used  in  packing  wood  pulp.  The  nature  of  such 
fibres  is  determined  microscopically. 

Particles  of  dirt  will  be  found  in  paper  and  may  be  traced,  chiefly 
by  microscopic  examination,  to  coal,  coke,  coarse  imperfectly  ground 
loading,  traces  of  stone  from  the  grindstones  used  for  the  manufacture 
of  mechanical  pulp,  specks  of  iron  and  other  metals,  minute  pieces  of 
rubber  and  similar  substances. 

Transparent  spots  in  paper  are  usually  traceable  to  rosin  derived 
either  from  the  sulphite  wood  pulp  used  in  the  paper  or  to  imper- 
fectly boiled  rosin  size.  Impurities  of  this  character  can  generally 
be  removed  by  extraction  with  absolute  alcohol  and  ether.  Sometimes 
the  transparent  spots  are  due  to  the  crushing  of  the  fibre  by  the  calender 
rolls  used  in  imparting  a  surface  to  the  paper.  If  a  thick  place  in  the 
sheet  is  due  to  the  aggregation  of  a  number  of  fibres,  the  pressure  of 
the  calenders  will  render  the  spot  transparent. 


PAPER    MATERIALS.  479 

Soluble  Constituents. — In  the  process  of  manufacture  certain 
impurities  may  be  left  in  the  pulp  such  as: 

Acid. — The  presence  of  free  acid  in  paper  cannot  be  determined 
with  ordinary  litmus,  since  alum  used  in  sizing  gives  an  acid  reaction 
with  litmus  paper.  The  aqueous  extract  should  be  tested  with  methyl 
orange  and  Congo  red. 

Sulphides,  usually  traceable  to  chemical  wood  pulp,  may  be  detected 
by  boiling  the  paper  in  a  dilute  solution  of  acid  and  allowing  the  steam 
to  impinge  on  the  surface  of  a  filter-paper  impregnated  with  lead  acetate. 

Iron. — Traces  of  iron  salts  tend  to  lower  the  colour  of  ordinary 
paper  and  are,  of  course,  undesirable  in  photographic  papers.  The 
usual  tests  for  iron  can  be  applied. 

Examination  of  Special  Papers. — The  analysis  of  papers  manu- 
factured for  special  purposes  is  governed  largely  by  a  knowledge 
of  the  methods  of  manufacture  or  a  knowledge  of  the  uses  to  which 
the  paper  is  put.  Of  this  we  quote  a  few  examples. 

Tinfoil. — The  amount  of  tin  on  the  surface  of  the  paper  is  ascer- 
tained by  removal  of  the  tin  with  acid  and  subsequent  examination  of 
the  solution. 

Gilt  and  bronze  papers  are  frequently  examined  for  the  nature  of 
the  material  used  in  gilding.  The  substance  is  dissolved  in  acid  and  the 
solution  examined  in  the  ordinary  way.  Most  of  the  matter  used  for 
gilding  consists  of  copper  and  its  alloys. 

Vulcanised  Fibre. — This  is  examined  microscopically  in  order  to 
determine  the  extent  of  the  treatment  with  zinc  chloride  and  any 
traces  of  zinc  can  be  found  by  examination  qf  the  ash  of  the  paper. 

Coated  Papers. — The  heavy  coating  on  so-called  art  and  other  sur- 
faced papers,  being  a  mixture  of  some  inert  mineral  substance,  such  as 
china  clay  or  barytes,  mixed  with  an  adhesive,  such  as  glue  or  casein, 
can  be  removed  by  cautious  treatment  in  hot  water  or  in  a  weak  solu- 
tion of  sodium  carbonate.  A  sheet  of  paper  of  known  area  is  weighed, 
soaked  in  hot  water  or  alkali  and  the  coating  removed  by  cautious 
rubbing  with  a  camel's-hair  brush.  The  "body"  paper,  so-called,  is 
then  dried,  and  the  loss  in  weight  is  a  measure  of  the  amount  of  coating 
substance  used.  The  percentage  of  gelatin  or  casein  can  be  estimated 
in  the  original  coated  paper  by  the  Kjedahl  process. 

Waxed  papers  can  be  treated  with  suitable  solvents  to  remove  the 
wax  with  which  the  paper  is  impregnated. 

Waterproof  Papers. — Extraction  with  alcohol  and  ether  will  re- 


47$  PAPER   AND    PAPER-MAKING    MATERIALS. 

The  amount  of  rosin  size  in  paper  is  estimated  by  the  loss  in  weight 
caused  by  extraction  with  absolute  alcohol  containing  a  few  drops  of 
acetic  acid. 

The  proportion  of  rosin  may  also  be  determined  approximately 
by  comparing  the  turbidity  of  the  extract  when  poured  into  water  with 
that  produced  by  adding  a  known  volume  of  a  i%  solution  of  rosin  in 
absolute  alcohol  to  an  equal  volume  of  distilled  water. 

Casein. — Paper  having  a  strong  alkaline  reaction  when  tested  with 
litmus  probably  contains  casein  as  the  sizing  agent.  This  is  chiefly 
used  with  the  so-called  "art  papers."  The  casein  in  paper  is  extracted 
by  boiling  with  sodium  carbonate  or  ammonium  hydroxide.  The 
extract  is  neutralised  with  acetic  acid,  evaporated  to  a  small 
bulk  and  treated  with  a  mixture  of  i  part  strong  sulphuric  acid 
and  2  parts  of  acetic  acid.  A  reddish-violet  is  obtained  which 
indicates  casein.  Gelatin  does  not  give  such  a  pronounced  colour. 
The  proportion  of  casein  present  is  determined  by  the  Kjedahl 
process. 

Impurities  in  paper  consist  of  fibrous  and  other  ingredients  which 
affect  the  physical  properties,  and  soluble  constituents  which  affect  its 
colour  and  durability. 

Fibres. — Occasionally  papers  are  contaminated  with  extraneous 
fibres  which  impair  its  strength.  Common  newspapers  frequently 
break  on  the  printing  machine  owing  to  the  presence  of  undigested 
fibres  of  coarse  wood  pulp  or  jute.  The  latter  is  frequently  derived 
from  string  or  canvas  used  in  packing  wood  pulp.  The  nature  of  such 
fibres  is  determined  microscopically. 

Particles  of  dirt  will  be  found  in  paper  and  may  be  traced,  chiefly 
by  microscopic  examination,  to  coal,  coke,  coarse  imperfectly  ground 
loading,  traces  of  stone  from  the  grindstones  used  for  the  manufacture 
of  mechanical  pulp,  specks  of  iron  and  other  metals,  minute  pieces  of 
rubber  and  similar  substances. 

Transparent  spots  in  paper  are  usually  traceable  to  rosin  derived 
either  from  the  sulphite  wood  pulp  used  in  the  paper  or  to  imper- 
fectly boiled  rosin  size.  Impurities  of  this  character  can  generally 
be  removed  by  extraction  with  absolute  alcohol  and  ether.  Sometimes 
the  transparent  spots  are  due  to  the  crushing  of  the  fibre  by  the  calender 
rolls  used  in  imparting  a  surface  to  the  paper.  If  a  thick  place  in  the 
sheet  is  due  to  the  aggregation  of  a  number  of  fibres,  the  pressure  of 
the  calenders  will  render  the  spot  transparent. 


PAPER    MATERIALS.  479 

Soluble  Constituents. — In  the  process  of  manufacture  certain 
impurities  may  be  left  in  the  pulp  such  as: 

Acid. — The  presence  of  free  acid  in  paper  cannot  be  determined 
with  ordinary  litmus,  since  alum  used  in  sizing  gives  an  acid  reaction 
with  litmus  paper.  The  aqueous  extract  should  be  tested  with  methyl 
orange  and  Congo  red. 

Sulphides,  usually  traceable  to  chemical  wood  pulp,  may  be  detected 
by  boiling  the  paper  in  a  dilute  solution  of  acid  and  allowing  the  steam 
to  impinge  on  the  surface  of  a  filter-paper  impregnated  with  lead  acetate. 

Iron. — Traces  of  iron  salts  tend  to  lower  the  colour  of  ordinary 
paper  and  are,  of  course,  undesirable  in  photographic  papers.  The 
usual  tests  for  iron  can  be  applied. 

Examination  of  Special  Papers. — The  analysis  of  papers  manu- 
factured for  special  purposes  is  governed  largely  by  a  knowledge 
of  the  methods  of  manufacture  or  a  knowledge  of  the  uses  to  which 
the  paper  is  put.  Of  this  we  quote  a  few  examples. 

Tinfoil. — The  amount  of  tin  on  the  surface  of  the  paper  is  ascer- 
tained by  removal  of  the  tin  with  acid  and  subsequent  examination  of 
the  solution. 

Gilt  and  bronze  papers  are  frequently  examined  for  the  nature  of 
the  material  used  in  gilding.  The  substance  is  dissolved  in  acid  and  the 
solution  examined  in  the  ordinary  way.  Most  of  the  matter  used  for 
gilding  consists  of  copper  and  its  alloys. 

Vulcanised  Fibre. — This  is  examined  microscopically  in  order  to 
determine  the  extent  of  the  treatment  with  zinc  chloride  and  any 
traces  of  zinc  can  be  found  by  examination  qf  the  ash  of  the  paper. 

Coated  Papers. — The  heavy  coating  on  so-called  art  and  other  sur- 
faced papers,  being  a  mixture  of  some  inert  mineral  substance,  such  as 
china  clay  or  barytes,  mixed  with  an  adhesive,  such  as  glue  or  casein, 
can  be  removed  by  cautious  treatment  in  hot  water  or  in  a  weak  solu- 
tion of  sodium  carbonate.  A  sheet  of  paper  of  known  area  is  weighed, 
soaked  in  hot  water  or  alkali  and  the  coating  removed  by  cautious 
rubbing  with  a  camel's-hair  brush.  The  "body"  paper,  so-called,  is 
then  dried,  and  the  loss  in  weight  is  a  measure  of  the  amount  of  coating 
substance  used.  The  percentage  of  gelatin  or  casein  can  be  estimated 
in  the  original  coated  paper  by  the  Kjedahl  process. 

Waxed  papers  can  be  treated  with  suitable  solvents  to  remove  the 
wax  with  which  the  paper  is  impregnated. 

Waterproof  Papers. — Extraction  with  alcohol  and  ether  will  re- 


480  PAPER   AND    PAPER-MAKING    MATERIALS. 

move  lac,  rosin  and  similar  products  employed  for  the  purpose  of 
making  paper  waterproof.  Borax,  alum,  glue  and  metallic  oxides  may 
be  sought  for  in  papers  of  this  class. 

Cheque  Papers. — Iron  ferrocyanides  mixed  with  other  ferrocyanides, 
together  with  potassium  and  sodium  iodides,  are  frequently  used  in 
papers  of  this  class  and  may  be  found  in  the  aqueous  extract  of  the 
paper  or  by  applying  suitable  reagents  to  the  surface  of  the  paper. 
Other  salts  may  be  found  by  careful  examination  of  the  aqueous  extract. 

WOOD  PULP. 

Mechanical  Wood  Pulp. — The  quality  of  this  material  .is  deter- 
mined chiefly  by  its  freedom  from  coarse  heavy  chips  known  as  shives. 
These  are  slivers  of  pulp  produced  during  the  grinding  of  the  wood 
which  have  not  been  properly  removed  by  the  strainers.  The  propor- 
tion present  in  a  sample  of  pulp  may  be  found  by  macerating  the  latter 
in  a  mortar,  agitating  the  mass  in  a  large  quantity  of  water,  and 
separating  the  shives  by  a  process  of  elutriation.  Mechanical  pulp 
should  not  be  contaminated  with  jute  fibres  from  the  canvas  used  in 
manufacture  nor  with  particles  of  stone  from  the  grindstones. 
The  presence  of  mechanical  pulp  in  paper  is  readily  detected  by  the 
intense  yellow  produced  when  a  sheet  of  the  paper  is  moistened  with 
a  4%  solution  of  aniline  sulphate. 

Another  useful  reagent  is  phloroglucinol,  which  imparts  a  reddish 
tint  to  paper  containing  mechanical  pulp,  the  depth  being  proportional 
to  the  amount  present  The.  reagent  is  prepared  by  dissolving  2 
grm.  of  phloroglucinol  in  50  c.c.  absolute  alcohol  and  adding  25 
c.c.  of  hydrochloric  acid.  It  should  be  noted  that  papers  coloured 
with  metanil  yellow  are  instantly  turned  to  a  reddish  shade  by  the 
acid  in  the  reagent,  and  this  effect  must  not  be  confused  with  the 
mechanical  pulp  reaction. 

The  proportion  of  mechanical  wood  in  a  paper  is  judged  by  this 
colour  test  or  by  a  microscopical  examination.  A  method  has  recently 
been  introduced  for  estimating  the  amount  by  a  volumetric  process. 
It  depends  on  the  absorption  of  the  phloroglucinol  by  the  ligno- 
cellulose  of  the  pulp  and  a  titration  of  the  unabsorbed  reagent  by 
formaldehyde. 

Chemical  Pulp.— Wood  cellulose  is  isolated  by  3  processes: 
treatment  with  calcium  hydrogen  sulphite  (bisulphite)  or  with  sodium 


FIG.  77. — Straw  pulp;  small  cells  from  washings 


FIG.  78. — Manila  hemp. 


(To  face  page  480.) 


FIG    79. — Mechanical  wood  pulp  (ground  wood). 


FIG.  80. — Esparto  pulp. 


FIG  81. — Poplar  pulp. 


FIG.  82.— Cotton  pulp. 


FiG.  83. — Linen  pulp. 


FIG.  84. — Bamboo  pulp. 


FIG.  85  — Spruce  pulp. 


(To  face  page  480.) 


WOOD    PULP.  481 

hydroxide  or  with  a  mixture  of  sodium  hydroxide  and  sodium  sulphide. 
These  pulps  are  usually  described  as  sulphite,  soda  and  sulphate  pulps. 
The  last  two  are  for  all  practical  purposes  the  same  and  are  readily 
distinguished  in  their  commercial  forms  from  the  sulphite  by  the  dif- 
ference in  feel,  bulk  and  texture.  The  chemical  differences  are  very 
slight,  the  sulphite  pulp  containing  0.5%  resin  in  contrast  with  soda 
pulps  which  contain  0.05%.  Slight  differences  also  in  behaviour  towards 
certain  aniline  dyes,  such  as  malachite  green  and  saffranin,  are  used 
for  distinguishing  the  fibres  when  examined  microscopically,  but  the 
reactions  are  not  of  a  very  definite  character.  It  is  therefore  difficult 
to  determine  the  proportions  present  in  a  paper  which  contains  both 
classes  of  pulp  and  at  present  no  exact  methods  are  known  by  which 
the  complete  absence  of  a  soda  pulp  in  a  paper  presumed  to  be  all 
sulphite,  or  vice  versa,  can  be  ascertained. 

Moisture  in  Wood  pulp. — The  pulp  used  for  paper-making  is  sup- 
plied in  the  condition  of  dry  sheets  or  of  moist  sheets  containing  50% 
of  air-dry  pulp.  The  air-dry  pulp  is  calculated  on  the  basis  of  10% 
moisture;  that  is,  90  parts  of  absolute  dry  pulp  (dried  at  100°)  is* 
equivalent  to  100  parts  of  air-dry  pulp.  All  supplies  are  tested  for 
moisture. 

According  to  regulations  agreed  to  by  pulp  manufacturers  and 
paper-makers,  not  less  than  2%  and  not  more  than  4%  of  the  number 
of  bales  in  a  consignment  are  selected,  such  bales  being  sound,  intact 
and  representative.  From  each  bale,  when  weighed,  3  or  5  sheets  are 
drawn  and  sampled  by  what  is  known  as  the  "  wedge"  system.  A  wedge 
having  its  apex  at  the  centre  of  the  sheet  and  its  base  at  the  outer  edge 
mathematically  constitutes  a  fair  sample  of  the  sheet.  The  wedges 
are  cut  with  bases  of  varying  width  if  necessary  in  order  to  obtain 
samples  that  correspond  with  the  volume  of  pulp  they  are  supposed 
to  represent. 

The  sample  of  pulp  is  weighed,  dried  at  100°  in  a  water-oven,  and 
the  absolute  dry  weight  determined. 

The  usual  form  of  British  certificate  is  as  follows: 


VOL.  1—31 


482 


PAPER   AND    PAPER-MAKING    MATERIALS. 


JO, 
(X, 

«*i 

a  & 
rt  a 


o 


M 
U 

PH 

r^oo        10  O 

<N  i>    <? |>: 

T*.    W-»  IO    O 


" 


3  3 
o- 


3|Sg 

S|S| 
P    B  -732 

2  I  s  , 


^^ 


- 
1 

" 


5"    fS    O 


£         en  2 

O      r/T    Q.  ^    S  .,   (      3J 

.23  "3  «»       ^  ^  "I  -   - 

"-"  jD    01  X3    c 

•"2         Kn  QJ 


o 
M  H      H 


e   -2 

8  S      •- 


CJ  -t_> 

S          a. 
3 

PH 


f 


\O  vO    -«t  M    O\O    00 


WOOD    PULP.  483 

The  following  is  the  usual  form  of  the  American  certificate: 

Moisture  @  100°  C., 

Bone-dry  pulp, 

Air-dry  pulp,  on  10%  basis 

of  the  above  bales,  carefully  selected,  (weighing  Ibs.)  were  opened, 
and  an  outside,  an  intermediate,  and  an  inner  sheet  were  taken  from  each: 
portions  of  all  these  sheets  were  kept  in  an  air-tight  vessel  for  the  above  analysis 

The  Bleaching  of  Wood  Pulp. — The  amount  of  bleaching  powder 
required  to  bleach  sulphite,  soda  and  sulphate  wood  and  other  half 
stuffs  is  an  important  factor.  The  percentage  consumption  varies 
with  different  pulps. 

Esparto,  10-15%. 

Soda  wood,       18-25%. 
Sulphite  wood,    9-20%. 

From  the  carefully  selected  representative  sample,  a  small  quantity 
of  5  or  10  grm.  is  accurately  weighed  out  and  macerated  with 
a  little  warm  water  in  a  mortar  so  as  to  thoroughly  break  up  the  pulp 
into  a  fibrous  condition.  The  moist  pulp  is  transferred  to  a  convenient 
sized  beaker  or  jar  and  a  clear  solution  of  chloride  of  lime  added,  the 
quantity  being  determined  by  the  nature  of  the  fibre.  It  is  best  to 
add  liquor  containing  available  chlorine  equivalent  to  25%  of  bleaching 
powder  calculated  on  the  air-dry  weight  of  pulp.  The  mixture  is  kept 
for  2  or  3  hours  at  a  temperature  of  38°  C.  to  40°  C.,  being  frequently 
stirred  until  the  colour  is  white.  If  insufficient  bleach  liquor  has  been 
added,  the  chlorine  may  be  exhausted  before  the  pulp  is  white,  as 
indicated  by  a  starch-iodide  test-paper.  When  the  colour  is  sat- 
isfactory, the  liquor  is  filtered  off  and  titrated  with  decinormal  arsenic 
solution  in  order  to  determine  the  amount  of  bleach  unconsumed.  If 
a  considerable  excess  of  bleach  has  been  used  in  the  first  experiment, 
the  test  should  be  repeated,  using  only  a  slight  excess  of  clear  bleach 
liquor  over  and  above  the  amount  shown  to  be  consumed  in  the  first. 

Example: 

Decinormal  arsenic  solution,  i  c.c.  =  0.00355  g™1-  chlorine 

=  0.0 1  grm.  normal  bleaching  powder. 

Bleach  liquor  used,  i  c.c.  =3.8  c.c.  arsenic 

=  0.038  grms.  normal  bleaching  powder 

Pulp  taken,  10  grms. 

Bleaching  powder  added,  2  grms. 

in  the  form  of  solution,  52.62  c.c. 

Arsenic  required  to  neutralise  unconsumed  bleach,  7.6  c.c. 


484  PAPER   AND    PAPER- MAKING    MATERIALS. 

Bleaching  solution  actually  used,  50.62  c.c. 

=  i  .923  grms.  powder 
Bleaching  powder  consumed  by  air-dry  pulp  =  19.2%. 

Examination  of  New  Fibres  for  Paper-making. — The  scheme  of 
analysis  generally  adopted  for  plant  substances  is  that  devised  by  Cross 
and  Bevan,  which  is  shown  in  the  following  schedule: 

Moisture,  Hygroscopic  water,  or  water  of  condition. 

Loss  in  drying  at  100°. 

Fat,  wax  and  resin,     By  extraction  with  solvents. 
Ash,  Residue  left  on  ignition. 

Hydrolysis  (a),  Loss   of   weight  on  boiling  5  minutes  in  i%  solution  of 

sodium  hydroxide. 

(b),  Loss  of  weight  on  continuing  to  boil  one  hour. 

Cellulose,  Boiling  with  weak  alkali,  exposure  of  washed  product  to 

chlorine  gas,  and  heating  in  solution  of  sodium  sulphite. 

Final  immersion  in  sodium  hyposulphite. 

Mercerising,  Loss  of  weight  on  treating  i  hour  with  15  to  25%  solu- 

tion sodium  hydroxide. 
Nitration,  Weight  of  nitrated  product  obtained  by  treatment  with 

mixture  of  equal  volumes  of  nitric  and  sulphuric  acids  one 

hour  in  cold. 
Acid  purification,        Loss  of  weight   after  boiling  with   20%  acetic  acid  and 

and  washing  with  water  and  alcohol. 
Carbon  percentage,     Combustion  with  chromic  acid  after  solution  in  sulphuric 

acid. 

Yield  of  Paper-making  Fibre. — The  suitability  of  a  new  material  is 
best  determined  by  treatment  of  500  to  1000  grm.  The  fibre  previ- 
ously cut  up  into  small  pieces  is  packed  closely  in  an  autoclave, 
covered  with  sodium  hydroxide  solution  of  known  density,  strength, 
and  boiled  for  6  or  7  hours  at  a  definite  pressure.  For  a  first  trial  the 
alkali  solution  should  have  a  sp.  gr.  of  1.050  and  the  pressure  should  not 
exceed  60  pounds  per  square  in.  These  conditions  will  be  modified  in 
the  succeeding  trials  according  to  the  results  of  the'first.  The  resultant 
pulp  is  washed  and  immersed  in  a  known  volume  of  bleach  liquor  for 
2  or  3  hours  at  38°.  The  bleached  pulp  is  removed,  and  any  avail- 
able chlorine  still  remaining  in  the  residual  liquor  estimated  by  means 
of  standard  arsenical  solution. 

The  pulp  is  washed  thoroughly  and  made  up  into  small  sheets  for 
convenience.  The  fibre  of  the  pulp  is  examined  microscopically  and 
a  record  made  of  the  dimensions  and  general  characteristics. 

The  total  yield  of  paper-making  fibre  from  the  plant  substance  is, 
of  course,  easily  obtained  by  this  experiment.  The  sodium  hydroxide 
used  is  ascertained  by  titration  of  the  residual  liquor  from  the  digester. 
In  actual  practice,  the  solution  must  be  sufficient  in  quantity  to  cover 
the  fibre  and  of  sufficient  strength  to  effect  the  isolation  of  the 
cellulose.  Hence  a  considerable  excess  is  always  necessary. 


ACID  DERIVATIVES  OF  ALCOHOLS.1 


(VEGETABLE  ACIDS). 

BY  HENRY  LEFFMANN. 

These  acids  are  numerous  and  form  well-marked  series  of  salts. 
In  concentrated  form  they  are  mostly  actively  corrosive,  and  even  when 
considerably  diluted  with  water  produce  strongly  acid  liquids  which 
affect  nearly  all  indicators  and  dissolve  oxides  and  carbonates;  a  few 
of  them  dissolve  such  metals  as  iron  and  zinc.  Many  of  them  are  vola- 
tile at  ordinary  temperatures;  others,  that  are  not  so  readily  volatile, 
distil  with  open  steam;  some  distil  only  with  superheated  steam. 
The  salts  are  mostly  colourless  unless  formed  with  colour-producing 
metals,  and  are  usually  without  odour,  but  the  liability  of  many  of  them 
to  hydrolyse  slightly  often  causes  the  apparently  pure  salt  to  have 
the  odour  of  the  acid  from  which  it  was  produced.  All  the  salts  are 
decomposed  by  heating,  generally  leaving  a  residue  of  carbonate  with 
free  carbon,  but  when  an  easily  reducible  metal  is  present,  the  residue 
may  be  either  an  oxid  or  the  free  element. 

The  following  table  shows  the  manner  in  which  the  neutral  solu- 
tions of  the  potassium  or  sodium  salts  of  the  acids  of  this  division  are 
affected  by  cold  neutral  solutions  of  barium,  calcium  and  ferric 
chlorides,  lead  acetate  and  silver  nitrate.  The  reactions  refer  to  mod- 
erately concentrated  solutions  of  the  salts.  When  the  precipitate  is 
somewhat  soluble  in  water,  so  as  to  render  its  production  uncertain,  the 
letter  P  is  placed  within  parentheses.  S  signifies  that  the  substance 
formed  is  soluble,  and  hence  that  no  precipitate  is  obtained.  Except 
when  otherwise  mentioned,  the  precipitates  are  white.  In  addition  to 
the  reactions  with  the  above  metallic  solutions,  columns  are  added 
showing  the  reactions  of  the  organic  acids  with  other  important 
reagents.  R  signifies  " reduction"  and  o  "no  effect": 

1 1  am  under  obligations  to  Mr.  W.  A.  Davis  for  numerous  emendations  and  corrections 
of  this  article,  especially  in  relation  to  tartaric  and  citric  acids. — H.  L. 

485 


486 


ACID    DERIVATIVES    OF    ALCOHOLS. 


TABLE  SHOWING  THE  REACTIONS  OF   THE    SALTS  OF  SOME  OF 
THE  VEGETABLE  ACIDS. 


•8 

5 

13 

w 

B 

•c                      & 

"bo 

£  « 

J3 

o 

ci 

(3 

1.8 

Name  of 
salt  in 
solution 

0 

.3 

I 
•S 

th  calcium  ch 

With  ferric 
chloride 

13 
1 

With 
silver 
nitrate 

1| 
11 

•§ 

;h  permangar 
old  acid  solut 

With  hot 
concen- 
trated   sul- 
phuric acid 

Remarks 

£ 

^ 

g 

Acetate,         S 

S 

Red 

S 

(P) 

O 

Odour  of 

Silver  salt  not 

acetic 

reduced     on 

acid. 

heating  solu- 

tion. 

Formate, 

s 

S 

Red 

s 

(S) 

R 

Carbon 

Silver    salt    or 

monoxide 

solution    re- 

evolved. 

d  u  c  e  d   on 

heating. 

Oxalate, 

p 

P 

S 

p 

P 

0 

R 

Carbon 

A  yellow    pre- 

monoxide 
and  dioxide 

cipitate  some- 
times    occurs 

evolved.    !     on  adding  fer- 
ric chloride. 

Lactate, 

s 

S 

S 

s 

S 

0 

R 

Carbon 

See  Lactic  acid. 

monoxide 

evolved  . 

Brown 

colour. 

Succinate, 

(P) 

(S) 

Red-brown 
precipitate. 

p 

P 

o 

o 

No  change 

Barium     and 
calcium  salts 

precipitat  e  d 

on  adding  al- 

cohol. 

Malate, 

s 

(S) 

S 

p 

P 

o 

R 

Darkened.  I   Calcium     salts 

in  soluble    in 

dilute    al- 

cohol. 

Tartrate, 

p 

p 

S 

p 

P 

0 

R 

Charring. 

Silver   salt   re- 

duced     on 

heating. 

Citrate, 

p 

p 

S 

p 

P 

o 

o 

Carbon 

Calcium     salt 

monoxide 

precipitat  e  d 

evolved. 

on  boiling 

x 

and    redis- 

Brown. 

solved    on 

cooling. 

Aconitate,    (P) 

(P) 

p 

P 

Calcium  salt  is 

soluble  in 

100  parts  of 

water. 

Meconate,    (P) 

p 

Red 

p 

P 

Action   of  oxi- 

dising  agents 

not  recorded. 

Colour  Reactions  for  Organic  Acids. — Some  phenolic  derivatives 
give  colours  with  these  acids.  Messrs.  H.  J.  H.  Fenton  and  G.  Barr 
have  made  a  number  of  comparative  experiments.  They  find  that  not 
only  the  acids,  but  their  salts  and  esters  can  be  detected  even  in  minute 
amount  by  the  reagents  they  used.  The  substance  to  be  tested  is 
mixed  with  strong  sulphuric  acid  and  the  reagent.  In  testing  dry 
material  it  is  necessary  to  add  a  drop  of  water  before  deciding  upon 


VEGETABLE   ACIDS. 


487 


the  result.  The  following  is  an  abstract  of  the  method  (Proc.  Cam- 
bridge Philosoph.  Soc.,  1907,  14,  386).  In  the  table,  A  indicates 
the  result  on  adding  ammonium  hydroxide  after  the  reagents  have 
been  allowed  to  act  for  a  short  time.  The  changes  are  sometimes 
slow.  Many  acids  were  tried.  The  following,  among  others,  gave 
no  characteristic  results:  Tartaric,  citric,  suberic,  sebacic,  mucic, 
malic,  succinic,  malonic,  hippuric,  acetic,  butyric,  stearic,  amino- 
acetic,  cinnamic. 


Acid 


Resorcinol 


Phenol 


Pyrogallol 


1-2  Cresol 


Formic      Strong  orang  e-red    Pink, 
changing  to  blood- 
red.      A,   to   dilute 
solution,   green  be- 
coming purple. 


Pink,  passing  to  or-     Light  red. 
ange-red  and  | 
scarlet. 


Oxalic      Slight  yellow,  passing   Faint   pinkj  Dirty  green  passing  j  Crimson.  A, 


to  dark  blue.  A, 
change  to  pink. 

passing  to 
red. 

to  orange.  A, 
changes  to  intense 
blue,  then  pur- 
plish-brown. 

gives  pur- 
ple. 

Lactic  Yellow  passing  to  or- 
ange. A,  gives  flu- 
orescent green. 

Yellow  o  r 
orange. 

Orange. 

Red-brown. 

The  following  special  methods  with  resorcinol  are  given  by  Mulliken 
(Identij.  Pure  Org.  Comps.,  Vol.  I): 

A  small  amount  of  the  acid  is  mixed  with  a  few  drops  of  a  freshly- 
prepared  solution  of  resorcinol,  the  dish  placed  on  the  water-bath  and 
at  intervals  of  half  a  minute  portions  of  the  liquid  are  removed  and  the 
depth  of  colour  noted.  When  the  maximum  is  reached,  the  liquid 
is  diluted  cautiously  with  water  and  the  colour  changes  noted. 

Citric  acid,  pale  greenish-blue,  changing  blue-green,  then  to  pale 
impure  green.  Colour  after  dilution  much  paler. 

Tartaric  acid,  pale  blue-green  for  a  moment,  then  pure  intense 
green.  Dilution  with  water  gives  orange-yellow. 

Malic  acid,  momentary  greenish-yellow  changing  to  intense  yellow, 
which  is  permanent.  Dilution  gives  orange-yellow  more  intense  than 
from  the  other  two  acids. 


488  ACID    DERIVATIVES    OF   ALCOHOLS. 

Acetic  Acid. 

This  occurs  in  some  plants  and  is  a  frequent  product  in  chemical 
reactions.  It  is  produced  by  the  acetic  fermentation  of  sugar  and 
by  the  limited  oxidation  of  alcohol.  A  large  quantity  is  obtained  by 
the  distillation  of  wood.  The  crude  material  from  this  source  is 
usually  termed  "  pyroligneous  acid.  " 

Acetic  acid  is  a  colourless  liquid,  strongly  acid  and  pungent.  It  crys- 
tallises in  transparent  plates,  melting  at  16.7°,  and  hence  is  often 
termed  " glacial  acetic  acid."  Acetic  acid  remains  liquid  if  cooled 
in  a  closed  vessel,  even  below  o°,  but  on  opening  or  shaking  the  vessel 
or  dropping  in  a  fragment  of  the  solid  acid,  the  whole  solidifies  and 
the  temperature  rises  to  16.7°.  A  small  addition  of  water  lowers 
the  m.p.  of  acetic  acid  very  considerably,  so  that  an  acid  contain- 
ing 13%  of  water  melts  below  o°,  and  one  containing  38%  of  water 
(corresponding  to  C2H4O2  +  2H2O)  has  a  m.p.  of  —24°.  More  water 
raises  the  m.  p. 

Acetic  acid  boils  at  119°  and  distills  unchanged.  In  distilling  hy- 
drated  acid  the  last  fractions  are  absolute  or  nearly  so. 

Addition  of  water  to  acetic  acid  causes  evolution  of  heat,  and  con- 
traction in  volume  until  the  mixture  contains  about  23%  of  water, 
Acid  of  this  strength  has  a  higher  sp.  gr.  than  the  glacial  acid,  so  that 
either  concentration  or  dilution  causes  a  diminution.  The  sp.  gr. 
of  moderately  concentrated  solutions  of  acetic  cannot  be  used  in  as- 
certaining their  strength,  but  is  of  service  in  examining  the  dilute 
solutions. 

The  table  on  page  489  taken  from  the  United  States  Pharmaco- 
poeia, 1900-05  (8th  decennial  revision)  shows  the  sp.  gr.  of  acetic  acid 
of  different  strengths,  all  figures  being  at  i5°/i5°.  It  will  be  seen 
by  the  table  that  acid  of  100%  and  acid  of  approximately  43%  will 
coincide  in  gravity. 

Absolute  acetic  acid  is  miscible  in  all  proportions  with  water,  alcohol 
and  ether.  It  is  powerfully  corrosive,  dissolves  many  essential  oils, 
camphor  and  resins,  phenols,  gelatin  and  many  metallic  salts  insolu- 
ble in  water.  The  liquid  acid  is  not  inflammable,  but  the  vapour 
burns  with  a  blue  flame. 

Acetic  acid  is  stable.  The  most  powerful  oxidising  agents  attack  it 
with  difficulty.  Chromic  acid  has  no  effect  on  it;  a  solution  of  chromic 
acid  in  acetic  acid  is  employed  for  the  oxidation  of  hydrocarbons. 
Nitric  acid  has  no  action;  chlorine  converts  it  into  chloracetic  acid. 


ACETIC   ACID. 

489 

Per  cent. 

Sp  gr.            Per  cent. 

II 

Sp.  gr. 

Per  cent.           Sp.  gr. 

1                      I 

i                  1.0015                   19 

.0278 

37 

[.0500 

2 

.  0030                           20 

.0292 

38 

[  .0510 

3 

.O045                           21 

.0306 

39                1-0521 

4 

.OO6o                           22               1      i 

.0319 

40 

1.0531 

5 

-0075 

23 

•0332 

45 

r-0579 

6 

.0090 

24 

•°345 

50 

.0623 

7 

.0105 

25 

-0358 

55 

.0661 

8 

.0120 

26 

.0371 

60 

[.0693 

9 

•0135 

27 

.0384 

65 

.0720 

10 

.0150 

28 

.0396 

7o 

.0741 

ii 

.0165 

29 

.0408 

75 

•0754 

12 

.0179 

30 

.0420 

80 

.0756 

13 

.0193 

31 

.0432 

85                1.0747 

14 

.02O8                         32 

.0444 

90                1.0721 

15 

.0222                         33 

•0455 

95                1.0668 

16 

.0236 

34 

.0467 

100                  1.0562 

I7 

.0250 

35 

.0478 

i 

18                   .0264                  36 

.0489 

Detection  of  Acetic  Acid  and  Acetates. — Most  of  the  acetates 
are  soluble  in  water.  A  few  oxyacetates  (" basic"  acetates)  are  in- 
soluble; silver  and  mercurous  acetates  are  sparingly  soluble.  Hence, 
acetic  acid  cannot  be  estimated  or  readily  detected  by  precipitation. 
Free  acetic  acid  may  generally  be  recognised  by  its  odour  and  other 
physical  properties,  or  it  may  be  neutralised  by  sodium  hydroxide 
and  examined  by  the  following  tests: 

Metallic  acetates  give  the  following  reactions : 

Subjected  to  dry  distillation,  acetone,  is  given  off,  having  a  highly 
•characteristic  odour. 

Heated  in  the  solid  state  in  admixture  with  arsenous  oxide  (As2O3), 
acetates  give  an  alliaceous  and  very  characteristic  odour  of  kakodylic 
oxide.  Only  a  very  minute  amount  of  materials  should  be  used  in 
this  test,  as  the  products  are  very  poisonous. 

Heated  with  sulphuric  or  phosphoric  acid,  acetic  acid  is  evolved. 

Heated  with  alcohol  and  concentrated  sulphuric  acid,  the  fragant 
and  characteristic  ethyl  acetate  (acetic  ether)  is  produced. 

The  neutral  solution,  on  treatment  with  ferric  nitrate  or  ferric 
chloride,  avoiding  excess,  gives  a  deep  red  liquid  containing  ferric  acetate 
This  is  decomposed  on  boiling,  the  liquid  becoming  colourless  and  de- 
positing reddish-brown  ferric  oxyacetate.  The  reaction  is  imper- 
fect if  the  iron  solution  is  added  in  excess.  The  cold  red  liquid  is  not 


49°  ACID    DERIVATIVES    OF    ALCOHOLS. 

decolourised  on  addition  of  mercuric  chloride  (distinction  between 
acetates  and  thiocyanates) ;  and  is  not  taken  up  by  ether  on  agitation 
(distinction  from  thiocyanates) ;  but  the  colour  is  readily  destroyed  on 
addition  of  cold  dilute  sulphuric  or  hydrochloric  acid  (distinction  from 
meconates). 

Insoluble  (basic)  acetates  may  be  converted  into  sodium  acetate 
by  boiling  with  sodium  carbonate  and  filtering  off  the  insoluble  car- 
bonate. 

Acetates  containing  nitrogenous  bases  respond,  as  a  rule,  to  the  fore- 
going tests,  but  the  acetic  esters  do  not.  The  latter  can,  however,  be 
saponified  by  alcoholic  alkali  (see  page  232),  and  after  distilling  off  the 
alcohol  the  acetate  can  be  examined. 

Assay  of  Acetic  Acid  and  Acetates. — For  samples  consisting 
only  of  acetic  acid  and  water  the  sp.  gr.  will  often  furnish  suffi- 
cient information  or  the  liquid  may  be  titrated. 

Phenolphthalein  is  applicable  as  indicator,  sodium  acetate  being 
neutral  to  it,  but  alkaline  to  litmus.  The  end-reaction  is  sharp. 
Highly-coloured  liquids,  such  as  vinegar,  may  be  largely  diluted  before 
titrating,  as  the  delicacy  of  the  reaction  is  but  little  diminished. 

Methyl-orange  and  phenacetolin  are  not  suitable  indicators  for 
titrating  acetic  acid. 

Acetates  containing  metals  of  the  alkalies  and  alkaline  earths  are 
converted  into  carbonates  on  ignition.  In  many  cases  the  amount  of 
acetate  originally  present  may  be  ascertained  by  titrating  with  standard 
acid,  the  residue  of  the  ignition.  Each  c.c.  of  normal  acid  required 
for  neutralisation  represents  0.060  grm.  of  acetic  acid  in  the  sample. 

Salts  of  metals  completely  precipitated  by  sodium  carbonate  (e.  g., 
calcium,  lead,  iron)  may  be  decomposed  by  a  known  quantity  of  it, 
the  liquid  well  boiled,  filtered,  and  the  filtrate  titrated  w.ith  standard 
acid.  The  loss  of  alkalinity  represents  the  acetic  acid  originally 
present  as  an  acetate.  Before  adding  the  sodium  carbonate  the  solu- 
tion must  be  neutral. 

In  presence  of  salts  of  inorganic  acids,  the  last  method  is  valueless, 
but  a  modification  may  be  employed:  The  excess  of  sodium  carb  nate 
is  neutralised  by  hydrochloric  acid,  the  liquid  evaporated  to  dryness, 
the  residue  gently  ignited,  and  the  resultant  carbonate  titrated  with 
standard  acid.  Each  c.c.  of  standard  acid  used  represents  0.060  grm. 
of  acetic  acid.  Other  organic  acids  that  may  be  present  will  be 
included  as  acetic  acid. 


ACETIC   ACID.  4QI 

Free  acetic  acid  may  also  be  determined  by  adding  excess  of  pure 
precipitated  barium  carbonate  to  the  solution.  The  liquid  is  well 
boiled,  filtered,  and  the  barium  in  the  nitrate  precipitated  by  dilute 
sulphuric  acid.  233  parts  of  precipitate  obtained  represent  120  of 
acetic  acid  in  the  sample  taken.  This  process  is  applicable  in  pres- 
ence of  oxalic,  phosphoric,  sulphuric  and  other  free  acids  forming 
insoluble  barium  salts,  but  is  useless  in  presence  of  soluble  oxalates, 
phosphates  and  sulphates.  The  method  is  available  in  presence  of 
alkaline  chlorides,  but  not  in  presence  of  free  hydrochloric  acid,  un- 
less the  solution  is  previously  treated  with  excess  of  silver  sulphate. 
Acetates  and  chlorides  of  metals  of  the  alkalies  and  the  alkaline 
earths  do  not  interfere,  but  acetates  and  other  salts  of  iron,  aluminum 
and  other  metals  precipitable  by  barium  carbonate  must  be  absent. 

The  estimation  of  acetic  acid  in  acetates  is  best  effected  by  dis- 
tilling the  salt  to  dryness  with  a  moderate  excess  of  sulphuric  acid  or 
with  acid  sodium  sulphate.  Water  should  then  be  added  to  the  con- 
tents of  the  retort  and  the  distillation  repeated.  A  third,  and  even  a 
fourth  distillation  will  sometimes  be  necessary,  as  the  last  traces  of 
acetic  acid  are  volatilised  with  difficulty. 

In  presence  of  chlorides,  excess  of  silver  sulphate  should  be  added 
before  commencing  the  distillation. 

In  presence  of  sugar  or  other  bodies  liable  to  decomposition  by  sul- 
phuric acid,  phosphoric  acid  should  be  substituted  .  Care  should  be 
taken  that  the  phosphoric  acid  used  is  free  from  nitric  and  other  vola- 
tile acids.  This  is  best  insured  by  adding  a  little  ammonia  and  heat- 
ing the  acid  to  fusion  in  a  platinum  crucible. 

For  the  estimation  of  acetic  acid  in  presence  of  its  homologues,  see 
the  analysis  of  calcium  acetate. 

Pyroligneous  Acid. — Pyroligneous  acid  or  wood  vinegar  is  the 
crude  acetic  acid  obtained  by  the  distillation  of  wood.  It  is  a  very 
complex  product,  containing,  among  other  substances,  homologues 
of  acetic  acid  from  formic  to  caproic  acid;  cro tonic  and  angelic  acids; 
furfural;  bodies  of  indefinite  nature  called  "wood-oils";  pyrocatechol; 
acetone  and  other  ketones  of  the  acetic  and  oleic  series;  methyl  alcohol 
and  the  other  constituents  of  wood-spirit.  By  neutralising  the  crude 
product  with  lime  and  distilling,  the  volatile  substances  of  indifferent 
nature  are  removed.  When  partially  concentrated,  the  solution  is 
faintly  acidulated  with  hydrochloric  acid,  when  creasote  and  various 
tarry  matters  separate  out;  and  the  clear  liquid  on  evaporation  to  dry- 


4Q2  ACID    DERIVATIVES    OF   ALCOHOLS. 

ness  yields  a  brownish  residue,  which  is  heated  to  about  230°  to  de 
compose  the  empyreumatic  products.  On  distillation  with  hydro- 
chloric acid  a  comparatively  pure  acid  may  be  obtained,  which  can  be 
further  purified  by  rectification  with  a  little  potassium  dichromate. 
A  better  product  is  said  to  be  obtainable  by  converting  the  acid  into 
a  sodium  salt,  heating  to  destroy  tarry  matters  and  distilling  with 
hydrochloric  or  sulphuric  acid. 

The  empyreumatic  odour  of  acetic  acid  derived  from  the  dry  distil- 
lation of  wood  is  in  great  measure  due  to  furfural,  vapours  of  which  are 
always  produced  if  a  warm  mixture  of  sulphuric  acid  and  water  is 
poured  on  bran  or  sawdust,  or  if  bran  is  distilled  with  an  equal  weight 
of  sulphuric  acid  and  three  parts  of  water.  If  the  vapours  of  furfural 
are  evolved  in  a  beaker  covered  with  filter-paper  soaked  in  aniline,  the 
latter  will  turn  red,  but  this  soon  disappears.  This  reaction  may  be 
employed  for  the  detection  of  furfural  which  may  be  removed  from 
pyroligneous  acid  by  agitating  the  liquid  with  3%  by  volume  of 
benzene. 

Pyroligneous  acid  differs  much  in  strength  according  to  the  kind 
and  state  of  division  of  the  wood  used  for  distillation,  and  is  also  affected 
by  the  construction  of  the  retorts.  Lopwood  yields  stronger  acid  and 
less  tarry  and  resinous  matters  than  spent  dye-woods  and  sawdust, 
even  though  of  the  same  kind. 

Pyroligneous  acid  from  finely-divided  wood  has  a  sp.  gr.  of  1.040 
to  1.045,  and  contains,  on  an  average,  about  4.5%  of  acetic  acid.  The 
product  of  the  distillation  of  lop-timber  contains  an  average  of  7.75% 
of  real  acid. 

The  strength  of  pyroligneous  acid  may  be  ascertained  by  titration 
with  standard  alkali  and  phenolphthalein,  but  the  liquid  is  frequently 
too  dark  in  colour  to  permit  of  the  end-reaction  being  readily  observed. 
Calcium  and  sodium  sulphates  and  acetates  are  frequently  present. 
In  the  absence  of  sulphates,  pyroligneous  acid  is  best  assayed  by  treat- 
ment with  excess  of  barium  carbonate,  with  estimation  of  the  dissolved 
barium  as  sulphate. 

Commercial  acetic  acid  ranges  in  strength  from  the  nearly  absolute 
glacial  acid  to  the  weakest  vinegar.  The  proportion  of  real  acetic  acid 
may  be  ascertained  by  the  methods  already  described :  in  certain  cases 
by  the  sp.  gr.;  and  in  the  case  of  glacial  acid  by  the  solidifying  point. 

The  assay  of  glacial  acetic  acid,  pyroligneous  acid  and  vinegar  is 
described  in  the  respective  sections  treating  of  these  products. 


ACETIC   ACID.  493 

Commercial  acetic  acid  is  often  prepared  by  distilling  sodium  or 
calcium  acetate  with  sulphuric  or  hydrochloric  acid.  It  is  liable  to 
contain  the  following  impurities: 

Sulphuric  acid  and  sulphates,  indicated  and  estimated  by  addi- 
tion of  barium  chloride,  which  in  their  presence  throws  down  white 
barium  sulphate. 

Sulphurous  acid,  indicated  by  adding  barium  chloride  in  excess, 
filtering  from  any  precipitate,  and  adding  bromine  water  to  the  clear 
nitrate.  An  additional  precipitate  of  barium  sulphate  indicates  the 
previous  presence  of  sulphurous  acid,  and  from  its  weight  the  amount  of 
impurity  can  be  calculated. 

Hydrochloric  acid  and  chlorides,  detected  and  estimated  by  addi- 
tion of  silver  nitrate. 

Copper  and  lead,  detected  by  evaporating  a  considerable  bulk  of 
the  sample  to  a  small  volume,  diluting  with  water,  adding  a  few  drops 
of  hydrochloric  acid,  and  passing  in  hydrogen  sulphide  which  produces 
a  black  or  brown  colouration  or  precipitate  in  presence  of  lead  or  cop- 
per. If  much  organic  matter  is  present,  the  evaporation  should  be 
carried  to  dryness  and  the  residue  ignited  in  porcelain.  The  heavy 
metals  are  then  sought  for  in  the  residue  in  the  manner  described  on 
page  63.  A  delicate  test  for  copper  is  the  red-brown  precipitate  or 
colouration  produced  by  potassium  ferrocyanide  in  the  original  liquid, 
or  the  same  concentrated  and  then  diluted  with  water.  If  iron  is  present 
in  such  quantity  as  to  give  a  blue  precipitate  and  thus  interfere  with  the 
reaction,  it  must  first  be  removed  by  addition  of  bromine  water  and 
excess  of  ammonia,  and  copper  sought  for  in  the  filtrate  after  acidify- 
ing with  acetic  or  hydrochloric  acid.  Samples  of  pickles  suspected 
to  be  coloured  with  copper  should  be  moistened  with  sulphuric  acid, 
ignited,  and  the  ash  dissolved  in  nitric  acid,  and  tested  in  acid  solu- 
tion with  potassium  ferrocyanide,  after  separation  of  the  iron  and 
phosphates  with  ammonia.  The  copper  can  be  determined  by  electro- 
deposition  on  the  inside  of  a  platinum  crucible  by  an  electric  current. 
Tin  and  zinc  have  been  occasionally  met  with  in  acetic  acid  and 
vinegar. 

Salts  of  calcium  are  detected  by  partially  neutralising  the  solution 
with  ammonia  and  adding  ammonium  oxalate,  which  will  produce  a 
white  precipitate  of  calcium  oxalate. 

Empyreumatic  and  indefinite  organic  bodies  may  be  detected  by 
exactly  neutralising  the  acid  with  sodium  carbonate  and  tasting  and 


494  ACID    DERIVATIVES    OF    ALCOHOLS. 

smelling  the  warmed  liquid.  The  neutralised  acid  gives  a  precipitate 
when  heated  to  boiling  with  ammonio-silver  nitrate,  and  the  original 
acid  darkens  when  heated  to  boiling  with  an  equal  measure  of  concen- 
trated sulphuric  acid,  if  the  above  impurities  are  present.  A  com- 
parative estimate  of  the  proportion  of  empyreumatic  impurities  pres- 
ent may  be  made  by  diluting  10  c.c.  of  the  sample  to  400  c.c.  .with 
water,  adding  hydrochloric  acid,  and  titrating  with  permanganate  till 
the  pink  colour  is  permanent  for  i  minute. 

Formic  acid  frequently  occurs  in  acetic  acid.  The  estimation  of  it 
has  been  investigated  by  H.  Ost  and  F.  Klein  (Chem.  Zeit.  1908,  32, 
815),  who  compared  several  processes,  such  as  neutralizing  with 
alkali  and  titrating  with  permanganate;  oxidising  with  standard 
chromic  acid  and  titrating  for  the  excess  of  this  acid;  treating  with 
mercuric  chloride  and  weighing  the  separated  metal.  These  methods 
are  fairly  accordant,  and  probably  in  absence  of  substances  (other 
than  formic  acid)  capable  of  reducing  permanganate,  the  per- 
manganate method  is  the  best.  (See  also  pp.  520  and  521).  Ost  and 
Klein  found  somewhat  over  0.5%  formic  acid  in  some  samples.  This 
cannot  be  removed  completely  by  distillation  or  by  direct  action  of 
potassium  permanganate  on  the  acid,  but  is  best  removed  by  crystal- 
lization. 

General  fixed  impurities  are  detected  and  estimated  by  evaporating 
of  a  known  measure  of  the  sample  to  dryness  and  weighing  the 
residue. 

Glacial  acetic  acid  (absolute  acetic  acid).  The  properties  of 
this  substance  have  been  already  described. 

Commercial  glacial  acetic  acid  should  contain  at  least  97%  of  the 
absolute  acid.  This  may  be  ascertained  by  agitating  i  volume  of  the 
sample  with  9  of  oil  of  turpentine.  Complete  solution  occurs  if  the 
strength  is  97%  or  above.  Samples  containing  99.5%  of  absolute  acid 
are  miscible  with  oil  of  turpentine  in  all  proportions.  Oil  of  lemon 
if  freshly  distilled,  may  be  employed  instead  of  turpentine. 

A  more  delicate  test  for  water  is  to  treat  the  sample  in  a  dry  test- 
tube  with  an  equal  measure  of  carbon  disulphide,  and  warm  the  mix- 
tnre  in  the  hand  for  a  few  minutes.  The  liquid  will  be  turbid  if  any 
water  is  present  in  the  sample. 

The  influence  of  water  on  the  m.p.  of  glacial  acetic  acid  is  shown 
in  the  following  table  by  Rudorff  (Pharm.  Jour.  [3],  1872,  2,  241) : 


VINEGAR. 


495 


Solidifying  point. 
°C. 

\Yater  to  100  parts 
:    of  real  C2H4O2. 

Solidifying  point. 

Water  to  100  parts 
of  real  C2H4O2. 

+  16.  70 
16.65 
14.80 
14.00 

0.0 

0.5 

I  .0 

6.25 
5-30 
4-3° 
3.60 

8.0 
9.0 

IO.O 
II  .0 

13  .  25 

2.0                                               2.70 

12  .O 

n-95 
10.50 
9.40 

8.20 

3-° 

4.0 

5-° 
6.0 

0.  20 
—  2.00 

-5-io 

—7.40 

18.0 

21.0 
24-0 

7.10, 

7-° 

The  strength  of  glacial  acetic  acid  may  also  be  ascertained  as  on 
page  490.  The  sp.  gr.  is  not  an  indication  of  value.  Impurities  may 
be  sought  for  as  on  page  502. 


Vinegar. 

Properly  speaking,  vinegar  is  a  more  or  less  coloured  liquid,  consist- 
ing essentially  of  dilute  acetic  acid,  obtained  by  the  oxidation  of  alcohol. 
Sometimes  the  term  is  improperly  extended  to  pyroligneous  acid,  or 
"wood  vinegar,"  while  acetic  acid  is  called  " distilled  vinegar."  In 
the  United  States,  vinegar  made  by  oxidising  dilute  alcohol  ;s  often 
called  "spirit"  vinegar,  and  as  the  dilute  alcohol  is  sometimes  called 
"low  wines"  the  vinegar  is  called  "wine"  vinegar,  but  such  a 
misleading  name  is  now  generally  forbidden  by  laws  against  mis- 
branding. 

The  reaction  between  alcohol  and  oxygen  takes  place  under  the 
influence  of  platinum-black  and  some  other  bodies,  but  the  formation 
of  vinegar  from  alcoholic  liquids  usually  depends  on  microorganisms. 
Mechanical  arrangements  are  employed  to  expose  a  large  surface  of 
the  alcoholic  liquid  to  the  air,  so  as  to  diminish  the  time  required  for 
acetification. 

Besides  acetic  acid,  vinegar  often  normally  contains  more  or  less 
of  other  organic  acids,  sugar,  dextrin  and  colouring  matters.  The 
agreeable  aromatic  smell  is  doubtless  due  to  esters,  and  is  sometimes 
imitated  by  direct  addition  of  ethyl  acetate. 

The  sp.  gr.  of  vinegar  is  of  no  value  as  an  indication  of  its  strength 
in  acetic  acid,  as  the  proportion  of  extractive  matter  differs  much  in 


496  ACID    DERIVATIVES    OF   ALCOHOLS. 

vinegar  from  various  sources.  The  " proof  vinegar"  of  the  (British) 
Excise  contains  about  5%  of  acetic  anhydride,  or  6%  of  the  absolute 
acid,  and  has  a  sp.  gr.  of  1.019.  By  the  manufacturer,  vinegars  of 
different  strengths  are  distinguished  by  the  number  of  grains  of  pure 
dry  sodium  carbonate  required  for  the  neutralisation  of  i  fluid  ounce. 
Thus  "proof  vinegar"  is  known  as  "No.  24,"  from  the  fact  that  24 
grains  are  required  for  the  neutralisation  of  i  ounce.  The  weaker 
qualities  are  Nos.  22,  20  and  18.  As  60  grains  of  absolute  acetic 
acid,  or  51  of  acetic  anhydride,  are  neutralised  by  53  of  sodium  car- 
bonate, the  number  of  grains  of  the  real  acid  contained  in  each  fluid 
ounce  of  the  vinegar  can  be  ascertained  by  multiplying  the  "number 
"  of  the  sample  by  J-f  =1.132.  If  the  "number"  is  multiplied  by  the 
factor  0.259,  the  product  will  be  the  parts  by  weight  of  absolute  acid  in 
100  measures  of  vinegar. 

Genuine  vinegar  of  good  quality  will  not  contain  much  less  than 
5%  of  absolute  acetic  acid,  though  something  depends  on  the  origin  of 
the  vinegar,  cider-vinegar  being  naturally  the  weakest  and  wine- 
vinegar  the  strongest  in  acetic  acid. 

The  proportion  of  acetic  acid  in  vinegar  may  be  ascertained  by  titra- 
tion  with  standard  caustic  alkali,  litmus-paper  or  phenolphthalein 
being  used  as  an  indicator.  Other  methods  are  described  on  page  490. 

Wine -vinegar  differs  in  colour  according  as  its  origin  is  white  or  red 
wine,  that  derived  from  the  former  being  most  esteemed.  It  contains 
from  6  to  12%  of  absolute  acetic  acid,  has  a  low  sp.  gr.  (1.014  to  1.022), 
and  an  extract  ranging  from  1.7  to  2.4%  (average  2.05).  If  the 
"extract"  or  residue  left  on  evaporation  is  treated  with  alcohol, 
nearly  everything  dissolves  except  a  granular  residue  of  crude  tartar, 
while  vinegars  made  from  malt  or  sugar  leave  a  more  or  less  glutinous 
residue,  only  sparingly  soluble  in  alcohol.  The  amount  of  "tartar" 
(potassium  hydrogen  tartrate)  contained  in  wine  vinegar  averages 
0.25%.  Its  presence  is  peculiar  to  wine-vinegar.  The  tartar  may  be 
proved  to  be  such  by  pouring  off  the  alcohol  and  dissolving  the  residue 
in  a  small  quantity  of  hot  water.  On  cooling  the  aqueous  solution  and 
stirring  the  sides  of  the  vessel  with  a  glass  rod,  potassium  hydrogen 
tartrate  will  be  deposited  in  streaks  in  the  track  of  the  rod.  An  ad- 
dition of  an  equal  bulk  of  alcohol  makes  the  reaction  more  delicate. 
Tartaric  acid  is  occasionally  added  to  vinegar  as  an  adulterant,  in 
which  case  the  residue  left  on  evaporation  at  a  steam  heat  is  viscous 
and  highly  acid.  By  treatment  with  proof-spirit  any  free  tartaric 


VINEGAR.  497 

acid  is  dissolved,  and  may  be  detected  in  the  solution  by  adding  a  so- 
lution of  potassium  acetate  in  proof  spirit  and  stirring  with  a  glass 
rod.  In  presence  of  tartaric  acid,  streaks  and  probably  a  distinct 
precipitate  of  potassium  hydrogen  tartrate  will  be  produced.  By 
titrating  the  precipitate  with  standard  alkali,  the  amount  of  free 
tartaric  acid  in  the  vinegar  can  be  determined. 

Cider-vinegar  is  yellowish,  has  an  odour  of  apples,  a  sp.  gr.  of  1.013 
to  0.115,  and  contains  3  1/2  to  6%  of  acetic  acid.  On  evaporation  to 
dryness  it  yields  from  1.5  to  1.8%  of  a  mucilaginous  extract,  smelling 
and  tasting  of  baked  apples,  and  containing  malic  but  no  tartaric  acid. 
Cider-vinegar  usually  gives  slight  precipitates  with  barium  chloride, 
silver  nitrate  and  ammonium  oxalate,  and  always  with  lead  acetate. 
Perry-vinegar  presents  similar  characters. 

The  frequent  imitation  of  cider-vinegar  by  a  mixture  of  acetic  acid 
and  water  with  addition  of  colouring  matter  (generally  caramel)  has 
led  to  much  investigation  as  to  the  means  of  detecting  the  fraud. 
Among  the  more  important  contributions  to  this  subject  are  papers  by 
Allen  and  Moor  (Analyst,  1893,  18,  240),  G.  S.  Cox  (Analyst,  1894, 
19,  89),  and  A.  W.  Smith  (/.  Ame.  Chem.  Soc.,  1898,  20,  3).  Cox 
gives  the  analytic  results  on  20  samples  of  cider-vinegar  and  4  sam- 
ples of  unfermented  cider.  The  acidity  of  the  vinegar  ranged  from 
2.28%  to  8.4%,  the  solids  from  1.34%  to  4.0%,  the  ash  from  0.25  to 
0.52.  By  recalculating  these  results  by  Hehner's  rule  it  is  found  that 
the  proportion  of  original  solids  of  the  juice  ranged  from  5.51%  to 
16.00%  and  the  ash  from  1.94%  to  4.88%. 

The  distinction  between  unadulterated  cider-vinegar  and  the  imita- 
tion made  by  adding  colouring  matter  to  dilute  acetic  acid  can  be 
easily  made.  The  latter  preparation  leaves  but  little  solid  residue, 
almost  no  ash,  and  has  but  little  flavour. 

A.  W.  Smith  finds  that  the  ash  of  cider-vinegar  differs  from  that  of 
most  other  vinegars  in  the  following  important  points: 

It  commences  to  melt  and  volatilise  at  a  comparatively  low  tempera- 
ture and  gives  to  flame  the  potassium  tint  unobscured  by  that  of 
sodium.  It  is  low  in  chlorides  and  sulphates  and  high  in  carbonates 
and  phosphates;  about  2/3  of  the  phosphates  are  soluble  in  water.  In 
the  ash  of  other  vinegars  a  much  lower  proportion  of  phosphates  is 
soluble  in  water.  The  dilution  of  vinegar  by  natural  water  will  be  apt 
to  reduce  the  soluble  matter  by  the  formation  of  calcium  and  mag- 
nesium phosphate. 
VOL.  1—32 


49$  ACID    DERIVATIVES    OF    ALCOHOLS. 

Beer-  and  malt-vinegars  have  a  high  sp.  gr.  (1.021  to  1.025)  and 
yield  5  to  6%  of  extract,  containing  a  notable  proportion  of  phosphates. 
The  acetic  acid  varies  from  3  to  6%.  Barium  chloride  and  silver 
nitrate  frequently  give  considerable  precipitates,  owing  to  the  pres- 
ence of  sulphates  and  chlorides  in  the  water  used  in  the  manufacture. 
Some  manufacturers  color  spirit  vinegar  (see  above)  by  soaking  dark 
malt  in  it  and  designate  the  product  as  "malt-vinegar. 

Glucose-  or  sugar-vinegar  is  now  extensively  prepared  from 
amylaceous  materials  by  conversion  with  dilute  acid,  followed  by  fer- 
mentation and  acetification.  Glucose-vinegar  usually  contains  dex- 
trose, dextrin  and,  very  often,  calcium  sulphate  (see  page  378).  Hence 
it  reduces  Fehling's  solution  and  usually  gives  abundant  precipitates 
with  barium  chloride  and  ammonium  oxalate,  and  frequently  with 
silver  nitrate  also.  When  mixed  with  3  or  4  times  its  volume  of  strong 
alcohol,  glucose-vinegar  gives  a  precipitate  of  dextrin.  It  is  best  to  con- 
centrate the  sample  before  applying  this  test.  Dextrose  is  best  de- 
tected and  estimated  by  evaporating  50  c.c.  of  the  sample  to  a  syrup 
and  adding  alcohol.  The  liquid  is  filtered,  decolourised  by  boiling  with 
animal  charcoal,  again  filtered,  the  alcohol  boiled  off  and  the  dextrose 
estimated  by  Fehling's  solution. 

Vinegar  may  be  made  by  diluting  acetic  acid  to  suitable  strength, 
colouring  with  burnt  sugar,  and  flavouring  with  a  little  acetic  ether. 
Such  a  product  differs  from  malt-vinegar  by  containing  no  phosphates, 
and  from  wine-  and  cider-vinegars  in  the  absence  of  tartaric  acid  and 
malic  acid,  respectively. 

Hehner  regards  the  presence  of  ^aldehyde  and  alcohol,  causing  an 
abundant  iodoform  reaction  in  the  distillate  from  the  neutralised 
sample,  as  evidence  of  fermentation,  and  that  the  sample  is  true 
vinegar.  Vinegar  made  from  sugar  contains  hardly  any  proteids,  while 
that  from  malt  contains  about  0.7%.  Vinegar  prepared  by  acid  inver- 
sion of  starches  usually  contains  a  high  ash  with  sulphates.  The  ash  of 
cane-sugar  vinegar  is  readily  fusible;  that  of  a  malt  or  a  glucose  vinegar 
does  not  readily  fuse.  Sugar-vinegar  yields  an  ash  composed  mainly 
of  potassium  salts,  as  raw  cane-sugar  is  employed,  not  refined  sugar. 
The  estimation  of  potassium  with  a  view  to  prove  the  presence  of 
grain  vinegar  is  useless,  since  both  grain  and  raw  sugar  contain  much 
potassium. 

Alcohol  always  exists  in  a  well-made  fermentation  vinegar,  for 
manufacturers  stop  the  process  before  the  acetification  is  complete. 


VINEGAR.  499 

Vinegar  may  diminish  in  strength  to  the  extent  of  fully  i%  of  acid  in 
6  months.  If  the  alcohol  is  all  destroyed  the  change  is  likely  to  be 
much  more  rapid.  Vinegar  should  contain  alcohol  not  only  for  keep- 
ing purposes,  but  to  insure  a  gradual  formation  of  acetic  ether,  just 
the  same  as  in  wine  after  keeping.  Fermentation  vinegar  might  be 
distinguished  in  that  way,  but  it  is  easy  to  add  alcohol  to  imitate  a  fer- 
mentation vinegar.  Some  manufacturers  add  acetic  ether.  There  is 
a  considerable  amount  of  solid  extract  in  fermentation  vinegar,  but 
in  a  mixture  containing  pyroligneous  acid  the  quantity  is  much  less. 
The  solid  matter  differs  much  according  to  the  perfection  of  the  fer- 
mentation, and  affords  an  indication  of  some  value,  though  not  so 
great  as  the  amount  of  ash,  which  does  not  change  to  a  great  extent 
through  the  fermentation.  The  proportion  of  sulphates  will  afford 
some  information  as  to  the  probable  use  of  glucose.  The  estimation 
of  total  nitrogen  is  a  valuable  criterion.  Grain  vinegars  contain  a 
notable  amount  of  nitrogen,  although  the  manufacturers  attempt  to 
remove  nitrogenous  matters.  In  estimating  the  total  nitrogen  by  the 
Kjeldahl  method,  the  vinegar  is  evaporated  to  dryness,  or  at  any  rate 
to  a  syrup,  before  adding  the  sulphuric  acid.  25  c.c.  of  vinegar  is  a 
convenient  quantity  to  employ.  The  nitrogen  found  can  then  be  cal- 
culated to  its  equivalent  of  proteins  by  the  usual  factor;  but  probably 
much  of  the  organic  nitrogen  of  vinegar  exists  in  other  forms.  In  one 
case  Allen  found  10%  of  the  nitrogen  as  ammonium  salts.  The  pro- 
portions of  all  constituents  will  differ  with  the  strength  of  the  vinegar. 
A  wort  which  originally  contained  12%  of  sugar  and  other  solids  will 
contain  more  nitrogen,  ash  and  phosphates  than  a  vinegar  which 
originally  contained  only  7%  of  sugar.  Therefore,  it  is  desirable  to 
adopt  Hehner's  plan  of  calculating  the  various  constituents  upon  the 
original  solids  of  the  vinegar;  60  parts  of  acetic  acid  are  theoretically 
produced  from  90  of  glucose,  and  hence,  if  the  acetic  acid  found  be 
multiplied  by  1.5,  we  obtain  the  amount  of  sugar  from  which  that 
acetic  acid  was  derived.  Adding  to  the  figure  thus  obtained  the  total 
extractive  matters  still  contained  in  the  vinegar,  we  obtain  a  number 
representing  the  "original  solids"  of  the  wort.  Thus,  if  a  vinegar 
contain  5.2%  of  acetic  acid  and  2.8  of  extract,  the  original  solids  will 
be  7.8  +  2.8  =  10.6.  If  the  vinegar  itself  contained  0.08  of  nitrogen, 
the  original  solids  will  contain — 

0.08X100 


5oo 


ACID    DERIVATIVES    OF   ALCOHOLS. 

X 


8n    M  1)0) 

.2°  £§ 

t^oo      iicooo       ocoo 


o 
w 


o 

C/3 


PH 

a 

CO 


O 

h-t 
PH 


o  : 

*°i 

sS 

a  e 


w 

fe 

o 

to 

H 

p 

CO 

W 

P< 

fe 

O 

CO 
— 
CO 

PL, 
O 
z 

>H 

CO 


o"  &  «  o 


•<t  o  o      -So 


M 


00 

(N  VO    J>- 
ON  *>•  W 

Tf    H     O 


oooo 
o  TJ-OO 


"*    H     N     t^. 

H    io  vo  CS  OOOOOO 

•  co  H  d  ddddvd 
6  rF^ ~~o 


vo  «   o 

-<tNoCl>. 
O    «   vovo 


O  CO   tN.    'tf    VO 

ONOO  OOO          MMOVOVO        rfvo  rovo 

MVOONCO  OOMVOfO          \O     M     ONOO 


O 


0  O   O   O    w 

1  ^vS^ 


vo 


O  rh  W  OO 

CO  N  vO    O  f>vO    vo  W 

H    (N   vo  co  00 

O     •     •      •  

•VOHO  OOOOON 


ON 
fO 


w 


u 


rf  vo 

I     ro  O    t         WO 
I      N    t^.  CO 


O     M 

d  d 


vo        -^-vo 

CO          VO     M 

O\        tO  M 


VO  VO      M 
MOO     *> 


I     O    O  vo  vo 

I    o  o  d  ds 

"00~  "fO^lOOO 
H    0s  QN  QN  vo 
H    O    O    vooO 


ONO 
t^OO 


?? 

d       do 


vo    <N    0 


N  vo    O 

O  O     CN 
H     O     H 


s 


a 

ju 

"H^ 

I 


>^'n      '  — 

°-s^  ;  ;s 

—     OH     .       .^_ 


C 

1 


g> 


3     a 

CO  ^ 

a 

§'s    ^ 


I 

§ 

1 


S? 


^ 


^^ 

o  ii 


O  M-t 

cn    O    cu 
Q 


.ilT) 

3*eg 


3  S 


±i  a 

Q 


II 


-    >> 


CU  O  H-l 


S!  b§^ 
^  &>  a 

t^  s    ^ 


W  fa 


o 
p^ 


VINEGAR.  501 

In  this  manner  one  can  eliminate  the  differences  caused  by  irregu- 
larity in  the  strength  of  various  samples  of  vinegar  and  reduce  the 
results  to  a  kind  of  common  denominator.  As  a  matter  of  fact,  the 
loss  of  acetic  acid  in  the  process  of  manufacture  averages  some  30%, 
so  that  the  proportion  of  original  solids  calculated  in  the  above  manner 
is  always  below  the  truth.  Hence  a  nearer  approximation  to  accuracy 
would  be  obtained  by  multiplying  the  acetic  acid  by  2.25,  instead  of  1.5, 
before  adding  the  extract,  but  the  change  would  involve  confusion,  and 
it  is  best  to  adhere  to  the  mode  of  calculation  originally  suggested  by 
Hehner. 

Wood  vinegar  is  a  name  sometimes  applied  to  pyroligneous  acid. 

Aromatic  vinegar  is  a  product  obtained  by  distilling  a  metallic 
acetate,  usually  crystallised  cupric  acetate.  The  presence  of  acetone 
and  other  bodies  imparts  an  agreeable  aroma.  A  small  addition  of 
camphor  or  essential  oil  is  often  made. 

Mineral  Acids  in  Vinegar. — Very  weak  vinegar  is  liable  to  a  putrid 
fermentation,  to  prevent  which  the  addition  of  i  gallon  of  sulphuric 
acid  to  1000  gallons  of  vinegar  (about  0.185%)  was  permitted  by  a 
British  Excise  regulation.  This  addition  is  now  known  to  be  unneces- 
sary with  good  vinegar  and  is  abandoned  by  the  best  makers,  though 
the  practice  is  not  obsolete,  and  the  legal  proportion  of  sulphuric  acid 
has  been  occasionally  largely  exceeded.  In  addition  to  sulphuric  acid, 
hydrochloric  acid  has  been  occasionally  added  to  vinegar,  but  the 
adulteration  of  vinegar  with  mineral  acids  is  now  very  rarely 
practised. 

For  detecting  mineral  acids  in  vinegar  several  tests  have  been  de- 
vised, but  the  most  are  either  untrustworthy  or  deficient  in  delicacy. 
Some  are  applicable  to  the  detection  of  sulphuric  acid  only,  whilst 
others  include  hydrochloric  and  other  mineral  acids  also.  The  em- 
ployment of  barium  chloride  and  silver  nitrate  for  the  detection  of 
sulphuric  and  hydrochloric  acids,  respectively,  has  led  several  analysts 
into  error,  owing  to  the  presence  naturally  of  sulphates  and  chlorides  in 
the  water  employed  in  the  manufacture  of  the  vinegar. 

Another  circumstance  which  complicates  the  problem  is  that  the 
addition  of  a  mineral  acid  in  moderate  quantity  merely  decomposes 
the  acetates  naturally  present  in  the  vinegar,  with  liberation  of  acetic 
acid  and  formation  of  sulphates  or  chlorides.  Hence,  only  the  acid 
beyond  that  required  for  the  decomposition  of  the  acetates  can  exist 
in  the  free  state,  and  to  the  presence  of  such  free  mineral  acids  only 


502  ACID    DERIVATIVES    OF    ALCOHOLS. 

can  objection  reasonably  be  taken,  unless  the  mineral  acid  used  is 
contaminated  with  arsenic. 

Acetates  and  most  other  salts  of  organic  acids  decompose  by  ignition 
into  carbonates,  having  an  alkaline  reaction  to  litmus,  while  sulphates 
and  chlorides  of  the  lighter  metals  are  unchanged  on  ignition  and  pos- 
sess a  neutral  reaction.  Hence,  if  the  ash  of  a  vinegar  has  a  sensibly 
alkaline  reaction,  acetates  must  have  been  present  in  the  original  vinegar 
and  no  free  sulphuric  or  hydrochloric  acid.  To  determine  the  amount 
of  free  mineral  acid  it  is  sufficient  to  neutralise  the  vinegar  with  stand- 
ard sodium  hydroxide  before  evaporation  to  dryness  (the  same  process 
serves  for  a  determination  of  the  total  free  acid),  ignite  the  residue,  and 
titrate  the  aqueous  solution  of  the  ash  with  standard  acid.  If  the  free 
acid  originally  present  was  wholly  organic,  the  ash  will  contain  an 
equivalent  amount  of  alkaline  carbonate,  which  will  require  an  amount 
of  standard  acid  for  its  neutralisation  exactly  equivalent  to  the  amount 
of  standard  alkali  originally  added  to  the  vinegar.  Any  deficiency  in 
the  amount  of  standard  acid  required  for  neutralisation  is  due  to  the 
free  mineral  acid  originally  present  in  the  vinegar.  More  accurate 
results  are  obtained  if  the  amount  of  standard  alkali  added  before 
evaporation  is  insufficient  for  the  complete  saturation  of  the  acetic  acid, 
but  more  than  enough  for  the  neutralisation  of  all  mineral  and  fixed 
organic  acids  which  may  be  present.  By  thus  proceeding,  decinormal 
alkali  and  acid  may  be  employed  (50  c.c.  of  the  vinegar  being  used), 
and  thus  sharper  readings  obtained. 

The  total  chlorine,  existing  as  chlorides,  cannot  be  ascertained  in 
vinegar  by  direct  precipitation  with  silver  nitrate.  For  a  correct  assay, 
50  c.c.  of  the  vinegar  should  be  neutralised  with  alkali,  evaporated 
to  dryness,  the  residue  ignited,  dissolved  in  water,  and  the  aqueous 
solution  precipitated  with  excess  of  calcium  sulphate  or  nitrate  to 
remove  phosphates.  The  filtrate  from  this  precipitate  may  be  pre- 
cipitated by,  or  titrated  with  a  solution  of  silver  nitrate. 

The  sulphuric  acid  and  sulphates  may  be  precipitated  by  the  direct 
addition  of  barium  chloride  to  the  diluted  vinegar,  but  the  figure  has 
little  value. 

Free  sulphuric  acid,  as  distinguished  from  sulphates,  may  be  esti- 
mated with  considerable  accuracy  by  evaporating  100  c.c.  of  the  vinegar 
to  a  small  bulk  and  then  adding  to  the  cold  concentrated  liquid  4  or  5 
times  its  volume  of  alcohol.  Sulphates  are  precipitated,  while  free 
sulphuric  acid  remains  in  solution.  The  filtered  liquid  is  diluted, 


VINEGAR.  503 

the  alcohol  boiled  off  and  the  sulphuric  acid  precipitated  with  barium 
chloride.  The  precipitate  is  filtered  off,  washed,  dried,  ignited  and 
wi-ighed.  Its  weight,  multiplied  by  0.4206,  gives  the  weight  of  sul- 
phuric acid  in  the  quantity  of  vinegar  taken.  In  a  vinegar  free  from 
chlorides  this  process  gives  results  in  accordance  with  Hehner's  proc- 
ess, but  in  their  presence  the  mineral  acid  found  is  deficient  by  the 
amount  of  sulphuric  acid  required  to  decompose  the  chlorides. 
This  difficulty  may  be  obviated  by  treating  the  vinegar  with  excess  of 
silver  sulphate  solution  before  evaporation,  by  which  treatment  any 
free  hydrochloric  is  also  estimated  as  sulphuric  acid. 

An  ingenious  method  of  detecting  jree  sulphuric  acid  in  vinegar  and 
wine  has  been  described  by  Casali.  20  grm.  weight  of  the  sample 
is  ground  up  in  a  mortar  with  about  80  grm.  of  finely  powdered 
porcelain  (previously  treated  with  hydrochloric  acid  to  remove  every 
trace  of  free  alkali),  so  that  the  mixture  is  not  moist  to  the  touch.  The 
whole  is  then  ground  up  with  50  c.c.  of  ether  (previously  agitated  with 
magnesia  and  water  to  neutralise  any  trace  of  acid),  filtered  and 
washed  with  ether.  The  filtrate  is  then  shaken  with  a  little  distilled 
water,  the  ether  distilled  off  and  the  residue  precipitated  with  barium 
chloride;  0.0005  grm.  of  free  sulphuric  acid  can  be  readily  detected 
by  this  method. 

A  very  simple,  and  apparently  reliable  method  of  detecting  free 
mineral  acids  in  vinegar  has  been  described  by  A.  Ashby.  A  solution 
of  logwood  is  prepared  by  pouring  100  c.c.  of  boiling  water  on  about 
2  grm.  of  fresh  logwood  chips,  and  then  allowing  the  decoction  to 
stand  for  a  few  hours.  Separate  drops  of  this  solution  are  spotted  on 
the  surface  of  a  flat  porcelain  dish  or  on  the  cover  of  a  porcelain 
crucible,  and  evaporated  to  dryness  over  a  beaker  of  boiling  water. 
To  each  spot  a  drop  of  the  suspected  sample  (previously  concentrated, 
if  thought  desirable)  should  be  added,  and  the  heating  continued  till 
the  liquid  has  evaporated.  If  the  vinegar  is  pure  the  residue  will 
be  found  to  have  a  bright  yellow  colour,  but  in  presence  of  a  very  small 
proportion  of  mineral  acid  the  residue  assumes  a  red  colour. 

If  the  proportion  of  mineral  acid  is  very  small,  the  red"  colour  is 
destroyed  on  adding  water  to  the  residue,  but  is  restored  on  evapo- 
rating, except  in  the  case  of  nitric  acid. 

Tartaric  acid  in  vinegar  may  be  detected  as  described  under  Wine- 
vinegar,  of  which  it  is  a  normal  constituent. 

Oxalic  acid  may  be  detected  by  evaporating  20  c.c.  of  the  vinegar 


504  ACID    DERIVATIVES    OF   ALCOHOLS. 

to  a  small  bulk,  diluting  the  residue  with  water,  and  adding  calcium- 
acetate  solution  or  a  mixture  of  ammonium  acetate  and  calcium  chloride. 
Any  oxalic  acid  causes  the  formation  of  white  calcium  oxalate. 

Arsenic  has  been  occasionally  met  with  in  vinegar,  and  may  be 
introduced  by  the  addition  of  impure  hydrochloric  or  sulphuric  acid. 
It  may  readily  be  detected  by  Marsh's  or  Reinsch's  test. 

Lead  and  copper  may  be  detected  as  described  on  pages  63  and  569. 

Zinc  is  occasionally  present  in  vinegar.  It  may  be  detected  by 
boiling  down  the  vinegar  to  dryness  with  nitric  acid,  dissolving  the 
residue  in  acidulated  water,  passing  hydrogen  sulphide,  filtering  from 
any  precipitate  and  then  adding  ammonium  acetate,  when  white  zinc 
sulphide  will  be  thrown  down  if  the  metal  is  present.  A  less  satisfac- 
tory method  is  to  neutralise  the  greater  part  of  the  free  acid  in  the 
original  vinegar  by  ammonia,  and  then  at  once  passing  in  hydrogen 
sulphide. 

Cayenne  pepper  and  ginger,  are  sometimes  added  to  vinegar  to 
confer  pungency.  They  may  be  detected  by  neutralising  the  concen- 
trated vinegar  with  sodium  carbonate  and  tasting  the  liquid. 

Flies  and  so-called  "eels"  are  often  found  in  vinegar.  They  are 
readily  detected  by  the  microscope,  and  may  be  destroyed  by  raising 
the  temperature  of  the  liquid  to  100°. 

Analysis  of  Commercial  Vinegar. — The  following  is  a  summary 
of  some  of  the  processes  provisionally  suggested  by  the  Association  of 
Official  Agricultural  Chemists,  and  published  by  the  United  States 
Bureau  of  Chemistry,  Washington,  D.  C.  (Bulletin  107,  United 
States  Department  of  Agriculture). 

Microscopic  examination  should  be  made  of  the  sediment,  but  the 
sample  for  chemical  examination  should  be  filtered  and  tested  as  soon 
as  possible.  All  results  are  expressed  by  weight,  but  c.c.  are  regarded 
as  equivalent  to  grm.  in  routine  testing.  The  sp.  gr.  is  determined  in 
the  usual  way. 

Alcohol. — 100  c.c.  are  exactly  neutralized  with  sodium  hydroxide 
and  40  c.c.  distilled.  The  distillate  is  redistilled  until  20  c.c.  are 
collected.  This  distillate  is  cooled  to  15.5°,  made  up  to  20  c.c.  and 
the  alcohol  ascertained  in  the  usual  way. 

Total  Solids. — 10  c.c.  are  evaporated  to  syrupy  consistence,  then 
dried  in  an  oven  for  2  1/2  hours,  cooled  and  weighed. 

Ash. — This  is  determined  in  the  usual  way  from  the  above  residue. 

Alkalinity  and  Solubility  of  Ash. — 25  c.c.  of  the  sample  are 


VINEGAR.  505 

ashed,  extracted  repeatedly  with  hot  water,  collecting  the  undissolved 
material  by  passing  the  water  through  an  ashless  filter.  The  water 
solution  is  titrated  with  N/io  acid  and  methyl-orange.  The  filter 
is  dried,  burned  and  the  residue  weighed. 

Phosphoric  Acid. — This  is  ascertained  in  both  the  water-soluble 
and  insoluble  portions  of  the  ash  by  the  standard  methods  of  fertiliser 
analysis. 

Total  Acidity. — A  suitable  amount  diluted  until  it  has  no  inter- 
fering colour  is  titrated  with  N/io  alkali  using  phenolphthalein  as 
indicator.  One  c.c.  of  the  alkali  is  equivalent  to  0.0060  acetic  acid. 

Volatile  Acids. — 15  c.c.  are  heated  to  boiling  in  a  flask,  using  a 
little  tannin  if  necessary  to  prevent  foaming.  The  flame  is  then  lowered 
and  a  current  of  steam  passed  through,  and  continued  until  15  c.c. 
of  the  liquid  in  the  condenser  show  no  acidity  with  sensitive  litmus- 
paper.  The  combined  distillate  is  titrated  for  total  volatile  acids. 

Fixed  Acids. — The  figure  for  volatile  acids  is  deducted  from  that 
for  total  acids;  the  remainder  multiplied  by  0.817  wiN  giye  sulphuric 
acid,  or,  by  1.117,  malic  acid.  If  tannin  has  not  been  added,  the 
undistilled  portion  may  be  directly  titrated  with  N/io  acid.  One 
c.c.  of  this  is  equivalent  to  0.0049  sulphuric  acid  or  0.0067  malic  acid. 

Potassium  Hydrogen  Tartrate. — Use  the  method  on  page  545. 

Tartaric  Acid. — Treat  an  alcoholic  solution  of  the  residue,  obtained 
as  directed  in  the  immediately  preceding  process,  with  an  alcoholic  solu- 
tion of  potassium  acetate  and  stir  mixture  with  a  glass  rod,  drawing 
the  latter  along  the  sides  of  the  beaker.  Crystals  of  acid  potassium 
tartrate  will  separate  if  tartaric  acid  is  present.  Approximate  quan- 
titative results  may  be  obtained  by  titrating  this  precipitate  with 
standard  alkali. 

Mineral  Acids. — For  the  logwood  method  see  page  503.  Another 
method  is  as  follows:  5  c.c.  of  the  sample  are  diluted  with  10  c.c. 
of  water,  then  a  few  drops  of  a  solution  of  methyl -violet  (i  part  of  colour 
to  10,000  of  water)  are  added.  If  the  liquid  becomes  blue  or  green, 
mineral  acid  is  present. 

The  amount  of  mineral  acid  ascertained  is  by  Hilger's  method: 
20  c.c.  are  exactly  neutralised  with  N/2  alkali,  using  sensitive  (neutral) 
litmus-paper  as  the  indicator.  The  liquid  is  evaporated  to  i/io  its 
volume,  a  few  drops  of  the  dilute  solution  of  methyl-violet  added  (see 
above)  and,  if  the  liquid  is  not  clear,  a  few  c.c.  of  water  added,  then 
titrated  with  N/2  sulphuric  acid  until  the  solution  becomes  green  or 


506  ACID    DERIVATIVES    OF   ALCOHOLS. 

blue.  The  difference,  in  c.c.,  between  the  N/2  alkali  required  and  the 
N/2  acid  required  multiplied  by  0.1225  expresses  the  mineral  acid 
present  in  terms  of  sulphuric  acid. 

Acetates. — Many  of  these  are  extensively  used  in  the  arts  and 
medicine.  Their  analytical  characters  and  the  general  methods 
adopted  for  their  assay  have  been,  in  great  measure,  already  described. 
The  following  observations,  therefore,  have  reference  chiefly  to  the  de- 
tection of  impurities  and  adulterations  in  commercial  acetates.  Sections 
treating  of  acetic  esters  and  acetates  containing  nitrogenous  bases  will 
be  found  in  other  parts  of  this  work. 

Potassium  Acetate,  KC2H3O2. — This  exists  in  some  vegetable 
secretions.  It  is  deliquescent,  very  soluble  in  water  and  alcohol  and 
neutral  to  litmus.  It  fuses  at  incipient  redness,  and  at  a  higher  tem- 
perature decomposes,  leaving  potassium  carbonate.  The  amount 
of  acetate  present  in  commercial  samples  may  be  ascertained  by  the 
general  methods  given  on  page  509. 

Commercial  potassium  acetate  is  liable  to  contain  sulphates, 
chlorides  and  carbonates;  iron,  lead,  copper  and  zinc;  arsenic  is 
occasionally  present.  It  is  sometimes  intentionally  adulterated,  cal- 
cium acetate  and  potassium  sulphate,  potassium  tartrate  or  potassium 
carbonate  being  employed. 

Potassium  acetate  being  soluble  in  alcohol,  any  admixture  of  sul- 
phates, tartrates  or  carbonates  may  be  detected  and  estimated  by 
treatment  with  that  solvent.  Carbonate  is  indicated  more  precisely 
by  alkaline  reaction;  precipitation  by  chloride  of  calcium;  power  of 
decolorising  iodised  starch;  and  effervescence  on  adding  an  acid. 

Sodium  acetate,  NaC2H3O2,  closely  resembles  the  potassium  salt, 
but  crystallises  with  3  molecules  of  water.  It  is  liable  to  contain  the 
same  foreign  matters  as  potassium  acetate.  Crude  sodium  acetate 
often  contains  tarry  matters  derived  from  the  pyroligneous  acid  em- 
ployed in  its  preparation.  Its  supersaturated  solution  has  been  used 
for  filling  foot-warmers. 

Ammonium  Acetate,  (NH4)C2H3O2. — This  salt  is  generally  met 
with  in  solution,  but  may  be  obtained  in  the  solid  state,  when  it  is 
apt  to  contain  acetamide. 

Ammonium  acetate  is  liable  to  contain  much  the  same  impurities  as 
the  potassium  salt,  and  may  be  examined  in  a  similar  manner.  It 
should  be  wholly  volatile  on  ignition. 


VINEGAR.  507 

Calcium  Acetate,  Ca(C2H3O3)2.— This  crystallises  with  diffi- 
culty in  prismatic  needles  containing  i  molecule  of  water.  It  is  de- 
composed by  heat  into  acetone,  and  calcium  carbonate. 

Calcium  acetate  should  be  completely  soluble  in  water  and  in  proof 
spirit.  An  insoluble  residue  may  consist  of  calcium  sulphate  or  carbon- 
ate. The  solution  should  give  no  precipitate  with  silver  nitrate  or 
barium  chloride.  Potassium  ferrocyanide  colours  the  solution  blue  if 
the  sample  contains  iron,  and  brown  if  copper  is  present. 

Assay  of  "Acetate  of  Lime." — This  is  the  commercial  name  for 
calcium  acetate  obtained  from  crude  pyroligneous  acid.  It  is  often  very 
impure,  containing  tarry  matter;  calcium  hydroxide,  carbonate  and 
sulphate  and  salts  of  the  homologues  of  acetic  acid.  Its  assay  is  of 
importance  and  somewhat  difficult.  If  the  salt  is  ignited,  and  the 
amount  of  acetic  acid  calculated  from  the  weight  of  the  residual 
calcium  carbonate  or  from  the  amount  of  normal  acid  the  residue 
will  neutralise,  very  erroneous  results  may  be  obtained. 

Calcium  formate  has  been  found  in  crude  acetate,  the  proportion 
sometimes  reaching  4  or  5%.  When  operating  on  the  large  scale,  the 
presence  of  formates  is  unmistakable.  On  crystallising  out  sodium 
acetate  as  completely  as  possible,  a  dense  syrupy  liquid  is  left  which 
contains  sodium  formate,  reduces  silver  and  mercuric  salts,  and  evolves 
carbon  monoxide  when  treated  with  excess  of  sulphuric  acid. 

A  method  of  assay,  much  used  in  the  neighborhood  of  Manchester, 
England,  has  been  described  by  H.  Grimshaw:  10  grm.  of  the 
sample  of  crude  acetate  are  dissolved  in  boiling  water,  and  20  grm. 
of  crystallised  sodium  sulphate  added.  The  liquid  is  raised  to  boil- 
ing, cooled,  diluted  to  250  c.c.,  and  allowed  to  stand  for  12  hours. 
The  calcium  will  then  have  separated  as  crystalline  calcium  sulphate. 
The  liquid  is  filtered,  the  precipitate  washed  with  hot  water,  and  the 
filtrate  made  up  to  500  c.c.  50  c.c.  of  this  solution  (  =  i  grm.  of  the 
sample)  should  then  be  evaporated  to  dryness  at  100°,  and  somewhat 
further  dried  in  an  air-bath.  The  residue  is  ignited  at  a  red  heat  over 
a  good  bunsen  burner  for  half  an  hour,  allowed  to  cool,  and  treated 
with  10  c.c.  of  N/i  hydrochloric  acid,  using  a  cover  to  avoid  loss. 
The  solution  is  boiled  well  to  drive  off  carbon  dioxide,  filtered,  the 
residual  carbon  washed,  and  the  filtrate  titrated  with  decinormal 
sodium  hydroxide,  using  methyl-orange  or  litmus  as  an  indicator. 
Each  c.c.  of  normal  acid  found  to  have  been  neutralised  by  the  ash 
represents  0.060  grm.  of  acetic  acid  (C2H4O2),  or  0.079  grm-  °f  calcium 


508  ACID    DERIVATIVES    OF   ALCOHOLS. 

acetate,  in  the  liquid  ( =  i  grm.  of  the  sample)  evaporated.  Great  care 
is  requisite  in  conducting  the  titration,  as  a  very  small  difference  in 
the  volume  of  alkali  required  makes  a  sensible  change  in  the  result. 
The  portion  of  the  sample  taken  for  the  analysis  should  be  finely 
powdered,  and  if  the  solution  in  water  be  appreciably  acid  it  should 
be  cautiously  neutralised  with  sodium  hydroxide  before  adding  the 
sodium  sulphate.  Grimshaw  found  this  process  to  give  results  rang- 
ing from  close  agreement  to  about  2%  in  excess  of  those  obtained 
from  the  same  samples  by  distillation  with  phosphoric  acid.  The 
results  are  not  vitiated  by  the  presence  of  calcium  carbonate  or  other 
insoluble  calcium  compounds  in  the  sample. 

Allen  found  a  tendency  to  incomplete  decomposition  of  the  acetate 
if  too  low  a  temperature  is  employed.  He  suggested  to  evaporate 
a  measure  of  solution  representing  5  grm.  of  the  sample,  and 
ignite  at  a  moderate  red  heat  in  a  muffle,  subsequently  moistening 
-the  ash  with  hydrogen  peroxide  to  oxidise  any  sulphides  which  may 
have  been  formed. 

The  distillation  process  given  in  the  preceding  edition  of  this 
work  was  communicated  by  Still  well  and  Gladding,  being  an  im- 
provement on  the  process  published  previously  by  them.  A  further 
communication  by  Stillwell  will  be  found  in  /.  Soc.  Chem.  Ind.,  1904, 
23>  3°5-  The  following  process,  essentially  the  same,  is  given  by 
H.  C.  Sherman  (Methods  of  Organic  Analysis)  as  now  in  general  use. 
For  an  extended  account  of  methods  of  assaying  commercial  calcium 
acetate,  see  a  paper  by  Grosvenor  in  /.  Soc.  Chem.  Ind.,  1904,  23,  530. 

A  300  c.c.  flask  is  fixed  at  an  angle  of  about  60°  from  the  perpen- 
dicular and  connected  with  a  nearly  vertical  condenser  while  another 
tube  passing  through  the  stopper  of  the  flask  provides  for  the  intro- 
duction of  water,  drop  by  drop,  during  distillation.  The  flow  of 
water  should  be  under  complete  control.  The  weighed  material 
(2  grm.)  finely  ground  is  transferred  to  the  flask,  15  c.c.  of  50%  phos- 
phoric acid  and  25  c.c.  of  water  added,  taking  care  that  the  water 
washes  down  any  powder  or  acid  that  is  in  the  neck  of  the  flask.  The 
apparatus  is  connected  and  the  distillate  collected  in  a  receiver  con- 
taining 50  c.c.  of  water.  During  the  process,  the  volume  of  the  liquid 
.should  be  kept  at  40  c.c.  as  near  as  may  be,  by  admitting  water  free 
from  carbonic  acid,  adding  it  so  that  the  drops  fall  on  the  side  of  the 
flask  and  not  directly  into  the  discilling  liquid.  It  is  stated  that  it  is 
.advantageous  to  use  water  containing  a  little  phosphoric  acid.  The 


VINEGAR. 


operation  is  continued  until  the  distillate  is  no  longer  acid,  which 
usually  requires  about  ninety  minutes.  The  distillate  Is  titrated  with 
fresh  standard  alkali. 

This  modification  of  the  usual  methods  avoids  the  danger  of  phos- 
phoric acid  being  carried  over  mechanically.  In  grinding  the  sample 
care  must  be  taken  not  to  lose  moisture.  It  is  recommended  to 
evaporate  the  titrated  distillate  and  apply  the  usual  qualitative  test 
for  phosphoric  acid  to  make  sure  that  no  appreciable  amount  of  this 
has  been  carried  over.  The  distillate,  of  course,  contains  all  the  other 
volatile  acids  present  of  which  the  salts  are  present  in  the  sample. 

The  phosphoric  acid  employed  for  the  distilla- 
tion must  be  free  from  nitric  acid,  which  if  present 
may  be  eliminated  by  adding  a  little  ammonia, 
and  heating  the  acid  to  fusion  in  platinum.  If 
either  the  phosphoric  acid  or  the  sample  itself 
contains  chlorides,  some  silver  sulphate  must  be 
added  to  the  contents  of  the  retort.  Oxalic  acid 
may  be  substituted  for  the  phosphoric  acid,  the 
solution  being  filtered  from  the  precipitated  cal- 
cium oxalate  before  introduction  into  the  retort. 
Hydrochloric  acid  may  be  used  instead,  provided 
that  the  amount  which  passes  into  the  distillate 
be  estimated  and  subtracted  from  the  total  acidity 
as  deduced  from  the  titration.  Sulphuric  acid  A 
should  not  be  used,  as  its  reaction  on  the  tarry 
matters  occasions  the  formation  of  sulphurous 
acid,  which  increases  the  acidity  of  the  distillate. 

Gladding  has  recently  (/.  Indust.  and  Eng. 
Chem.,  1909,  i,  250)  reported  the  latest  modifi- 
cation of  the  process  as  carried  out  in  his  labor- 
atory with  satisfaction.  The  apparatus  shown 
in  Fig.  86  is  used.  2  grm.  of  the  sample  and 
30  c.c.  of  water  are  introduced  into  A  (about  300  c.c.  capacity); 
10  c.c.  of  phosphoric  acid  (sp.  gr.  1.7)  are  added  and  the  liquid 
boiled  gently  for  about  90  minutes  while  the  volume  is  kept  at  50  c.c. 
The  distillate,  condensed  in  C,  is  received  in  B  which  contains  30  c.c. 
of  standard  alkali.  At  the  end  of  90  minutes'  distillation  the  contents 
of  B  are  titrated.  The  distillation  should  be  continued  until  the 
distillate  is  neutral.  Phenolphthalein  is  used  as  an  indicator.  A 


FIG.  86. 


510  ACID    DERIVATIVES    OF    ALCOHOLS. 

blank  experiment  should  be  made.  The  volume  of  liquid  in  A  is 
kept  at  50  c.c.  by  adding  water  drop  by  drop  through  the  tube  H. 
Gladding  refers  to  a  paper  by  Fresenius  and  Griinhut  (Zeit.  anal. 
Chem.,  1908,  597)  in  which  these  authors  disapprove  of  his  method, 
but  he  shows  that  they  did  not  subject  it  to  proper  comparison  and 
that  the  method  is  trustworthy. 

When  pure  calcium  acetate  is  assayed  by  either  of  the  foregoing 
methods  accurate  results  may  be  obtained,  but  when  commercial 
samples  are  examined  the  errors  may  sometimes  become  serious.  On 
the  whole,  the  method  of  distillation  with  phosphoric  acid  is  the  most 
accurate,  but,  unless  carefully  performed,  the  results  are  liable  to  be 
below  the  truth,  from  incomplete  volatilisation  of  the  acetic  acid,  while 
on  the  other  hand,  they  may  be  excessive  if  nitric  or  other  volatile  acid 
be  present  in  the  phosphoric  acid  used. T 

Magnesium  Acetate. — Basic  magnesium  acetate  has  been  recom- 
mended as  an  antiseptic. 

Aluminum  Acetate. — This  salt  is  employed  in  solution  by  calico- 
printers  under  the  name  of  " red-liquor."  It  is  usually  prepared  by 
precipitating  a  solution  of  alum  or  aluminum  sulphate  by  means  of 
calcium  or  lead  acetate,  and  filtering  or  syphoning  off  from  the  pre- 
cipitated calcium  or  lead  sulphate.  When  prepared  by  means  of  alum, 
the  product  necessarily  contains  potassium  sulphate  or  ammonium 
sulphate  (according  to  the  kind  of  alum  used),  and,  as  an  excess 
of  the  precipitant  should  be  avoided,  aluminum  sulphate  is  al- 
ways to  be  expected.  Owing  to  calcium  sulphate  being  somewhat 
soluble  in  water,  it  will  be  met  with  in  red-liquors  prepared  with 
calcium  acetate.  Such  red-liquor  is  inferior  to  that  prepared  by  lead 
acetate.  Good  red-liquor  contains  the  equivalent  of  from  3  to  5%  of 

rThe  following  results,  reported  by  Allen  from  the  same  sample  of  "  acetate  of  lime  "  by 
different  methods,  show  the  nature  and  direction  of  the  errors  to  which  the  various  pro- 
cesses are  liable : 

Acetic  Acid. 
Per  cent. 

By  distillation  with  phosphoric  acid  and  titration  of  distillate,  47-4 

By  distillation  with  phosphoric  acid  and  titration  of  distillate,  48.0 

By  distillation  with  sulphuric  acid  and  titration  of  distillate,  48.6 

By  distillation  with  oxalic  acid  and  titration  of  distillate,  48.3 

By  distillation  with  oxalic  acid  and  titration  of  distillate,  48.4 

By  Fresenius'  method,  53-4 

By  Fresenius'  method,  53  . 

By  ignition  and  weighing  the  calcium  carbonate,  53  , 

By  ignition  and  titration  of  residue,  S3  . 

By  ignition  and  titration  of  residue,  53  • 

By  ignition  and  titration  of  residue,  54  • 

By  boiling  with  sodium  carbonate,  and  titrating  filtrate,  56  . 

By  boiling  with  sodium  carbonate,  and  titrating  filtrate,  56 . 

By  boiling  with  sodium  carbonate,  and  titrating  filtrate,  57-6 

Improvements  in  the  manufacture  of  calcium  acetate  render  the  discrepancies  resulting 
from  the  employment  of  different  methods  of  assay  less  striking  than  formerly. 


VINEGAR.  511 

alumina,  and  twice  that  proportion  of  acetic  acid,  and  has  a  gravity 
of  1. 1 20,  but  it  is  sometimes  met  with  as  low  as  1.087.  Sodium  carbon- 
ate is  often  added  to  red-liquor  to  neutralise  excess  of  acid. 

Iron  Acetates. — Both  ferrous  and  ferric  acetates  are  employed  in 
the  arts.  A  crude  variety  of  iron  acetate  is  extensively  manufactured 
by  dissolving  iron  in  pyroligneous  acid. 

Pyrolignite  of  Iron,  Iron  Liquor  or  Black  Liquor.-  -For  use  by 
calico-printers,  a  liquid  consisting  chiefly  of  a  solution  of  ferrous  acetate, 
but  always  containing  more  or  less  ferric  acetate,  is  prepared  by  acting 
on  Scrap-iron  by  crude  pyroligneous  acid  of  1.035  to  1.040  sp.  gr.  A 
purified  acid  gives  less  satisfactory  results.  The  product,  which  is  a  deep 
black  liquid,  has  a  gravity  of  1.085  to  1.090,  and  is  concentrated  by  boil- 
ing till  it  is  about  1.120,  when  it  contains  about  10%  of  iron.  It  is  then 
ready  for  use,  and  is  known  as  "printers'  iron  liquor."  Much  iron 
liquor  is  now  made  as  high  as  1.140.  For  use  by  dyers,  the  liquid  is 
not  concentrated  by  evaporation,  but  the  gravity  is  raised  by  the  addi- 
tion of  ferrous  sulphate  (copperas),  by  which  a  more  suitable  product  is 
said  to  be  obtained  than  is  yielded  by  iron  acetate  alone.  As  a  5% 
solution  of  crystallised  ferrous  sulphate  has  a  gravity  of  1.026,  the  ad- 
dition of  1/2  pound  of  copperas  to  the  gallon  of  " black  liquor"  will 
raise  it  from  1.085  to  i.m.  As  much  as  124  grm.  of  ferrous  sulphate 
per  1000  c.c.  has  been  met  with  in  iron  liquor.  The  sulphate  may  also 
result  from  the  addition  of  sulphuric  acid  to  the  pyroligneous  acid 
employed  for  dissolving  the  scrap-iron.  Iron  sulphate  may  be  detected 
and  estimated  by  precipitating  the  diluted  black  liquor  with  barium 
chloride.  233  parts  of  the  precipitate  represent  278  parts  of  crys- 
tallised ferrous  sulphate.  Black  liquor  is  frequently  adulterated  with 
common  salt,  a  5%  solution  of  which  has  a  gravity  of  1.036.  It  may 
be  detected  and  estimated  by  adding  nitric  acid  and  precipitating 
the  diluted  liquor  with  silver  nitrate.  Iron  chlorides  may  also  be 
present  owing  to  the  addition  of  hydrochloric  to  the  pyroligneous 
acid.  Hence  the  chlorine  must  not  be  assumed  to  exist  as  common 
salt  without  further  examination.  This  is  best  effected  by  heating 
the  liquid  with  nitric  acid,  adding  barium  nitrate  to  separate  the  sul- 
phates, precipitating  the  iron  and  excess  of  barium  by  ammonium 
hydroxide  and  carbonate,  evaporating  the  nitrate  to  dryness,  and 
igniting  the  residue,  when  any  common  salt  will  remain.  Tannin  is 
stated  to  be  occasionally  added  to  iron  liquor. 

Ferrous  acetate  is  sometimes  made  by  decomposing  a  solution  of 


512  ACID    DERIVATIVES    OF    ALCOHOLS. 

ferrous  sulphate  by  calcium  acetate.  The  liquor  has  usually  a  gravity 
of  1. 1 1,  and  contains  calcium  sulphate. 

Ferric  acetate  is  sometimes  preferred  by  dyers  and  printers  to 
the  ferrous  salt.  It  is  occasionally  prepared  by  decomposing  iron-alum 
or  ferric  sulphate  by  lead  acetate.  The  product  must  be  free  from 
excess  of  the  lead  salt,  and,  for  some  purposes,  excess  of  ferric  sul- 
phate must  be  avoided. 

Tincture  of  ferric  acetate  may  be  prepared  by  mixing  alcoholic 
solutions  of  potassium  acetate  and  ferric  sulphate,  and  filtering  from 
the  precipitated  potassium  sulphate. 

Lead  Acetates. — These  include  neutral  acetate,  Pb  (C2H3O2)2, 
often  called  "  sugar  of  lead,"  and  several  basic-  or  oxyacetates,  all 
of  which  are  more  or  less  soluble  in  water,  the  solutions  possessing 
an  alkaline  reaction  and  giving  a  precipitate  of  lead  carbonate  by 
the  action  of  carbon  dioxide.  A  solution  of  neutral  lead  acetate  is 
but  little  affected  by  carbon  dioxide.  By  suspending  basic  acetate 
in  water  and  passing  carbon  dioxide  through  the  liquid  as  long  as  it 
has  an  alkaline  reaction,  the  lead  is  separated  as  an  insoluble  car- 
bonate, and  may  be  filtered  off,  washed,  ignited  in  porcelain  (apart 
from  the  filter)  till  bright  yellow  when  cold,  and  weighed  as  lead 
monoxide.  The  lead  remaining  in  permanent  solution  exists  as 
acetate,  and  may  be  ascertained  by  precipitation  as  sulphate  or 
chromate. 

A  better  and  simpler  method  for  detecting  basic  acetate  in  a  sample 
is  to  dissolve  it  in  recently-boiled  water,  filter,  and  then  add  to  the  clear 
solution  an  equal  measure  of  a  i%  solution  of  mercuric  chloride.  A 
white  precipitate  proves  the  presence  of  basic  acetate.  The  assay 
may  also  be  conducted  by  methods  given  on  page  509. 

Fresenius  recommends  the  following  indirect  method  for  the  assay 
of  pyrolignite  and  lead  acetate:  logrm.  of  the  sample  are  dissolved 
in  water  in  a  flask  holding  500  c.c.,  60  c.c.  of  normal  sulphuric  acid  are 
added,  and  the  water  up  to  the  mark.  An  extra  1.3  c.c.  of  water  is 
added  to  compensate  for  the  bulk  of  the  precipitated  lead  sulphate. 
The  flask  is  closed,  well  shaken,  and  the  liquid  allowed  to  settle, 
too  c.c.  of  the  clear  liquid  are  taken  out,  precipitated  with 
barium  chloride,  and  the  precipitate  collected,  washed,  ignited  and 
weighed.  Its  weight,  multiplied  by  0.4206,  is  subtracted  from  0.588 
grm.  (the  weight  of  acid  added  to  each  100  c.c.  of  the  liquid).  The 
remainder,  multiplied  by  113.7  gives  the  percentage  of  lead  monoxide 


VINEGAR.  513 

in  the  sample.  Another  100  c.c.  of  the  clear  liquid  are  drawn  off 
and  titrated  with  N/ 1  sodium  hydroxide,  using  litmus  as  an  indi- 
cator. Multiply  the  number  of  cubic  centimetres  of  alkali  used  by 
0.060,  subtract  from  this  the  previously  obtained  weight  of  barium 
sulphate  multiplied  by  0.515  (  =  the  free  sulphuric  acid  expressed  in 
terms  of  acetic  acid),  and  the  remainder,  multiplied  by  50,  will  be  the 
percentage  of  acetic  acid  in  the  sample. 

Basic  Lead  Acetate. — Solutions  of  basic  lead  acetate  have  been 
long  used  in  medicine  and  formulas  for  their  preparation  are  given  in 
pharmacopoeias.  A  solid  basic  acetate  and  a  solution  are  much  used 
as  clarifying  agents  in  saccharimetry.  For  the  method  of  preparing 
such  a  solution  see  page  308. 

Cupric  Acetates. — Several  of  these  salts  are  known  and  exten- 
sively used  in  the  arts.  They  are  prepared  by  the  action  of  acetic 
acid  on  copper  oxide  or  carbonate  or  upon  metallic  copper  with  access 
of  air.  The  neutral  acetate  is  freely  soluble  in  water,  but  several 
basic  acetates  exist.  They  are  of  different  shades  of  color,  and  are 
known  as  blue  and  green  verdigris. 

Verdigris  of  good  quality  is  dry,  soluble  in  dilute  acetic  acid,  sul- 
phuric acid  and  ammonium  hydroxide.  It  should  not  contain  more 
than  4%  of  impurities.  A  good  sample  will  correspond  to  about  the 
following  composition:  cupric  oxide,  43.5;  acetic  anhydride,  29.3; 
water,  25.2;  and  impurities,  2.0.  It  is  frequently  adulterated.  Sand, 
clay,  pumice  and  chalk;  barium,  calcium  and  copper  sulphates;  and 
iron  and  zinc  compounds,  are  sometimes  present.  Zinc  in  verdigris 
is  usually  due  to  the  use  of  sheets  of  brass  instead  of  copper  for  cor- 
rosion by  acetic  acid. 

On  dissolving  the  sample  in  dilute  hydrochloric  acid,  any  sand, 
clay,  pumice,  or  barium  sulphate  will  be  left  insoluble,  and  may  be 
collected  and  weighed.  (About  3%  of  insoluble  matter  is  allowable 
in  verdigris.  If  the  residue  amounts  to  6%  the  sample  is  inferior. 
Calcium  sulphate  in  large  proportion  may  be  left  partially  in  the  insol- 
uble residue).  If  the  sample  effervesced  on  addition  of  acid,  a  car- 
bonate is  present,  though  it  may  be  that  of  copper.  From  a  measured 
portion  of  the  solution  in  acid  the  sulphates  may  be  precipitated  by 
barium  chloride,  the  precipitate  collected  and  weighed. 

For  the  detection  of  the  metals,  the  sample  should  be  ignited,  the 
residue  dissolved  in  hydrochloric  acid,  and  the  copper  precipitated  from 
the  diluted  liquid  by  a  current  of  hydrogen  sulphide.  In  the  filtrate 
VOL.  1—33 


514  ACID    DERIVATIVES    OF   ALCOHOLS. 

the  excess  of  hydrogen  sulphide  is  destroyed  by  bromine  water,  the 
liquid  nearly  neutralised  by  ammonium  acetate,  and  then  boiled 
with  ammonium  acetate.  The  precipitate,  when  washed  and  ignited, 
is  ferric  oxide.  The  nitrate  from  the  iron  precipitate  is  treated  with 
hydrogen  sulphide  and  any  white  zinc  sulphide  filtered  off,  carefully 
roasted  and  weighed  as  oxide.  From  the  filtrate,  the  calcium  is  pre- 
cipitated by  ammonium  oxalate.  The  precipitate  yields  calcium 
carbonate  on  gentle  ignition,  the  weight  being  equal  to  the  chalk  in 
the  quantity  of  the  sample  taken.  The  calcium  may  be  determined 
more  readily,  but  less  accurately,  by  dissolving  the  sample  in  hydro- 
chloric acid,  precipitating  the  iron  by  bromine  and  ammonium 
hydroxide,  and  then  at  once  treating  the  filtrate  with  ammonium 
oxalate.  Of  course,  it  does  not  follow  that  all  the  calcium  found 
exists  as  chalk,  unless  sulphates  are  absent. 


HOMOLOGUES  OF  ACETIC  ACID.     Lower  Fatty  Acids. 

Acetic  acid  is  the  most  important  and  best  known  of  the  homolo- 
gous series  called  "the  fatty  acids."  These  acids  have  the  general 
formula  CnH2nO  2.  The  lower  members  of  the  series  are  volatile  liquids 
closely  resembling  acetic  acid.  The  higher  members  of  the  series 
are  insoluble  in  water,  not  volatile  without  decomposition,  and  solid 
at  ordinary  temperatures.  Many  fatty  acids  are  known,  but  the 
greater  number  are  of  very  limited  importance. 

The  higher  members  of  the  fatty  acid  series  are  almost  exclusively 
obtained  by  the  saponification  of  the  fixed  oils,  fats  and  waxes,  and 
such  of  them  as  require  description  will  be  considered  in  the  section 
treating  of  these  bodies.  The  present  article  is  limited  to  a  considera- 
tion of  the  lower  members  of  the  series,  sensibly  volatile  or  soluble 
in  water,  and  hence  liable  to  occur  under  the  same  circumstances  as 
acetic  acid. 

With  the  exception  of  the  first  three,  all  the  members  of  the  acetic 
series  of  acids  are  capable  of  isomeric  modification.  The  number  of 
such  modifications  increases  rapidly  with  the  number  of  carbon  atoms 
in  the  molecules,  and  many  have  been  obtained. 

The  following  table  gives  the  names  of  the  normal  and  isoacids  of  the 
acetic  series  up  to  the  member  with  7  carbon  atom.  Above  caproic 
acid  the  modifications  have  been  imperfectly  differentiated.  A 


HOMOLOGUES    OF   ACETIC   ACID. 


515 


table  of  the  still  higher  members  of  the  series  will  be  given  in  the  sec- 
tion on  "Saponification." 

From  this  table  it  will  be  observed  that  the  b.  p.  of  the  normal  fatty 
acids  show  a  tolerably  regular  increase  of  18°  to  22°  for  each  incre- 
ment of  CH2  in  the  formula.  The  isoacid  in  each  case  boils  at  a  lower 
temperature  than  the  normal  and  has  also  lower  sp.  gr.  The  sp.  gr. 
and  solubility  of  the  fatty  acids,  as  also  the  solubility  of  many  of  their 
salts,  decrease  with  an  increase  in  the  molecular  weight.  The  ethers 
of  the  fatty  acids  similarly  diminish  in  solubility  and  volatility  with 
each  increase  in  the  number  of  carbon  atoms. 


Empiri- 
cal                      Name 
Formula 

Constitutional  Formula 

Boil- 
ing 
Point 
0  C. 

Specific 
Gravity 
at  o°  C. 

Solubility 
in 
Water 

f  M  i  scible 

CH2O2         Formic  acid,    .    .    . 

H.COOH 

IOO 

j  in  all  pro- 

[  portions 

C2H4O2 

Acetic  acid  

CHs.COOH 

119 

Do 

C3H602 

Propionic  acid,   . 

CH3.CH2.COOH 

140 

1.016 

Do 

f  Normal  butyric  acid 
C4HgO2    -i  Iso-butyric  acid  ;  or  ) 
I    dimethaceticacid,  j 

CH3.(CH2)2.COOH 
CH(CH3)2.COOH 

163   . 
IS4 

.9817    .    .            Do 
.   .  .9596        Soluble 

Normal   pentoic  or  | 
valeric  acid,  .    .    .  / 

CH3.(CH2)3.COOH 

185    . 

9S  7  7             {Sparingly 
•     (    (x  in  30) 

C5HioO2 

Iso-pentoic     acid;  1 

ordinary     valeric  i 
acid  ;  or  iso-prop-  | 

CH(CH2)2.CH2.COOH 

•   175 

.   .  .9536          Do 

acetic  acid,   .    . 

CeHi2O2   {  Normal  caproic  acid  | 

CH3.(CH2)4.COOH 

205   . 

f  Nearly  in- 
•945°    •    •     i     soluble 

[  Iso-caproic  acid,    . 
f  Normal  oenanthylic  ) 
CiHuO*   \      acid  '.    .  ) 

CH(CH3)2.(CH2)2.COOH 
CH3.(CH2)5.COOH 

.    199 
224    . 

.   .   .931°           Do 
f  Almost 
•9345    •    •     |   insoluble 

1,  Iso-oenanthylic  acid 

CH(CH3)2.(CH2)3.COOH 

.    213 

Do 

As  a  rule,  the  isoacids  present  very  close  resemblances  to  the 
corresponding  normal  acids,  their  lower  gravities  and  b.  p.  and  greater 
susceptibility  to  oxidation  being  the  most  marked  distinctions.  In 
some  cases,  differences  are  observable  in  the  solubility  and  crystallisa- 
bility  of  the  salts. 

As  a  class,  the  lower  members  of  the  acetic  acid  series  may  be  sepa- 
rated from  most  other  organic  acids  (except  lactic  acid)  by  treating 
the  aqueous  solution  with  finely-ground  lead  monoxide  in  quantity 
sufficient  to  render  it  slightly  alkaline.  On  filtering,  the  lead  salts  of 
most  organic  acids  will  be  left  insoluble,  while  those  of  the  acetic  series 
will  be  found  in  the  filtrate. 

The  separation  of  the  lower  acids  of  the  acetic  series  from  each  other 
cannot  usually  be  effected  readily;  the  most  satisfactory  methods  are 
based  on  the  following  principles: 


ACID    DERIVATIVES    OF    ALCOHOLS. 

The  lowest  members  of  the  series  are  the  most  readily  soluble  in 
aqueous  liquids,  formic,  acetic,  propionic  and  normal  butyric  acid, 
being  soluble  in  all  proportions.  All  but  formic  and  acetic  acids  are 
separated  from  their  aqueous  solutions  by  saturating  the  liquid  with 
calcium  chloride,  when  they  rise  in  the  form  of  oils.  A  more  perfect 
separation  from  acetic  and  formic  acids  of  the  acids  higher  than 
valeric  may  be  effected  by  shaking  the  acidulated  aqueous  solution 
with  ether,  which  dissolves  the  higher  homologues  together  with 
more  or  less  of  the  lower.  On  agitating  the  ethereal  layer  with 
a  strong  solution  of  calcium  chloride  the  formic  and  acetic  acid 
pass  into  the  latter,  and  by  repeating  the  treatment  may  be  perfectly 
removed  from  the  ether,  with  little  or  no  loss  of  the  higher 
homologues. 

The  lower  members  of  the  series  are  most  active.  Hence,  if  an 
amount  of  alkali  insufficient  for  complete  neutralization  be  added  to  a 
solution  containing  the  free  acids,  and  the  liquid  be  then  distilled,  the 
higher  members  of  the  series  pass  over  in  the  free  state,  while  the  lower 
members  remain  behind  as  fixed  salts. 

If  sodium  hydroxide  is  added  to  a  mixture  of  butyric  and  valeric 
acids  in  quantity  insufficient  to  neutralise  the  whole,  and  the  liquid 
be  then  distilled,  the  distillate  will  consist  of  pure  valeric  acid  and 
the  residue  will  contain  mixed  sodium  butyrate  and  valerate;  or 
else  the  distillate  will  contain  the  whole  of  the  valeric  acid  and  some 
butyric  acid,  and  the  residue  will  consist  entirely  of  butyrate  of  sodium. 
In  either  case,  a  portion  of  one  of  the  acids  is  obtained  free  from  the 
other.  In  the  first  case,  the  residue  of  mixed  valerate  and  butyrate 
may  be  treated  with  sufficient  dilute  sulphuric  acid  to  neutralise  half 
of  the  sodium  hydroxide  originally  used,  and  the  mixture  redistilled, 
when  a  fresh  quantity  of  valeric  acid  will  be  obtained,  either  pure  or 
mixed  with  butyric  acid  according  to  the  relative  proportions  of  the 
two  acids  present  in  the  original  mixture.  In  the  latter  case,  by 
partially  neutralising  the  distillate  with  alkali,  and  again  distilling,  a 
further  separation  may  be  effected,  and  by  repeating  the  operation  in  a 
judicious  manner  two  or  even  more  of  these  volatile  fatty  acids  may  be 
separated  fairly  well  from  each  other. 

Although  the  foregoing  method  is  well  suited  to  the  separation  of 
normal  butyric  and  valeric  acids,  the  principle  is  wholly  at  fault  when 
iso-valeric  acid  is  in  question,  for  this  acid  completely  decomposes 
normal  butyrates. 


HOMOLOGUES    OF   ACETIC   ACID.  517 

An  approximate  separation  of  the  homologues  higher  than  valeric 
acid  can  be  effected  by  a  fractional  crystallisation  of  their  barium 
salts.  The  following  is  the  order  in  which  the  barium  salts  are 
deposited : 

From  aqueous  solutions.  From  alcoholic  solutions. 

T3  „,.;,,«,  T        Tior'inrr\    r»o  -r\ftrl  of** 


1.  Barium  caprate. 

2.  Barium  pelargonate. 

3.  Barium  caprylate. 

4.  Barium  oenanthylate. 

5.  Barium  caproate. 


1.  Barium  caprylate. 

2.  Barium  oenanthylate. 

3.  Barium  pelargonate  and  cap- 
rate. 

4.  Barium  caproate. 


The  aqueous  or  alcoholic  solution  of  the  acid  is  neutralised  with 
standard  aqueous  or  alcoholic  solution  of  sodium  hydroxide  (according 
as  the  crystallisation  is  to  be  effected  from  an  aqueous  or  alcoholic  solu- 
tion), an  amount  of  barium  chloride  equivalent  to  the  alkali  is  next 
added,  and  the  resultant  liquid  evaporated  and  allowed  to  deposit  crys- 
tals. The  crops  of  crystals  from  an  aqueous  solution  may  be  washed 
with  hot  alcohol,  the  washings  containing  the  salts  in  the  reverse  order 
of  their  deposition  from  alcoholic  solution. 

Another  method  of  detecting  and  estimating  acids  of  the  acetic  series 
when  in  admixture  with  each  other  is  based  on  the  different  compo- 
sition of  their  barium  salts,  the  process  being  as  follows:  The  free 
acids  obtained  by  distillation  are  saturated  by  barium  carbonate  or 
by  the  cautious  addition  of  baryta  water  (using  phenolphthalein  to 
indicate  the  point  of  neutrality),  the  latter  method  being  preferable 
for  the  higher  numbers  of  the  series.  In  this  way,  neutral  barium 
salts  are  formed,  which  may  be  obtained  in  the  anhydrous  state  by 
evaporating  off  the  water  and  drying  the  residue  at  130°.  These 
barium  salts  contain  percentages  of  barium  dependent  on  the  atomic 
weights  of  the  fatty  acids  present.  On  moistening  the  residue  with 
sulphuric  acid  and  then  igniting,  an  amount  of  barium  sulphate  is  ob- 
tained proportional  to  the  percentage  of  barium  contained  in  the 
salt  of  the  fatty  acid  present.  Instead  of  weighing  the  barium  sul- 
phate, a  standard  solution  of  baryta  water  may  be  employed  and  the 
weight  of  barium  (or  its  equivalent  of  barium  sulphate)  calculated  from 
the  volume  of  solution  employed.  This  method  also  serves  as  a  useful 
check  on  the  determination  of  the  weight  of  barium  sulphate.  The 
following  table  shows  the  proportions  of  barium  contained  in,  and  of 
barium  sulphate  producible  from  the  barium  salts  of  the  lower  acids 
of  the  acetic  series : 


ACID    DERIVATIVES    OF    ALCOHOLS. 


Name  of  salt 

Barium,  %. 

Barium  sulphate; 

Barium 

formate 

70  25 

no  47 

acetate  
propionate  :  .  . 
butyrate  
valerate 

53-73 
48.41 

44-05 

4O   4.1 

91-37 
82.13 

74-91 
68  73 

« 

caproate 

37    33 

63  48 

• 

oenanthylate 

34   68 

c8  08 

a 

caprylate.                                         .  . 

32.39 

55  °8 

a 

pelargonate  

30.38 

51.66 

a 

caprate  

28.60 

48.64 

From  this  table  it  will  be  seen  that  the  pure  barium  salts  of  the 
lower  acids  of  the  acetic  acid  can  very  readily  be  distinguished  from 
each  other  by  estimating  the  percentage  of  barium  contained  in  them. 
In  the  case  of  mixtures  of  two  acids  the  identity  of  which  is  established, 
the  proportions  in  which  the  two  are  present  may  be  calculated  from  the 
following  formula,  in  which  x  is  the  percentage  of  barium  salt  of  the 
lower  fatty  acid  in  the  mixed  barium  salts  obtained;  P,  the  percentage 
of  barium  sulphate  yielded  by  the  mixed  barium  salts  on  treatment 
with  sulphuric  acids;  B,  the  percentage  of  the  same  theoretically 
obtainable  from  the  pure  salt  of  the  lower  fatty  acid;  and  b,  the  per- 
centage of  the  same,  theoretically  obtainable  from  the  pure  salt  of  the 
higher  fatty  acid.  Then  — 


For  example,  suppose  a  mixed  barium  salt  known  or  assumed  to 
consist  of  acetate  and  valerate  to  have  yielded  a  precipitate  of  barium 
sulphate  equivalent  78.45%  of  the  weight  taken,  when  treated  with  sul- 
phuric acid  and  ignited.  Then,  by  the  above  formula, 

91.  37*=  7845  +  68.  73*  -6873 
therefore  22.64^  =  972 

and  #  =  42.93. 

Hence  the  mixed  barium  salt  .consisted  .of  42.93  of  barium  acetate, 
and  57.07  of  barium  valerate.  From  these  data  and  the  weight  of 
mixed  barium  salt  found,  the  actual  amounts  of  acetic  and  valeric  acid 
may  be  calculated. 

The  above  method  was  proposed  by  Dupre  for  approximately  deter- 
mining the  fusel  oil  in  spirits.  In  this  case  the  various  alcohols  are  first 
converted  into  the  corresponding  acids  by  oxidation  with  chromic-acid 
mixture. 


FORMIC   ACID. 


519 


It  has  been  stated  that  butyric  and  valeric  acids  are  extracted  from 
a  water  solution  by  shaking  with  benzene  while  formic  and  acetic  re- 
main in  the  water  (see  Analyst,  1908,  33,  133). 

Duclaux  (Ann.  Chim.  Phys.  [5]  1874,  2,  289)  claimed  to  have 
established  that  each  of  the  lower  acids  of  the  formic  series  has  its 
own  rate  of  distillation,  whether  alone  or  mixed  with  homologues. 
Several  investigators  have  gone  over  this  method  and  found  it  unsatis- 
factory. H.  D.  Richmond  (Analyst,  1895,  20,  193,  217)  examined  it 
very  carefully  and  decided  that  in  the  form  given  by  Duclaux  it  is 
untrustworthy. 

Richmond  gives  as  the  result  of  many  experiments  the  following 
formula  for  the  distillation  of  each  acid,  but  it  is  not  established  that 
the  formula  will  apply  to  any  mixture. 


loo—    = 


100s-— 


In  this  formula,  x,  is  the  percentage  of  liquid  distilled,  y  the  per- 
centage of  acid  distilled  and  a  and  K  are  factors  for  each  acid  ascertained 
by  experiment,  as  follows  (K  is  practically  negligible)  : 


Formic  (Duclaux)  

o  4 

OOO7Q 

Acetic  (Duclaux) 

o  667 

Piopionic  (Duclaux) 

i   in 

OOO72  3 

Butvric  (Duclaux) 

2 

(?) 

Butyric  (Wollnv). 

2 

Butvric  (Richmond) 

2 

Valeric  (Duclaux)  .  .  . 

? 

(?) 

Caproic  (Duclaux)     

4 

oo^soS 

Caprylic  (Duclaux)    

8  (?) 

(?) 

For  an  illustration  of  the  practical  application  of  this  method,  see  a 
paper  by  Richmond  in  Analyst,  1908,  33. 

Formic  Acid,  HCHO2. — Formic  acid  is  contained  in  the  liquid 
obtained  by  distilling  ants  with  water.  The  stings  of  some  insects 
and  plants  probably  contain  it.  It  is  usually  prepared  by  distilling 
oxalic  acid  with  glycerol.  A  formate  is  produced  in  the  decomposi- 
tion of  chloroform  or  chloral  by  an  alkali,  by  the  reaction  of  carbon 
monoxide  and  alkalies,  and  of  cyanogen  gas  or  cyanides  with  water. 

Formic  acid  is  a  colourless  volatile  liquid,  of  irritating  pungent  odour 


520  ACID    DERIVATIVES    OF    ALCOHOLS. 

and  very  sour.  It  has  a  sp.  gr.  of  1.2211  at  20°,  and  boils  at  100°. 
It  produces  intense  irritation  of  the  skin. 

In  general  properties  it  resembles  acetic  acid,  but  it  is  stronger  and 
more  readily  oxidised. 

The  formates  mostly  crystallise  well  and  are  all  soluble  in  water, 
Heated  with  concentrated  sulphuric  acid  they  do  not  blacken,  but  evolve 
pure  carbon  monoxide,  as  a  colourless  gas  burning  with  a  pale  blue 
flame.  A  neutral  solution  of  formate  gives  the  following  reactions: 

Silver  nitrate  gives,  in  concentrated  solutions,  white  crystalline  silver 
formate,  which  darkens  on  standing,  and  is  reduced  to  metallic  silver 
when  warmed.  If  the  liquid  be  too  dilute  to  allow  of  a  precipitate 
being  formed,  the  reduction  to  metallic  silver  still  occurs  on  heating,  a 
mirror  being  frequently  formed  on  the  sides  of  the  tube.  In  presence 
of  ammonium  hydroxide  the  reduction  is  retarded  or  prevented. 

Mercuric  chloride  is  reduced  on  heating,  with  production  of  white 
mercurous  chloride  or  grey  metallic  mercury,  according  to  the  propor- 
tion of  formate  present.  Acetates  do  not  give  this  reaction,  but  acetates 
and  chlorides  of  alkali  metals  retard  or  prevent  the  reduction.  The 
reduction  of  mercuric  formate  on  heating  may  be  applied  to  the  esti- 
mation of  formic  acid,  and  its  separation  from  acetic  acid  may  be 
approximately  effected  by  boiling  the  solution  of  the  free  acids  with 
yellow  mercuric  oxide  until  effervescence  ceases.  If  formic  acid  only 
is  present,  the  filtered  liquid  will  be  free  from  mercury.  With  a  mix- 
ture of  the  two  acids,  the  amount  of  mercury  which  passes  into  solution 
is  equivalent  to  the  acetic  acid  present.  If  the  total  acid  present 
originally  is  determined  by  standard  alkali  or  other  means,  the 
quantity  of  formic  acid  may  be  found,  or  in  presence  of  other  acids 
forming  soluble  mercuric  salts,  the  excess  of  mercuric  oxide  may 
be  dissolved  by  dilute  hydrochloric  acid,  and  the  residual  metallic 
mercury  weighed.  This  weight  multiplied  by  0.23  will  give  the  weight 
of  formic  acid  present. 

Chlorine,  bromine,  chromic  acid,  permanganates  and  other  power- 
ful oxidising  agents  convert  formic  acid  more  or  less  readily  into  car- 
bonic acid. 

When  heated  gently  with  alcohol  and  sulphuric  acid,  formates 
generate  ethyl  formate,  having  a  fragrant  odour  of  peach-kernels. 
With  ferric  chloride,  formates  react  similarly  to  acetates.  At  a  gentle 
heat,  strong  sulphuric  acid  evolves  carbon  monoxide  from  formic  acid 
or  a  formate.  Strong  alkalies  produce  an  oxalate. 


FORMIC   ACID.  521 

Lead  and  magnesium  formates  are  insoluble  in  alcohol,  while  the 
corresponding  acetates  are  soluble.  Hence,  acetic  may  be  separated 
from  formic  acid  by  saturating  the  free  acids  with  a  slight  excess  of  cal- 
cined magnesia  or  lead  carbonate,  filtering,  evaporating  the  nitrate  to 
a  small  bulk,  and  adding  a  large  proportion  of  alcohol.  Magnesium 
or  lead  formate  is  precipitated,  while  the  corresponding  acetate  re- 
mains in  solution.  The  process  may  be  modified  by  precipitating 
the  alcoholic  solution  of  the  acids  with  an  alcoholic  solution  of  lead 
acetate,  and  washing  the  resultant  precipitate  with  alcohol. 

Formic  acid  may  be  detected  by  reduction  to  formaldehyde.  Fen- 
ton  and  Sisson  (Proc.  Cambridge  Philos.  Society,  1907,  14,  385) 
find  that  this  is  best  accomplished  by  the  action  of  magnesium  in 
powder  or  ribbon.  A  few  minutes  suffice  to  produce  sufficient  for- 
maldehyde for  detection  by  the  standard  tests.  Of  course,  the  absence 
of  formaldehyde  must  be  first  established.  If  it  is  present,  it  may 
be  destroyed  by  pure  potassium  cyanide  as  described  on  page  91. 
The  formic  acid  can  be  separated  by  distilling  and  the  distillate 
tested. 

In  addition  to  the  methods  already  indicated,  formic  acid  may  be 
estimated  by  titration  with  standard  alkali  or  by  decomposition  in  a 
carbonic  acid  apparatus  by  sulphuric  acid  and  potassium  dichromate, 
the  amount  of  formic  acid  present  being  deduced  from  the  weight 
of  carbon  dioxide  evolved.  44  parts  of  carbon  dioxide  are  equivalent 
to  46  parts  of  formic  acid. 

Formic  acid  and  sodium  formate  are  used  as  food  preservatives. 
Woodman  and  Burrell  (Tech.  Quart.  1908,  21,  i),  have  devised  the 
following  method  for  detecting  these  substances  in  food. 

50  grm.  of  the  sample  are  mixed  with  20  c.c.  of  20%  phosphoric 
acid  solution,  and  distilled  by  means  of  open  steam,  the  mixture  be- 
ing gently  heated  to  avoid  much  condensation.  A  distillate  of  about 
200  c.c.  should  be  collected.  Almost  all  the  formic  acid  is  thus  ob- 
tained. The  distillate  is  mixed  with  2  c.c.  of  30%  acetic  acid  (free 
from  formic)  and  0.2  grm.  calcium  hydroxide  in  form  of  milk  of  lime. 
If  the  distillate  is  very  acid  more  of  the  hydroxide  may  be  needed. 
The  solution  is  evaporated  to  small  bulk  over  a  free  flame,  and  then, 
on  a  steam-bath,  to  dryness.  The  evaporation  should  be  carried  as 
far  as  possible  over  the  flame,  as  the  boiling  prevents  the  formation  of 
a  crust  of  calcium  carbonate.  The  dry  residue  is  put  into  a  test-tube 
provided  with  a  cork  and  delivery  tube.  The  lower  end  of  the  de- 


522  ACID    DERIVATIVES    OF   ALCOHOLS. 

livery  tube  should  dip  into  about  3  c.c.  of  water  in  a  tube  standing 
in  cold  water.  The  test-tube  containing  the  dry  residue  is  heated 
gradually  to  redness,  or,  at  least  until  vapors  are  no  longer  produced. 
Formic  acid  or  a  formate  present  in  the  original  material  will  give 
formaldehyde  in  the  final  distillate.  W.  and  B.  use  the  fuchsin  test 
(seep.  257).  As  a  slight  reaction  is  produced  by  the  products  of 
destructive  distillation  even  in  absence  of  formate,  they  use  a  color 
standard  prepared  by  mixing  8  c.c.  of  copper  chloride  solution 
(12  grm.  CuCl2,  2H2O  in  1000  c.c.)  and  12.5  c.c.  cobalt  chloride  solu- 
tion (24  grm.  CoCl2,  6H2O  and  100  c.c.  strong  hydrochloric  acid  in 
1000  c.c.)  and  diluting  this  mixture  to  100  c.c.  Many  food  products 
were  tested  by  W.  and  B.,  and  found  not  to  give  a  color  greater  than 
the  standard,  while  0.025  grm-  °f  formic  acid  in  50  grm.  of  material 
gave  a  colour  from  4  to  6  times  as  deep. 

Propionic  Acid,  HC3H5O2. — This  body,  is  of  little  commercial 
importance,  but  its  detection  and  separation  from  its  homologues  are 
occasionally  necessary. 

Propionic  acid  is  contained  in  crude  oil  of  amber,  in  sour  coconut 
milk  and  in  certain  wines,  especially  when  the  fermentation  has  been 
pushed  too  far.  It  is  also  produced  by  the  fermentation  of  glycerol 
and  lactic  acid,  and  by  many  synthetic  methods.  It  closely  resembles 
acetic  acid,  but  has  an  odour  recalling  at  once  those  of  acetic  and 
butyric  acids.  It  boils  at  140°  and  has  a  sp.  gr.  of  0.996  at  19°. 

The  propionates  closely  resemble  the  acetates;  they  are  all  soluble  in 
water. 

The  following  method  is  described  by  Linnemann  for  the  separa- 
tion of  propionic  acid  from  its  lower  homologues :  The  free  acids  are 
evaporated  to  dryness  with  excess  of  litharge.  The  residue  is  then 
treated  with  cold  water  and  the  liquid  filtered.  Basic  propionate  of 
lead  dissolves,  while  any  acrylate  remains  insoluble,  together  with 
most  of  the  acetate  and  formate.  The  solution  is  boiled  and  stirred 
quickly,  when  the  propionate  separates  suddenly  and  almost  completely 
as  a  crystalline  precipitate,  soluble  in  cold  water,  but  which  may  be 
filtered  at  a  boiling  heat  from  the  remaining  acetate  and  formate. 
The  propionic  acid  of  fermentation  is  said  not  to  exhibit  this  reaction. 

Butyric  Acid,  HC4H7O2. — Two  modifications  of  this  acid  are 
known. 

Normal  butyric  acid,  C3H7.COOH,  occurs  ready-formed  in  various 
natural  products,  and  is  frequently  produced  by  the  decomposition  of 


BUTYRIC   ACID.  523 

animal  and  vegetable  matter.  Butyric  esters  exist  in  butter  and  cod- 
liver  oil  and  it  can  be  produced  by  a  special  fermentation  of  sugar. 

Normal  butyric  acid  is  a  colourless  mobile  liquid,  having  a  smell 
at  once  resembling  acetic  acid  and  rancid  butter.  It  is  soluble 
in  water,  alcohol  and  ether  in  all  proportions,  but  is  not  soluble  in 
concentrated  solution  of  calcium  chloride  or  common  salt;  hence  it 
may  be  separated  from  its  aqueous  solution  by  saturating  the  liquid 
with  calcium  chloride  and  agitating  with  ether.  From  the  ethereal 
layer  it  may  be  recovered  by  spontaneous  evaporation  or,  as  a  salt, 
by  agitation  with  excess  of  solution  of  sodium  hydroxide. 

For  other  methods  of  approximately  separating  butyric  from  acetic 
and  valeric  acids  se'e  page  515. 

Isobutyric  acid,  CH(CH3)2.COOH,  occurs  in  carob  beans  and 
among  the  acids  derived  from  castor  oil.  It  closely  resembles  the  nor- 
mal acid  in  its  general  properties,  but  has  a  lower  b.  p.  and  sp.  gr. 
Its  smell  is  less  offensive  than  that  of  the  normal  acid  obtained  by  the 
decomposition  of  butter  or  by  fermentation  of  sugar.  It  requires 
3  parts  of  cold  water  for  solution,  and  is  easily  oxidised  to  acetic 
acid  and  carbon  dioxide  when  heated  with  chromic-acid  mixture 
(page  236). 

All  butyrates  are  soluble  in  water.  Lead  butyrate  is  a  heavy  liquid, 
which  solidifies  when  cooled. 

Copper  butyrate  forms  bluish-green  monoclinic  crystals,  which  are 
sparingly  soluble  in  water.  The  formation  of  this  salt  may  be  em- 
ployed to  distinguish  butyric  from  valeric  acid. 

The  isobutyrates  closely  resemble  the  butyrates,  except  those  con- 
taining calcium  and  silver.  Normal  calcium  butyrate  is  very  soluble 
in  cold  water,  but  separates  as  a  crystalline  precipitate  on  heating 
the  strong  solution  to  70°.  The  isobutyrate  is  more  soluble  in  hot 
water,  and  separates  on  cooling  as  a  crystalline  magma. 

Ethyl  butyrate  can  be  formed  by  heating  a  butyrate  with  alcohol 
and  strong  sulphuric  acid.  It  has  a  fragrant  odour  of  pineapple, 
and  boils  at  120°. 

Ethyl  butyrate  is  produced  when  butter-fat  is  saponified  by  alcoholic 
solution  of  a  strong  alkali.  The  reaction  is  easily  brought  about  by 
adding  a  small  piece  of  butter  (it  is  not  necessary  to  render  out  the  fat) 
to  some  strong  solution  of  sodium  hydroxide  in  alcohol,  and  heating 
the  mass  cautiously  until  it  foams  actively.  The  liquid  is  then  quickly 
poured  into  a  comparatively  large  volume  of  cold  water,  when  the 


524  ACID    DERIVATIVES    OF    ALCOHOLS. 

characteristic  odour  of  the  ester  is  easily  noticed.  The  equation  of  the 
reaction  is  unknown.  The  test  is  a  convenient  one  for  distinguishing 
butter  from  straight  butter  substitutes,  but  is,  of  course,  of  no  value 
for  mixtures  containing  appreciable  amounts  of  butter-fat. 

Valeric  Acid;  Valerianic  Acid;  H2C5H9O2. — Four  forms  of 
this  are  possible,  derived  from  the  four  primary  amyl  alcohols. 

Propyl-acetic  Acid;  Normal  Valeric  Acid. — This  is  obtained  by 
synthetic  methods,  also  from  calcium  lactate  by  the  action  of  some 
fission  fungi  and  by  the  action  of  an  enzyme  contained  in  the  tissues  of 
Ascarides  on  carbohydrates.  It  has  an  odour  recalling  that  of  butyric 
acid.  It  boils  at  185°  and  has  a  sp.  gr.  of  0.9415  at  20°. 

Methylethyl-acetic  Acid. — This  can  be  obtained  from  the  oil 
of  the  fruit  of  the  Angelica  archangelica  L.,  and  probably  exists  in  small 
amount  in  valerian  root.  It  is  optically  active,  having  the  value  [a]D 
=  17.85°.  Some  synthetic  forms  are  inactive  by  racemism,  but  the 
ordinary  form  of  active  amyl  aclohol  gives  the  dextrorotatory  form  of 
the  acid.  It  boils  at  about  172°. 

Isopropylacetic  Acid;  Isovaleric. — This  is  the  common  form, 
ordinarily  called  valerianic  acid.  It  occurs  in  valerian  root.  It  is 
optically  inactive,  but  when  prepared  from  valerian  root  often  has  slight 
optical  activity,  due,  it  is  thought,  to  a  small  amount  of  the  active  isomer. 
Esters  of  this  occur  in  dolphin  and  porpoise  oils,  in  sweat,  and  in  various 
other  products  and  secretions  of  animals.  It  exists  in  valerian  root  and 
many  Composite.  It  is  a  colourless,  oily  liquid,  with  an  odour  resem- 
bling old  cheese.  Its  taste  is  sharp  and  acid,  and  it  blanches  the  tongue. 
It  dissolves  in  about  30  parts  of  cold  water,  and  is  readily  soluble  in  al- 
cohol, ether,  chloroform  or  strong  acetic  acid.  It  is  almost  wholly 
removed  from  its  aqueous  solution  by  saturating  the  liquid  with  com- 
mon salt  or  calcium  chloride. 

This  acid  has  a  sp.  gr.  of  0.937  at  15°,  and  boils  as  175°.  It  forms 
a  hydrate  of  the  composition  C5H10O2,H3O,  having  a  density  of  0.950 
and  boiling  at  165°,  but  it  is  gradually  dehydrated  by  distillation,  the 
weaker  acid  coming  off  first.  On  the  other  hand,  on  distilling  the  dilute 
aqueous  acid,  the  first  portions  of  the  distillate  are  most  strongly  acid. 

Trimethylacetic  acid  is  solid  at  ordinary  temperatures,  melting 
at  35.4°  to  a  liquid  of  0.905  sp.  gr.  at  50°,  and  boiling  at  163.8°.  It 
is  optically  inactive. 

Reactions  of  Isovaleric  Acid  and  Isovalerates. — When  iso- 
valeric  acid  or  an  isovalerate  is  distilled  with  sulphuric  acid  and  a  little 


VALERIC   ACID.  525 

amylic  alcohol,  a  fragrant  ethereal  liquid  smelling  of  apples  is  ob- 
tained; this  is  amyl  isovalerate. 

Isovalerates  are  decomposed  by  acetic  acid  with  formation  of  iso- 
valeric  acid  and  an  acetate;  they  are  also  decomposed  by  tartaric, 
citric  and  malic  acids. 

Isovalerates  are  mostly  soluble  in  water.  Iron  and  bismuth  oxy- 
isovalerates  are  insoluble.  Silver  and  mercurous  isovalerates  are 
but  slightly  soluble,  and  aluminum  isovalerate  is  insoluble.  Neither 
this  acid  nor  butyric  gives  a  precipitate  with  an  aqueous  solution 
of  zinc  acetate.  This  fact  distinguishes  them  from  caproic  acid, 
which  throws  down  sparingly  soluble  zinc  caproate  as  a  white 
crystalline  precipitate. 

Barium  isovalerate  crystallises  easily  in  triclinic  scales  or  tables 
(in  distinction  from  the  same  compound  from  active  valeric  acid),  is 
soluble  in  2  parts  of  cold  water  and  sparingly  soluble  in  alcohol. 
Barium  caprylate  requires  120  parts  of  cold  water  for  solution,  and  is 
nearly  insoluble  in  alcohol.  Barium  caprate  is  almost  insoluble  in 
water. 

When  concentrated  isovaleric  acid  is  agitated  with  solution  of  cop- 
per acetate,  anhydrous  copper  isovalerate  separates  in  oily  drops  which, 
in  from  5  to  20  minutes,  crystallise  as  greenish-blue  monoclinic  prisms 
or  octohedra  of  hydrated  copper  isovalerate,  moderately  soluble  in 
water  and  alcohol.  The  salt  is  less  soluble  in  hot  water  than  in  cold, 
and  hence  the  saturated  solution  becomes  turbid  when  heated.  This 
reaction  distinguishes  the  acid  from  butyric  acid,  which  forms  with  a 
moderately  strong  solution  of  copper  acetate  an  immediate  precipitate 
or  turbidity  of  copper  butyrate,  of  bluish-green  colour,  and  crystallising 
in  small  monoclinic  prisms.  In  using  this  test  for  assay  the  acid 
must  first  be  obtained  free  by  distilling  the  salt  with  a  moderate 
excess  of  sulphuric  acid. 

Isovaleric  acid  may  be  separated  from  most  organic  acids  by  convert- 
ing it  into  the  soluble  lead  salt.  Acetic  acid  may  be  detected  by  neu- 
trallising  any  free  acid  with  sodium  hydroxide,  and  precipitating  in  the 
cold  with  excess  of  ferric  chloride.  In  presence  of  acetic  or  formic  acid, 
the  filtered  liquid  will  have  a  red  colour.  The  insolubility  of  aluminum 
isovalerate  might  probably  be  employed  for  the  separation  of  the  acid 
from  acetic  or  formic  acid. 

For  other  methods  of  estimating  the  acid  and  separating  it  from  its 
homologues,  see  page  515. 


526  ACID    DERIVATIVES    OF    ALCOHOLS. 

Commercial  Valeric  Acid  and  Valerates. — The  presence  of  alco- 
hol, acetic  acid,  butyric  acid  and  valerates,  in  commercial  valeric  acid  is 
indicated  by  the  increased  solubility  of  the  sample,  which  should  not  be 
greater  than  i  of  the  hydrated  acid  in  26  parts  by  weight  of  water.  If 
the  sample  requires  more  than  30  parts  of  cold  water  for  solution,  the 
presence  of  higher  homologues,  or  valeral  (valeraldehyde,  C5H10O) 
is  indicated.  Acetic  acid  may  be  recognised  as  indicated  on  page  525. 
By  neutralising  the  sample  with  an  alkali,  any  amyl  alcohol,  valeric 
aldehyde  or  neutral  ester  will  be  left  undissolved,  as  a  turbidity  or 
oily  layer,  and  the  amount  may  be  estimated  by  measurement,  or  the 
mixture  may  be  shaken  with  ether,  and  the  ethereal  liquid  evaporated 
spontaneously.  The  solubility  of  valeric  acid  in  a  mixture  of  equal 
volumes  of  glacial  acetic  acid  and  water  may  be  employed  to  separate 
it  from  valeral  and  esters,  but  not  from  amyl  alcohol.  The  presence  of 
butyric  acid  will  be  indicated  by  fractional  distillation  and  by  the  com- 
position of  the  salt  obtained  by  saturating  the  acid  with  barium  car- 
bonate; also  by  the  reaction  with  copper  acetate. 

Valeric  acid  should  also  be  tested  for  non-volatile  impurities,  sul- 
phuric acid,  and  hydrochloric  acid. 

Valerates  have  been  somewhat  extensively  used  in  medicine,  espe- 
cially the  sodium,  iron,  zinc  and  bismuth  salts.  They  are  all  more 
or  less  liable  to  adulteration,  which  in  some  instances  is  very  gross. 
Thus,  samples  of  zinc  valerate  are  occasionally  composed  of  the  sul- 
phate or  acetate,  and  others  have  been  met  with  which  consisted  of 
zinc  butyrate  impregnated  with  oil  of  valerian.  Zinc  valerate  is  also 
liable  to  adulteration  with  tartaric  and  citric  acids,  boric  acid  and  other 
substances.  Similarly,  iron  tartrate  or  citrate  flavoured  with  valerian 
has  been  substituted  for  the  iron  valerate,  and  the  quinine  sulphate 
for  the  valerate.  Ammonium  valerate  has  been  prepared  by  saturat- 
ing calcium  chloride  with  oil  of  valerian,  and  many  similar  frauds  have 
been  practised. 

Most  of  the  above  adulterations  may  be  readily  detected.  The  sub- 
stitution of  zinc  butyrate  for  valerate  is  best  recognised  by  distilling 
the  salt  with  sulphuric  acid  diluted  with  an  equal  measure  of  water, 
and  then  applying  the  copper  acetate  and  other  tests  to  the  distillate. 

The  most  satisfactory  ready  test  for  valerates  is  to  weigh  or  measure 
the  layer  of  free  acid  which  separates  on  decomposing  the  solid  salt 
with  sulphuric  acid  diluted  with  an  equal  measure  of  a  saturated 
aqueous  solution  of  zinc  sulphate. 


OXALIC   ACID.  527 

Oxalic  Acid. 

This  acid  is  extensively  formed  in  the  physiologic  processes  of 
plants  and  animals.  It  is  usually  converted  into  calcium  oxalate, 
appearing  as  crystalline  deposits  (raphides)  in  cells  of  plants,  but 
potassium  hydrogen  oxalate  is  sometimes  found  in  plant  juices. 
Calcium  oxalate  is  often  found  in  small  amount  in  urine. 

Oxalic  acid  is  a  product  of  the  action  of  nitric  acid,  alkaline  potas- 
sium permanganate  and  other  oxidising  agents  on  many  organic  bodies. 

On  a  large  scale,  the  acid  is  usually  made  by  the  action  of  alkalies 
starch,  sawdust,  straw,  bran  or  similar  vegetable  matter  is  heated  with 
potassium  hydroxide  an  oxalate  is  formed.  Wheat  bran  yields  150% 
of  its  weight  of  crystallised  oxalic  acid.  Sodium  hydroxide  cannot  be 
advantageously  substituted,  but  with  a  mixture  of  the  alkalies  very 
satisfactory  results  are  obtained.  The  product  of  the  action  is  treated 
with  water,  and  the  solution  treated  with  slaked  lime.  The  alkalies 
are  thus  recovered.  The  calcium  oxalate  is  separated  and  decom- 
posed with  sulphuric  acid,  the  resulting  acid  being  separated  by 
evaporation  and  crystallisation. 

Oxalic  acid  usually  occurs  crystallised  with  2  molecules  of  water, 
in  monoclinic  prisms  having  a  sp.  gr.  of  1.641  at  4°.  Exposed  to 
dry  air,  or  in  vacuo  over  oil  of  vitriol,  the  crystals  lose  water,  become 
opaque,  and  form  a  white  powder.  The  acid  may  be  also  obtained 
anhydrous  by  exposure  to  a  gentle  heat  (60°  to  70°).  If  at  once 
heated  to  100°  the  crystals  melt,  and  it  is  then  much  more  difficult  to 
drive  off  the  water.  By  dissolving  ordinary  oxalic  acid  in  12  parts 
of  warm  concentrated  sulphuric  acid,  and  allowing  the  solution  to 
stand  for  several  days,  the  anhydrous  acid,  is  deposited  in  transpa- 
rent crystals,  which  on  exposure  to  air  absorb  water  and  fall  to 
powder. 

Saturated  solutions  of  oxalic  acid  lose  acid  at  100°,  and  the 
anhydrous  acid,  may  be  readily  sublimed.  This  furnishes  a  convenient 
mode  of  obtaining  the  pure  acid  for  analytic  purposes.  The  acid 
should  previously  be  rendered  anhydrous  by  heating  to  60°  or  70°, 
and  the  temperature  of  the  retort  must  be  kept  as  constantly  as  possible 
at  157°.  If  allowed  to  rise  to  160°,  much  loss  of  acid  occurs,  and  an 
inferior  product  is  obtained  containing  water  and  formic  acid.  The 
passage  of  a  current  of  dry  air  greatly  facilitates  the  sublimation. 

Oxalic  acid  is  colourless  and  odourless,  and  completely  volatile  by 
heat  without  charring. 


528  ACID    DERIVATIVES    OF   ALCOHOLS. 

ioo  parts  of  water  dissolve  8  parts  of  crystallised  oxalic  aeid  at  10° 
and  345  parts  at  90°.  The  solution  is  intensely  sour,  reddens  litmus 
strongly,  and  is  very  poisonous.  It  decomposes  carbonates,  phos- 
phates, chromates  and  many  other  salts,  including  fluorspar.  Pow- 
dered oxalic  acid  completely  decomposes  sodium  or  calcium  chloride 
when  the  mixture  is  heated.  Prussian  blue  dissolves  in  oxalic  acid 
to  a  clear  blue  liquid,  sometimes  employed  as  a  blue  ink.  Solutions 
of  oxalic  acid  are  permanent  in  the  dark,  but  when  exposed  to  light 
the  acid  is  rapidly  decomposed. 

Crystallised  oxalic  acid  dissolves  readily  in  cold  and  still  more  readily 
in  boiling  alcohol.  It  is  but  slightly  soluble  in  ether,  and  is  insoluble 
in  chloroform,  benzene  or  petroleum  spirit. 

Oxalic  acid  is  not  affected  by  boiling  with  moderately  strong  nitric 
or  hydrochloric  acid.  Cold  sulphuric  acid  has  no  action  on  it;  but 
when  heated  with  concentrated  sulphuric  acid,  it  decomposes  into 
carbon  monoxide,  carbon  dioxide  and  water. 

When  heated  with  glycerol,  oxalic  acid  yields  carbon  dioxide  and 
water  at  a  moderate  heat  and  formic  acid  at  a  higher  temperature. 
This  is  the  method  commonly  employed  for  producing  formic  acid. 

Manganese  and  lead  dioxides  convert  oxalic  acid  in  carbon  dioxide 
and  water.  Auric  chloride  and  acid  solutions  of  permanganates  react 
similarly. 

Reactions  of  Oxalic  Acid  and  Oxalates. — An  aqueous  solution  of 
oxalic  acid  presents  the  following  analytical  characters : 

On  addition  of  lime-water  or  solution  of  calcium  acetate,  a  white 
precipitate  of  calcium  oxalate  is  formed.  The  precipitate  is  insoluble 
in  water,  and  not  sensibly  soluble  in  acetic  or  other  organic  acids. 
It  is  readily  soluble  in  dilute  mineral  acids.  It  is  decomposed  by  boiling 
with  excess  of  sodium  carbonate  solution,  with  formation  of  insoluble 
calcium  carbonate  and  soluble  sodium  oxalate.  On  gentle  ignition, 
calcium  oxalate  evolves  carbon  monoxide  and  leaves  calcium  carbon- 
ate. No  blackening  occurs.  Solutions  of  soluble  oxalates  give  the 
same  reaction  as  oxalic  acid  with  lime-water  or  calcium  acetate,  and 
react  with  calcium  sulphate  or  chloride  in  addition.  If  previously 
neutralised  by  ammonium  hydroxide,  oxalic  acid  solutions  are  precipi- 
tated by  the  two  latter  reagents. 

With  solutions  of  barium,  oxalic  acid  and  oxalates  react  in  a  similar 
manner  as  with  solutions  of  calcium,  but  the  resultant  barium  oxalate 
is  not  so  insoluble  in  water  or  acetic  acid  as  the  calcium  salt. 


OXALIC    ACID.  529 

On  addition  of  dilute  sulphuric  acid  and  manganese  dioxide,  warm 
solutions  of  oxalic  acid  and  oxalates  produce  effervescence,  owing  to  the 
formation  of  carbon  dioxide.  The  gas  may  be  proved  to  be  carbon 
dioxide  by  its  reaction  with  lime-water. 

In  presence  of  dilute  sulphuric  acid,  a  warm  solution  of  oxalic  acid 
rapidly  decolourises  potassium  permanganate.  From  strong  solutions, 
the  resultant  carbon  dioxide  escapes  with  effervescence. 

Estimation  of  Oxalic  Acid. — Oxalic  acid  may  be  estimated 
with  considerable  accuracy  by  either  of  the  following  methods, 
the  details  of  which  may  be  found  in  most  works  on  quantitative 
analysis: 

a.  By  precipitation  as  calcium  oxalate.  The  solution  should  be  hot 
and  dilute,  and  mineral  acids  must  be  absent  or  previously  neutralised 
by  ammonium  hydroxide.  In  the  absence  of  other  acids  forming 
insoluble  or  nearly  insoluble  calcium  salts  (e.  g.,  sulphates,  tartrates, 
citrates,  phosphates),  the  solution  may  be  exactly  neutralised  by  am- 
monium hydroxide,  and  calcium  chloride  added.  Any  phosphate  may 
be  separated  by  digesting  the  precipitate  with  cold  dilute  acetic  acid. 
In  presence  of  sulphates,  calcium  sulphate  should  be  employed  as  a 
precipitant.  It  is  frequently  preferable  to  have  the  solution  acid  with 
acetic  acid  or  to  precipitate  the  acid  solution  with  calcium  acetate,  so 
as  to  avoid  the  precipitation  of  other  calcium  salts.  Almost  all 
calcium  salts  are  soluble  in  acetic  acid,  except  the  oxalate,  racemate, 
and  fluoride.  Racemates  may  be  previously  removed  by  precipitation 
with  potassium  acetate  in  presence  of  alcohol.  The  separation  of 
oxalates  and  fluorides  is  rarely  required  in  practice,  but,  if  required 
the  oxalate  can  be  determined  by  titrating  the  precipitate  with  standard 
potassium  permanganate.  The  precipitate  of  calcium  oxalate,  how- 
ever produced,  is  to  be  well  washed  and  then  treated  in  one  of  the  follow- 
ing ways: 

1.  It  is  dried  at  1 00°,  and  weighed  as  calcium  oxalate. 

2.  .It  is  ignited,  moistened  with  ammonium  carbonate,  again  gently 
ignited,  and  weighed  as  calcium  carbonate. 

3.  It  is  moistened  on  the  filter  with  strong  sulphuric  acid,  and  the 
whole  ignited   again,  moistened   with   sulphuric  acid,    reignited,  and 
finally  weighed  as  calcium  sulphate. 

4.  It  is  ignited   thoroughly,  and   the  resultant  calcium  oxide   and 
carbonate  titrated  with  standard  acid. 

5.  The  filter  is  placed  in  a  beaker  together  with  water  and  dilute 

VOL.  1—34 


530  ACID    DERIVATIVES    OF   ALCOHOLS. 

sulphuric  acid,  and  the  liquid  is  titrated  with  standard  potassium 
permanganate. 

Of  these  methods,  the  last  two  are  perhaps  the  best,  because  they  are 
the  least  affected  by  impurity  in  the  precipitate.  Process  5  aims  at  the 
direct  estimation  of  the  oxalate,  and  may  be  applied  to  a  precipitate 
containing  phosphate,  carbonate,  or  sulphate;  but  tartrate,  racemate, 
and  most  organic  salts  must  be  absent  from  the  precipitate. 

b.  By  treatment  with  dilute  sulphuric  acid  and  manganese  dioxide  in 
a  carbon  dioxide  apparatus.     This  process  is  conducted  precisely  as 
in  the  valuation  of  a  manganese  ore,  except  that  excess  of  manganese 
dioxide  is  used  instead  of  excess  of  the  oxalate.     44  parts  by  weight 
of  carbon  dioxide  lost  by  the  apparatus  represent  63  of  crystallised,  or 
45  of  anhydrous  oxalic  acid. 

c.  By  titration  with  standard  permanganate.    The  solution  of  the  oxa- 
late must  be  free  from  other  readily  oxidisable  bodies,  and  should 
be  warm,  dilute,  and  pretty  strongly  acidulated  with  sulphuric  acid. 
The  permanganate  is  added  gradually,  with  constant  stirring,  until  the 
liquid  acquires  a  permanent  pink  tint.     The  permanganate  is  prefer- 
ably  standardised    with    pure    oxalic    acid.      N/io   potassium  per- 
manganate, is  a  suitable  strength.      Each  c.c.  of  this  solution  will 
oxidise  0.0063  grm-  of  crystallised  or  0.0045  grm-  °f  anhydrous  oxalic 
acid.     The  process  can  be  employed  for  titrating   a  precipitate  of 
calcium  oxalate.     . 

.  In  cases  of  poisoning  by  free  oxalic  acid,  the  acid  extracted  from  the 
stomach  and  intestines  is  chiefly  uncombined,  but  that  obtained  from 
the  liver,  kidneys,  heart  and  urine  is  in  combination. 

Commercial  oxalic  acid  is  not  much  liable  to  intentional  adulter- 
ation. 

Organic  matters  other  than  oxalic  acid  are  recognised  by  the 
charring  or  darkening  of  the  sample  when  heated,  or  on  warming  with 
concentrated  sulphuric  acid. 

Fixed  mineral  impurities  are  left  as  a  residue  on  igniting  the  sample 
in  the  air.  If  the  ignited  residue  effervesces  on  addition  of  dilute 
acid,  an  acid  oxalate  is  probably  present  in  the  sample.  Sensible 
quantities  of  lead  and  other  heavy  metals  are  sometimes  met  with. 
Sulphuric  acid  and  acid  sulphates  are  sometimes  present  in  considerable 
amount.  The  solution  of  such  samples  gives  a  white  precipitate  with 
barium  chloride.  The  same  impurities  occur  in  commercial  am- 
monium oxalate. 


SUCCINIC  ACID.  531 

Oxalates. — These  salts  require  but  little  special  description.  The 
metals  of  the  potassium  group  form  3  classes  of  oxalates,  the 
potassium  salts  having  the  formulas  K2C2O4,H2O;KHC2O4,H2O;  and 
KH3(C2O4)2,2H2O.  The  acid  salts  are  the  least  soluble.  The  oxalates 
from  most  other  metals  are  insoluble,  or  nearly  insoluble,  in  water. 
This  is  true  of  the  oxalates  from  barium,  strontium,  calcium,  copper, 
magnesium,  manganese,  cobalt,  nickel,  zinc,  lead  and  silver.  The  first 
4  of  these  retain  i  molecule  of  water  on  drying  at  100°.  The  re- 
mainder retain  2  molecules,  with  the  exception  of  the  lead  and  silver 
salts,  which  are  anhydrous.  Ferrous  oxalate  is  but  sparingly  soluble, 
but  ferric  oxalate  is  readily  so,  at  least  in  presence  of  free  oxalic  acid; 
hence  the  use  of  oxalic  acid  for  removing  ink-stains  and  dissolving 
Prussian  blue.  All  the  insoluble  oxalates  are  soluble  in  dilute  nitric 
acid,  but  they  are  generally  insoluble  in  acetic  acid.  The  estimation 
of  the  oxalic  acid  may  be  readily  effected  by  the  methods  described 
on  page  529. 

On  ignition,  oxalates  containing  metals  not  easily  reducible  evolve 
carbon  monoxide,  and  leave  carbonates.  These  may  sometimes  be 
further  decomposed  if  the  temperature  be  excessive.  Oxalates  con- 
taining more  easily  reducible  metals,  when  heated  to  redness  in  a  close 
vessel,  usually  leave  the  metal  and  evolve  carbon  dioxide.  This  re- 
action occurs  even  at  100°,  in  the  case  of  gold;  hence  gold  is  reduced  from 
its  solutions  by  boiling  with  an  oxalate. 

Pure  oxalates  do  not  char  on  ignition. 

Succinic  Acid. — Succinic  acid  occurs  naturally  in  amber  and  in 
certain  lignites;  is  produced  during  the  alcoholic  fermentation  of  sugar; 
and  by  the  fermentation  of  malic  acid  and  many  other  substances, 
especially  under  the  influence  of  putrefying  casein;  also  by  the  action 
of  nitric  acid  on  the  fatty  acids  and  fats,  and  it  exists  ready  formed  in 
several  plants. 

It  may  be  obtained  by  the  dry  distillation  of  amber,  the  watery  dis- 
tillate being  filtered  while  hot  to  separate  oil,  when  crystals  of  the 
acid  are  deposited  on  cooling,  and  may  be  purified  by  boiling  with 
nitric  acid,  followed  by  recrystallisation  from  water. 

Succinic  acid  bears  the  same  relation  to  butylene  (tetrene)  alcohol 
that  oxalic  acid  does  to  ethylene  glycol,  and  may  be  produced  from 
butylene  alcohol  by  oxidation.  It  may  also  be  obtained  by  the  deox- 
idation  of  tartaric  or  malic  acid,  which  contain,  respectively,  2  and  i 
atom  more  of  oxygen  than  does  succinic  acid. 


532  ACID    DERIVATIVES    OF    ALCOHOLS. 

Succinic  acid  crystallises  in  colourless,  oblique  rhombic  prisms  or 
plates.  When  heated  to  130°,  it  emits  suffocating  fumes,  and  ati8o° 
melts.  When  the  heat  is  increased  to  235°  the  acid  boils  and  sublimes 
as  succinic  anhydride,  which  melts  at  120°.  WThen  heated  strongly 
in  the  air,  succinic  acid  burns  with  a  blue  smokeless  flame. 

Succinic  acid  is  soluble  in  about' 18  parts  of  cold  and  0.8  boiling  water. 
It  dissolves  readily  in  alcohol  and  sparingly  in  ether,  but  is  insoluble 
in  chloroform,  benzene,  petroleum  spirit,  turpentine  or  carbon  disul- 
phide.  Nitric  acid,  chlorine  and  chromic  acid  have  no  action  on 
succinic  acid,  and  it  is  soluble  without  change  in  strong  sulphuric 
acid.  Permanganates  have  no  action  on  a  cold  acid  solution,  but  when 
heated  in  presence  of  free  alkali  produce  oxalic  acid. 

Reactions  of  Succinic  Acid. — In  its  analytical  characters  succinic 
acid  somewhat  resembles  benzoic  acid,  but  differs  from  it  in  not 
being  precipitated  from  a  strong  solution  of  its  salts  by  hydrochloric 
acid;  in  being  precipitated  by  ammoniacal  solution  of  barium  chloride 
even  from  a  dilute  solution ;  and  by  being  insoluble  in  chloroform,  and 
therefore  not  removable  from  an  acid  solution  by  agitation  with  that 
liquid.  Magnesium  benzoate  is  soluble  in  alcohol,  but  the  succinate 
is  insoluble. 

Ferric  chloride,  if  first  treated  with  as  much  ammonium  hydroxide 
as  it  will  bear  without  precipitation,  will  throw  down  from  neutral 
solutions  of  soluble  succinates  a  bulky  cinnamon-brown  basic  ferric 
succinate,  some  free  succinic  acid  being  simultaneously  produced,  and 
the  solution  acquiring  an  acid  reaction.  Benzoates,  under  similar  cir- 
cumstances, give  a  flesh-coloured  precipitate,  and  cinnamates  a  yellow. 
The  precipitate  may  be  filtered  off,  washed  and  decomposed  by  boiling 
with  excess  of  dilute  ammonium  hydroxide.  The  filtered  liquid,  if 
mixed  with  barium  chloride  and  an  equal  bulk  of  alcohol,  gives  a  white 
precipitate  of  barium  succinate.  By  the  above  combination  of  reac- 
tions, succinic  acid  may  be  readily  identified  and  separated  from  other 
organic  acids.  The  process  might  possibly  be  made  quantitative. 
For  such  a  purpose,  sodium  acetate  should  be  added  to  the  liquid  con- 
taining the  iron  precipitate,  and  the  whole  boiled,  the  precipitate  pro-' 
duced  being  first  boiled  and  then  washed  with  dilute  ammonium  hy- 
droxide, the  liquid  being  then  concentrated  and  precipitated  by  alcohol 
and  barium  chloride.  Neutral  succinates  containing  alkali  metals 
may  also  be  precipitated  pretty  completely  by  adding  barium  chloride 
to  the  boiling  solution. 


MALIC   ACID.  533 

Commercial  succinic  acid  has  usually  more  or  less  of  a  brown 
colour,  and  somewhat  of  the  odour  of  empyreumatic  oil  of  amber, 
which  impurity  may  be  removed  by  agitation  with  petroleum  ether. 
A  factitious  succinic  acid  has  been  prepared  by  adding  a  little  oil  of 
amber  to  tartaric  acid,  ammonium  chloride  or  potassium  hydrogen 
sulphate. 

Inorganic  impurities  and  adulterants  will  be  left  on  igniting  the 
substance.  Cream  of  tartar  leaves  potassium  carbonate  on  ignition; 
it  has  been  found  in  succinic  acid  to  the  extent  of  50%.  Barium  sul- 
phate may  be  recognised  by  its  insolubility  and  other  characters;  and 
boric  acid  by  the  reddish-brown  colour  imparted  to  turmeric  paper, 
when  the  ash  is  acidulated  with  hydrochloric  acid  and  the  solution 
evaporated  in  contact  with  it.  Heavy  metals  may  be  recognised  by 
the  usual  tests. 

Foreign  organic  acids  may  be  detected  by  their  special  reactions. 
Thus  oxalic  acid  will  be  precipitated  on  adding  calcium  acetate  (or 
a  mixture  of  calcium  chloride  and  ammonium  acetate)  to  the  aqueous 
solution  of  the  sample ;  tartaric  acid  by  potassium  acetate  and  alcohol ; 
citric  acid  by  the  precipitate  formed  on  adding  excess  of  lime-water  and 
boiling.  Benzole  acid  may  be  detected  by  its  solubility  in  carbon 
disulphide  or  warm  petroleum  spirit,  and  by  its  separation  on  treating 
the  precipitate  produced  in  the  neutralised  liquid  by  ferric  chloride  with 
hydrochloric  acid. 

Ammonium  chloride  may  be  recognised  by  the  tests  for  ammonium 
salts  and  chlorides. 

Sugar  and  various  other  impurities  cause  charring  on  warming  the 
substance  with  sulphuric  acid. 

A  useful  method  of  examining  succinic  acid  is  to  dissolve  i  grm.  of 
the  sample  in  15  c.c.  of  hot  alcohol  in  which  it  should  be  completely 
soluble.  When  cold,  one-half  the  solution  is  mixed  with  an  equal 
volume  of  chloroform,  and  the  other  with  an  equal  measure  of 
ammonia.  Complete  admixture  should  occur  in  both  cases.  If  the 
result  of  the  test  is  satisfactory,  and  the  sample  leaves  no  sensible 
quantity  of  ash,  and  does  not  notably  darken  with  strong  sulphuric 
acid,  the  substance  may  be  considered  pure. 

Malic  Acid. 

Malic  acid  is  contained  in  apples,  pears  and  many  fruits  used  for 
domestic  purposes.  It  is  usually  prepared  from  rhubarb  stalks  or 
mountain-ash  berries. 


534  ACID    DERIVATIVES    OF    ALCOHOLS. 

Malic  acid  crystallises  in  groups  of  4-  or  6-sided  prisms,  which  are 
colourless  and  odourless,  and  readily  fusible.  Malic  acid  is  deliques- 
cent and  readily  soluble  in  water,  alcohol  and  ether.  The  aqueous 
solution  has  an  agreeable  acid  taste,  and  becomes  mouldy  on  keeping. 
In  contact  with  ferments,  especially  putrid  cheese,  the  solution  of 
malic  acid  yields  succinic  and  acetic  acids  and  sometimes  butyric  acid. 

When  heated  in  a  small  retort  to  about  i8o°,free  malic  acid  melts 
and  evolves  vapours  of  maleic  and  fumaric  acids,  which  crystallise 
on  the  cooler  parts  of  the  retort  and  receiver.  Fumaric  acid,  forms 
slowly  at  150°,  and  mostly  crystallises  in  the  retort,  in  broad,  colour- 
less, rhombic  or  hexagonal,  prisms,  which  vapourise  without  melting 
at  about  200°,  and  are  soluble  in  250  parts  of  cold  water,  and  easily 
in  alcohol  and  ether.  Maleic  acid  is  the  chief  product  if  the  tempera- 
ture be  suddenly  raised  to  200°.  This  body  crystallises  in  oblique 
rhomboidal  prisms,  which  melt  at  130°,  vapourise  at  about  160°,  and 
are  readily  soluble  in  water  and  alcohol.  The  behaviour  of  malic  acid 
on  heating  is  of  value  owing  to  the  few  characteristic  tests  for  this  acid. 
Maleic  and  fumaric  acids  are  stereo-isomers. 

Malic  acid,  exhibits  optical  activity.  It  exists  in  two  forms:  dex- 
trorotatory and  laevorotatory. 

By  the  action  of  hydriodic  acid,  under  pressure,  malic  acid  is  con- 
verted into  succinic  acid.  Nitric  acid  and  alkaline  solutions  of  per- 
manganate oxidise  malic  acid.  Concentrated  sulphuric  acid  darkens 
malic  acid  and  malates  very  slowly  on  warming.  When  boiled  with 
dilute  sulphuric  acid  and  potassium  dichromate,  malic  acid  evolves 
an  odour  of  ripe  fruit. 

No  malate  is  quite  insoluble  in  water,  only  a  few  are  soluble  in 
alcohol.  Solution  of  calcium  chloride  does  not  precipitate  malic  t 
acid  or  malates  in  the  cold  (distinction  from  oxalic  and  tartaric  acids) ; 
only  in  neutral  and  very  concentrated  solutions  is  a  precipitate  formed 
on  boiling.  (Citrates  are  precipitated  from  neutral  boiling  solutions 
by  calcium  chloride,  unless  the  liquid  is  very  dilute.)  The  addition 
of  alcohol  after  calcium  chloride  produces  a  bulky,  white  precipitate 
of  calcium  malate,  even  in  dilute  neutral  solutions.  Thus,  if  the  liquid 
be  filtered  first  cold  (to  remove  oxalic  and  tartaric  acids),  and  then  boil- 
ing hot  (to  remove  citric  acid),  the  malic  acid  can  be  precipitated  on 
addition  of  2  volumes  of  alcohol.  This  precipitate  may  contain  cal- 
cium sulphate  or  succinate,"  but  will  be  free  from  formate,  acetate,  ben- 
zoate  except  that  if  more  than  2  volumes  of  alcohol  are  added,  cal- 


MALIC   ACID.  535 

cium  formate  precipitate.  On  boiling  the  precipitate  with  a  moder- 
ate quantity  of  water,  the  malate  will  be  dissolved,  and  tannate  and 
sulphate  left  almost  wholly  behind.  The  precipitate  produced  by 
calcium  chloride  and  alcohol  may  also  be  tested  for  malic  acid  (after 
drying  it  to  get  rid  of  all  trace  of  alcohol)  by  decomposing  it  with  dilute 
sulphuric  acid,  and  boiling  the  filtered  liquid  with  a  small  quantity  of 
potassium  dichromate.  If  the  liquid  remains  yellow,  succinic  acid 
alone  is  likely  to  be  present;  but  if  green  and  without  odour,  citric  acid 
is  probably  present  either  with  or  without  succinic  acid.  If  the  liquid 
becomes  green  and  evolves  an  odour  of  ripe  fruit,  malic  acid  is  present, 
and  possibly  either  or  both  succinic  and  citric  acid  in  addition. 

Solution  of  lead  acetate  precipitates  malates,  more  perfectly  after 
neutralisation  with  ammonia,  as  a  white  (and  frequently  crystalline) 
precipitate  of  lead  malate,  which,  on  boiling  for  a  few  minutes,  sets 
under  the  liquid  to  a  transparent,  waxy,  semi-solid.  This  character- 
istic reaction  is  obscured  by  the  presence  of  other  organic  acids.  The 
precipitate  is  very  sparingly  soluble  in  cold  water,  somewhat  soluble 
in  hot  water.  Lead  malate  is  soluble  in  strong  ammonia,  but  is  not 
readily  dissolved  by  a  slight  excess.  (Distinction  from  tartrate  and 
citrate.)  It  dissolves  in  ammonium  acetate,  and  on  mixing  the  liquid 
with  2  volumes  of  alcohol  is  reprecipitated.  (Lead  succinate  remains 
in  solution.) 

The  precipitate  of  lead  malate  may  be  washed  with  a  mixture  of  2 
volumes  of  alcohol  and  i  of  wrater. 

If  the  precipitate  of  lead  malate  is  treated  with  excess  of  ammonium 
hydroxide,  dried  on  the  water-bath,  moistened  and  triturated  with 
alcoholic  ammonia,  and  then  treated  with  absolute  alcohol,  only 
ammonium  malate  dissolves;  ammonium  citrate,  tartrate,  and  oxa- 
late,  being  insoluble  in  absolute  alcohol.  Malic  acid  may  be  sepa- 
rated from  other  organic  acids  in  solution  by  adding  ammonium 
hydroxide  in  slight  excess,  and  then  8  or  9  volumes  of  strong  alcohol, 
which  precipitates  all  but  the  ammonium  malate.  The  method  may 
be  conveniently  applied  to  the  solution  of  the  acids  obtained  by  sus- 
pending the  lead  salts  in  water  and  passing  hydrogen  sulphide  through 
the  liquid. 

If  the  alcoholic  solution  of  ammonium  malate  is  precipitated  by 
lead  acetate,  and  the  lead  malate  obtained  filtered  off,  washed  with 
alcohol,  dried  at  100°  and  weighed,  the  weight  obtained,  multiplied 
by  0.3953,  gives  the  quantity  of  malic  acid  present. 


536  ACID    DERIVATIVES    OF   ALCOHOLS. 

For  the  estimation  of  malic  acid  in  wine,  see  page  187;  for  estima- 
tion in  vinegar  see  page  505. 

Tartaric  Acid, 

Tartaric  acid  occurs  in  some  plant  juices.  Grape  juice  is  the  only 
important  source.  The  deposit  formed  on  the  sides  and  bottom  of  the 
vessels  in  which  wine  is  manufactured  consists  largely  of  calcium  and 
potassium  tartrates.  After  purification,  it  is  treated  with  calcium 
carbonate  and  calcium  sulphate,  by  which  a  nearly  insoluble  calcium 
tartrate  is  produced,  and  this,  when  decomposed  with  sulphuric  acid, 
yields  free  tartaric  acid,  which  is  obtained  in  crystals  by  cooling  the 
concentrated  liquid. 

Three  distinct  forms  of  tartaric  acid  exist.  Their  chief  physical 
and  chemical  differences  are  as  follows: 

Dextrotartaric,  ordinary  tartaric  acid,  forms  anhydrous,  hemi- 
hedral,  monoclinic  crystals,  the  aqueous  solution  of  which  turns  the 
plane  of  polarisation  to  the  right,  the  value  for  [a]j)  at  16°  being  13.1° 
for  a  15%,  and  14.7°  for  a  2%  solution.  The  crystals  fuse  at  135°, 
have  a  sp.  gr.  of  1.74  to  1.76,  and  are  readily  soluble  in  absolute  and 
dilute  alcohol. 

In  the  following  article  this  acid  and  its  salts  are  always  referred  to 
unless  otherwise  stated. 

Laevotartaric  acid  forms  anhydrous  crystals,  the  aqueous  solution 
of  which  turns  the  plane  of  polarisation  of  a  luminous  ray  to  the  left, 
the  rotation  being  equal  and  opposite  to  that  produced  by  dextro- 
tartaric  acid. 

Inactive,  or  mesotartaric  acid,  is  produced  by  prolonged  heating 
of  dextrotartaric  acid  to  165°  with  a  small  proportion  of  water.  It  is 
optically  inactive,  but  unlike  racemic  acid  is  not  resolvable  into  2  acids. 
Mesotartaric  acid  is  very  soluble  in  water,  forms  crystals  containing 
i  molecule  of  water,  and  yields  calcium  and  potassium  hydrogen  salts 
more  soluble  than  the  corresponding  salts  of  ordinary  tartaric  acid. 

Racemic  acid,  often  described  as  a  fourth  form  of  tartaric  acid,  is 
really  an  association  of  equal  quantities  of  the  active  forms  and  is 
optically  inactive.  It  can  be  separated  into  the  two  forms  and,  can 
also  be  obtained  by  mixing  equal  amounts  of  them.  It  occurs  with 
ordinary  tartaric  acid  in  crude  tartars.  It  forms  crystals  containing 
i  mol.  of  water,  which  effloresce  in  the  air,  and  become  completely 
anhydrous  at  100°;  the  resultant  anhydrous  acid  melts  at  about  200°. 
Racemic  acid  is  soluble  in  5  parts  of  cold  water,  and  with  difficulty 


TARTARIC   ACID.  537 

in  cold  alcohol.  The  calcium  racemate  is  less  soluble  in  water  than 
calcium  dextrotartrate,  and  is  also  distinguished  by  its  insolubility  in 
acetic  acid  and  in  ammonium  chloride  solution. 

The  slighter  solublitiy  of  calcium  racemate  as  compared  with  cal- 
cium dextrotartrate  has  led  to  the  suggestion  of  a  method  for  detecting 
the  latter  by  adding  a  solution  of  laevotartaric  acid  to  the  liquid  to  be 
tested,  then  calcium  chloride  and  neutralizing  the  solution.  The 
laevotartaric  acid  will  associate  with  an  equal  portion  of  dextrotartaric 
acid,  if  any  is  present,  and  the  highly  insoluble  calcium  salt  will 
precipitate. 

Ordinary  tartaric  acid  is  soluble  in  0.7  part  of  cold  and  0.5  part  of 
boiling  water;  in  1.6  parts  of  cold  alcohol  (95%)  and  in  about  0.2  part 
of  boiling  alcohol;  in  250  parts  of  ether,  and  is  nearly  insoluble  in 
chloroform,  benzene  and  petroleum  spirit. 

The  followin'g  table  by  H.  Schiff  shows  the  sp.  gr.  of  aqueous  solu- 
tions of  tartaric  acid: 

Percentage  by  weight  of  tartaric  acid.  sp.  gr.  at  15° 

33  1-1654 

22  I.IO62 

14.67  1.0690 

II  I-05II 

7-33  J-°337 

3.67  1.0167 

/ 

Unsterilized  aqueous  solutions  of  tartaric  acid  (especially  when  di- 
lute) gradually  decompose  on  account  of  the  growth  of  mold.  The 
change  may  be  prevented  by  the  addition  of  a  little  phenol.  Many 
tartrates  decompose  when  kept  in  a  moist  state. 

Most  oxidising  agents  convert  tartaric  into  formic  acid.  Ammonio- 
silver  nitrate  is  reduced  with  formation  of  carbonic  and  oxalic  acids. 
In  dilute  solution,  tartaric  acid  reduces  gold  and  platinum  chlorides, 
and  converts  mercuric  chloride  into  calomel. 

Detection  and  Estimation  of  Tartaric  Acid  and  Tartrates. — 
Tartaric  acid  and  tartrates  are  charred  when  heated  with  concentrated 
sulphuric  acid  of  1.845  SP-  gr-  The  reaction  may  be  used  to  distinguish 
a  tartrate  from  a  citrate  or  to  detect  tartaric  acid  in  presence  of  citric 
acid.  For  this  purpose,  i  grm.  of  the  sample  should  be  treated  with 
10  c.c.  of  pure  concentrated  sulphuric  acid  (free  from  nitrous  com- 


ACID    DERIVATIVES    OF    ALCOHOLS. 

pounds),  and  the  mixture  heated  to  100°  for  40  minutes.  Citric  acid 
gives  only  a  yellow  colour  when  thus  treated,  but  if  i%  of  tartaric  acid 
be  present  the  liquid  has  a  distinct  brown  shade,  and  this  becomes 
still  more  marked  with  larger  proportions. 

If  a  drop  of  ferrous  sulphate  solution  is  added  to  a  solution  of  tar- 
taric acid  or  soluble  tartrate,  then  a  few  drops  of  hydrogen  peroxide, 
and  the  mixture  finally  treated  with  excess  of  sodium  hydroxide,  a 
fine  violet  is  produced,  which  in  strong  solutions  is  so  deep  as  to  appear 
almost  black.  The  colour  is  discharged  by  sulphurous  acid.  If  potas- 
sium ferrocyanide  is  added  to  the  violet  liquid,  and  then  sufficient 
dilute  sulphuric  acid  to  acidify  the  solution,  the  iron  may  be  filtered  off 
and  a  colourless  filtrate  obtained  which  again  gives  the  violet  colour  on 
addition  of  a  ferrous  salt.  The  colourless  filtrate  reduces  silver  and 
mercury  compound,  potassium  dichromate  and  permanganates. 
After  adding  excess  of  alkali  it  precipitates  cuprous  oxide  fromFehling's 
solution  in  the  cold;  on  heating,  metallic  copper  is  separated. 

Acid  solution  of  a  permanganate  or  sodium  hypochlorite  may  be 
substituted  for  the  hydrogen  peroxide  in  the  foregoing  test,  if  care  be 
taken  to  avoid  excess,  but  the  result  is  not  so  satisfactory.  Heavy 
metals  and  oxidising  agents  must  be  absent.  Citric,  malic,  succinic, 
oxalic  and  acetic  acids  and  sugar  were  found  by  H.  J.  H.  Fenton,  the 
observer  of  the  reaction,  to  give  no  similar  colouration  (Chem.  News, 
1876,  33,  190;  1881,  43,  no). 

Soluble  tartrates  in  neutral  solution  give  white  calcium  tartrate 
on  addition  of  calcium  chloride.  The  precipitate  is  nearly  insoluble 
in  cold  water;  soluble  in  many  ammonium  salts;  soluble  (after  wash- 
ing) in  a  cold  solution  of  sodium  hydroxide,  but  reprecipitated  on 
boiling;  soluble  in  acids  (including  acetic);  and  converted  by  heating 
with  a  neutral  solution  of  copper  chloride  into  insoluble  copper  tartrate. 
Calcium  citrate  yields  soluble  copper  citrate.  Calcium  tartrate 
may  also  be  conveniently  examined  by  dissolving  it  in  the  smallest  pos- 
sible quantity  of  acetic  acid,  adding  excess  of  potassium-chloride  solu- 
tion and  stirring  vigorously,  when  the  potassium  hydrogen  tartrate  will 
be  thrown  down. 

The  reducing  action  of  tartaric  acid  on  silver  compounds  is  a  deli- 
cate test,  but  is  liable  to  failure  if  certain  conditions  are  not  observed. 
The  solution  of  tartaric  acid,  or  alkali-metal  tartrate  (all  other  metals 
being  first  removed),  is  rendered  acid  with  nitric  acid,  excess  of  silver 
nitrate  added,  and  any  precipitate  filtered  off.  To  the  solution,  very 


TARTARIC   ACID.  539 

dilute  ammonium  hydroxide  is  added  until  the  precipitate  at  first  formed 
is  nearly  redissolved.  The  solution  is  again  filtered,  and  the  filtrate 
heated  nearly  to  boiling  for  a  few  minutes,  when  a  brilliant  mirror  will 
be  formed  on  the  sides  of  the  tube.  Citric  acid  does  not  reduce  silver 
under  similar  circumstances,  but  gives  a  precipitate  on  continued 
boiling. 

Tartaric  acid  prevents  the  precipitation  of  many  metallic  solutions 
by  alkalies,  stable  double  tartrates  being  formed.  For  the  separation 
of  heavy  metals  from  tartrates,  hydrogen  sulphide  or  sodium  sulphide 
must  be  employed,  according  to  the  metals  present.  The  filtrate 
may  be  concentrated,  and  any  barium,  strontium,  calcium  or  magne- 
sium present  thrown  down  by  boiling  with  sodium  carbonate.  Alu- 
minum is  not  separated  by  either  of  the  above  precipitants,  but  the 
tartaric  acid  can  be  detected  and  estimated  in  the  solution  without 
removing  it. 

The  best  method  of  direct  estimation  of  tartaric  acid  is  to  pre- 
cipitate it  in  the  form  of  potassium  hydrogen  tartrate.  When  the  free 
acid  is  to  be  estimated,  either  alone  or  mixed  only  with  citric  acid, 
the  method  described  under  Citric  Acid  should  be  employed.  For 
the  estimation  of  tartaric  acid  in  tartrates  and  in  the  various  natural 
and  artificial  products  of  tartaric  acid  manufactories,  processes  are 
given  below. 

Tartaric  acid  in  wine  may  exist  in  the  free  state,  and  as  calcium  and 
potassium  hydrogen  tartrates,  and  ethyl  tartrate  is  probably  often 
present.  (See  page  177.) 

Like  the  corresponding  salts  of  other  organic  acids,  tartrates  con- 
taining metals  not  easily  reducible,  leave  on  gentle  ignition  a  residue  of 
carbonate  or  oxide  and  by  dissolving  this  residue  in  standard  acid  and 
ascertaining  the  amount  of  acid  neutralized  by  titrating  the  excess  with 
standard  alkali,  an  accurate  estimation  can  be  effected,  and,  if  it  is 
known  whether  the  tartrate  was  originally  acid  or  neutral  an  esti- 
mation of  the  acid  itself  is  obtained. 

Tartaric  acid  and  hydrogen  tartrates  neutralise  alkalies  completely. 

The  tartaric  acid  in  tartrates  containing  organic  bases  may  generally 
be  ascertained  by  precipitation  as  potassium  hydrogen  tartrate. 

The  alkyl  tartrates  are  unimportant.  Ethyl  tartrate  may  be  decom- 
posed by  heating  with  alcoholic  sodium  hydroxide  and  potassium 
hydrogen  tartrate  precipitated  by  adding  excess  of  acetic  acid. 

Commercial  tartaric  acid  is  liable  to  contain  the  same  impurities 


540  ACID    DERIVATIVES    OF   ALCOHOLS. 

as  citric  acid,  and  is  examined,  in  a  similar  manner.  It  may  be  adul- 
terated with  alum  and  potassium  hydrogen  sulphate,  the  presence  of 
either  of  which  would  be  indicated  by  the  ash  left  on  ignition  and 
the  formation  of  a  precipitate  on  addition  of  barium  chloride  to  the 
aqueous  solution. 

Tartaric  acid  liquors  are  the  liquids  resulting  from  the  decomposi- 
tion of  calcium  tartrate  by  sulphuric  acid.  They  are  of  a  very  complex 
character,  containing:  free  tartaric  acid;  foreign  organic  acids;  sul- 
phuric acid,  and  calcium,  potassium,  iron  and  aluminum  sulphates; 
phosphates;  and  bodies  of  an  indefinite  nature.  The  analytic  exam- 
ination usually  includes  estimation  of  the  tartaric  and  free  sulphuric 
acid,  with  the  additional  estimation,  in  some  cases,  of  the  total  organic 
acids. 

The  estimation  of  the  tartaric  acid  is  best  effected  by  precipitation 
as  potassium  hydrogen  tartrate.  Potassium  acetate  is  the  best  reagent 
for  pure  liquors,  but  it  is  inapplicable  in  presence  of  iron  or  aluminum. 
Potassium  citrate  is  free  from  this  objection.  It  is  obtained  by  neu- 
tralising citric  acid  by  pure  potassium  carbonate  or  hydroxide  and  is 
best  employed  in  the  following 'manner : 

A  quantity  of  liquor,  of  30  to  40  c.c.  in  volume,  as  cold  as  possible, 
and  containing  from  2  to  4  grm.  of  tartaric  acid,  is  treated  with  a 
saturated  aqueous  solution  of  the  citrate,  added  drop  by  drop  with  con- 
stant stirring.  As  soon  as  the  free  sulphuric  acid  is  neutralised  the 
precipitate  begins  to  appear  in  streaks  on  the  sides  of  the  glass.  In 
presence  of  much  sulphuric  acid,  a  fine  precipitate  of  potassium  sul- 
phate will  precede  the  formation  of  the  tartrate,  but  is  readily  dis- 
tinguished therefrom.  When  the  streaks  begin  to  appear,  i  c.c.  of 
citrate  solution  is  added  for  every  grm.  of  tartaric  acid  supposed  to  be 
present.  A  great  excess  should  be  avoided.  Should  a  gelatinous 
precipitate  be  formed,  the  experiment  is  repeated  with  a  previous 
addition  of  some  citric  acid.  After  stirring  continuously  for  10  min- 
utes, the  precipitate  is  washed  2  or  3  times  with  25  c.c.  of  a  5%  solution 
-of  potassium  chloride,  saturated  with  potassium  hydrogen  tartrate. 
The  precipitate  is  then  collected  on  a  small  filter  and  washed  with  the 
same  solution,  until  the  acidity  of  the  filtrate  is  only  slightly  in  excess  of 
that  of  the  solution  used  for  washing  the  precipitate.  The  filter  and 
precipitate  are  finally  transferred  to  a  beaker,  and  the  amount  of  tartaric 
acid  present  is  determined  by  titration  with  standard  alkali  set  against 
potassium  hydrogen  tartrate;  litmus  or  phenolphthalein  being  used  as 


TARTARIC    ACID.  541 

the  indicator.  The  presence  of  potassium  sulphate  in  the  precipitate 
is  of  no  consequence,  as  it  has  no  neutralising  power. 

Sometimes,  however,  a  potassium  hydrogen  citrate  is  carried  down  by 
the  tartrate  and  obstinately  retained.  It  is  best  got  rid  of  by  dissolv- 
ing the  precipitate  in  50  c.c.  of  hot  water,  adding  5  grm.  of  potassium 
chloride,  and  cooling  the  liquid  quickly  to  15°,  stirring  continually,, 
and  continuing  the  agitation  for  10  minutes.  This  purified  precipitate 
may  be  washed  with  the  ordinary  washing  fluid  with  great  ease,  but  a. 
correction  of  1/2  %  on  the  tartaric  acid  found  must  be  made  for  un- 
avoidable loss  in  the  process  of  purification.  The  filtrate  may  be  tested 
for  citric  acid  by  neutralising  it  with  sodium  hydroxide  and  adding 
calcium  chloride.  After  prolonged  standing  in  the  cold  and  filtration 
from  a  little  calcium  tartrate,  the  solution  is  boiled,  when  any  precipi- 
tate will  consist  of  calcium  citrate. 

Under  favourable  circumstances,  assays  by  the  above  method 
show  from  99  to  100%  of  the  tartaric  acid  present,  but  greater  differ- 
ences occur  if  the  proper  proportion  of  citrate  is  not  used.  Grosjean 
concluded  that,  when  an  accurate  assay  of  factory  tartaric  acid  liquors 
is  required,  a  preliminary  series  of  experiments  was  necessary  to  ascer- 
tain what  volume  of  citrate  solution  gave  a  precipitate  of  maximum 
acidity.  This  having  been  ascertained,  a  final  experiment  should  be 
made,  using  the  proper  quantity  of  citrate  solution,  and  washing  the 
precipitate  very  thoroughly.  In  presence  of  much  sulphuric  acid,  the 
results  have  a  tendency  to  be  in  excess  of  the  truth.  From  very  old  bad 
liquors,  potassium  alum  may  be  precipitated  on  adding  the  citrate 
solution,  owing  to  the  formation  of  potassium  sulphate  and  the 
sparing  solubility  of  alum  in  solutions  of  that  salt.  When  alum  has 
been  precipitated  the  results  will  be  below  the  truth,  as  on  washing 
with  the  potassium  chloride  solution  a  fluid  is  formed  in  which  potas- 
sium hydrogen  tartrate  is  readily  soluble.  If,  on  the  other  hand,  an  alco- 
holic washing  liquid  be  substituted,  the  alum  is  retained  in  the  pre- 
cipitate, and  increases  the  final  acidity.  The  difficulty  may  be 
avoided  by  adding  phosphoric  acid  before  the  citrate  solution,  but 
the  filtration  must  be  effected  immediately  after  the  stirring,  or  a  gela- 
tinous precipitate  of  aluminum  phosphate  may  be  thrown  down. 

Racemic  acid,  if  present,  will  be  estimated  as  tartaric  acid  by  the 
above  method.  Inactive  tartaric  acid  is  only  imperfectly  precipitated,, 
owing  to  the  greater  solubility  of  potassium  salt.  Oxalic  acid  has  been 
detected  in  old  liquors,  but  does  not  interfere  with  the  results. 


542  ACID    DERIVATIVES    OF    ALCOHOLS. 

The  estimation  of  the  free  sulphuric  acid  in  tartaric  acid  liquors 
is  troublesome,  owing  to  the  insolubility  of  potassium  and  calcium  tar- 
trates  in  alcohol  arid  the  occasional  presence  of  alum.  Thus,  it 
mixed  solutions  of  potassium  alum  and  tartaric  acid  are  treated  with 
alcohol,  potassium  hydrogen  tartrate  and  alum  are  precipitated,  and 
the  liquid  contains  sulphuric  acid,  which  was  not  present  originally. 
A  similar  reaction  occurs  if  calcium  sulphate  is  substituted  for  the 
alum.  These  errors  are  removed  when  the  quantity  of  sulphuric 
acid  in  the  liquor  is  sufficiently  great,  and  will  occur  in  practice  merely 
in  the  case  of  new  liquors  of  bad  quality.  (For  analytic  process  see 

P-  549-) 

A  useful  indication  of  the  presence  of  sulphuric  acid  in  tartaric 
acid  liquors  is  obtained  by  treating  the  liquid  with  half  its  measure  of 
a  saturated  aqueous  solution  of  calcium  chloride.  A  turbidity  due  to 
calcium  sulphate  occurs  immediately  in  a  liquor  containing  sulphuric 
acid  equivalent  to  0.8%  of  brown  oil  of  vitriol,  and  in  5  minutes  when 
only  0.1%  of  oil  of  vitriol  is  present. 

For  the  estimation  of  the  total  organic  acids  in  tartaric  acid  liquors, 
R  Warington  recommends  the  following  method  (Jour.  Chem.  Soc., 
1876,  28,  982:  Exactly  neutralise  a  known  measure  of  the  liquor 
with  standard  caustic  alkali,  evaporate  to  dryness,  and  ignite  the  resi- 
due at  a  very  low  temperature  till  the  carbon  is  nearly  consumed. 
Treat  the  ash  with  a  known  quantity  of  standard  sulphuric  acid,  heat 
and  decant,  and  treat  the  insoluble  residue  with  more  standard  acid, 
concentrating,  if  necessary,  to  effect  solution  of  the  phosphates.  Treat 
the  mixed  cold  concentrated  solutions  with  sufficient  potassium  sodium 
tartrate  to  keep  any  aluminum  in  permanent  solution,  and  then  titrate 
the  solution  with  standard  alkali  and  litmus.  The  amount  of  standard 
sulphuric  acid  neutralised  by  the  ash  is  the  exact  equivalent  of  the 
total  organic  acid  in  the  liquor  taken,  and  each  c.c.  of  normal  acid 
neutralised  represents  0.075  grm-  °f  organic  acid,  expressed  in  terms  of 
tartaric  acid. 

Lees;  Argol;  Tartar. — These  are  products  of  the  fermentation  of 
grape-juice;  they  consist  largely  of  potassium  hydrogen  tartrate  and 
are  the  materials  from  which  tartaric  acid  and  tartrates  are  obtained. 
Their  separation  is  due  to  the  diminished  solubility  of  the  tartrates 
in  the  alcoholic  liquid  produced  by  the  fermentation. 

Lees  is  the  solid  matter  collected  from  the  bottom  of  the  vessels  in 
which  tjie  grape-juice  is  fermented. 


TARTARIC   ACID.  543 

Its  composition  is  greatly  altered  by  "plastering"  the  wine.  This 
process  consists  in  adding  to  the  wine  an  impure  calcium  sulphate 
containing  some  carbonate.  "  Spanish  earth,"  a  kind  of  readily  de- 
composed clay,  is  sometimes  employed.  The  result  is,  that  in  plastered 
lees  the  tartrate  exists  chiefly  as  the  calcium  tartrate  instead  of  the  acid 
potassium  salt.  The  total  tartaric  acid  in  lees  is  usually  from  24  to  32%. 
Lees  contain  from  30  to  40%  of  indefinite  vegetable  matter,  the  remain- 
der being  tartrates,  sulphates  (in  plastered  lees),  ferric  oxide  alumina, 
phosphates  and  sometimes  lumps  of  plaster. 

Argol,  or  crude  tartar,  is  the  crystalline  crust  deposited  on  the 
sides  of  the  vessels  used  for  the  fermentation.  It  exhibits  some  irregu- 
larity of  composition,  the  tartaric  acid  ranging  from  40  to  70%,  most 
of  it  as  potassium  hydrogen  tartrate.  Very  low  argols  resemble  superior 
lees,  while  first-class  argols  are  equal  to  ordinary  refined  tartar.  The 
term  "argol"  is  also  applied  loosely  to  both  tartar  and  lees.  In  argol, 
globules  of  sulphur  are  sometimes  found;  they  are  due  to  the  sulphur 
burnt  in  the  casks  before  introducing  the  wine. 

Cream  of  tartar,  or  refined  tartar,  is  prepared  by  boiling  crude 
tartar  (argol)  with  water,  filtering  and  crystallising  the  salt  from  the 
•clear  liquid.  The  term  cream  of  tartar  is  derived  from  the  fact  that 
during  the  evaporation  of  the  liquid  the  salt  collects  in  white  crystalline 
crusts  on  the  surface  of  the  solution.  Cream  of  tartar  consists  chiefly 
of  potassium  hydrogen  tartrate,  but  contains  more  or  less  calcium 
tartrate,  which,  though  nearly  insoluble  in  pure  water,  dissolves  with 
moderate  facility  in  a  hot  solution  of  potassium  hydrogen  tartrate. 
The  proportion  of  calcium  tartrate  usually  present  in  commercial 
cream  of  tartar  ranges  from  2  to  9%;  proportion  in  excess  of  10%  may 
be  considered  as  an  adulterant  (see  a  paper  by  Allen,  Analyst,  1880. 
5,  114).  Commercial  cream  of  tartar  is  adulterated  to  a  considerable 
extent,  the  potassium  and  calcium  sulphates,  marble,  alum  and  barium 
sulphate,  starch  and  calcium  phosphate  being  among  the  substances 
used,  and  potassium  hydrogen  sulphate  is  sold  under  the  name  of 
"tartalie,"  and  employed  as  a  substitute  for  cream  of  tartar.  It  has  a 
higher  neutralising  power  than  cream  of  tartar,  and  hence  is  some- 
times diluted  with  potato  starch,  the  mixture  being  sold  under  mis- 
leading names.  Powdered  alum  is  often  sold  under  the  term  C.  T.  S. 
(cream  of  tartar  substitute). 

Assay  of  Tartar  and  Argol. — For  the  detection  of  adulterants  in 
cream  of  tartar,  the  following  tests  may  be  applied: 


544  ACID    DERIVATIVES    OF    ALCOHOLS. 

The  sample  should  be  ignited,  the  residue  boiled  with  water,  filtered 
off,  washed,  ignited,  moistened  with  ammonium  carbonate,  gently  re- 
ignited  and  weighed.  The  " insoluble  ash"  thus  obtained  from  genu- 
ine cream  of  tartar  consists  of  the  calcium  carbonate  corresponding 
to  the  calcium  tartrate  originally  present,  and  its  weight  may  be  calcu- 
lated to  its  equivalent  of  the  latter  by  multiplying  it  by  the  factor  1.88. 
The  calcium  tartrate  thus  found  should  not  exceed  10%,  or  12%  at  the 
outside.  Any  higher  proportion  is  usually  due  to  adulteration  with 
calcium  compounds.  Addition  of  calcium  chloride  is  said  to  have 
occurred,  though  improbable,  but  there  are  authentic  cases  of  adultera- 
tion by  chalk  and  marble.  Allen  found  20%  of  calcium  sulphate 
probably  added  as  plaster  of  Paris.  In  the  case  of  adulterated  samples, 
the  proportion  of  calcium  tartrate  cannot  be  deduced  with  accuracy 
from  the  percentage  of  " insoluble  ash." 

The  sample  is  boiled  with  a  moderate  excess  of  pure  sodium  car- 
bonate and  the  liquid  filtered.  A  portion  of  the  filtrate  is  tested  for 
sulphates  (e.  g.,  calcium  sulphate,  potassium  sulphate  and  alum) 
by  acidulating  slightly  with  hydrochloric  acid  and  adding  barium 
chloride,  and  another  for  chlorides  by  rendering  it  acid  with  nitric  acid, 
and  adding  silver  nitrate;  traces  of  sulphates  and  chlorides  may  be 
neglected.  The  precipitate  produced  by  sodium  carbonate  should  be 
rinsed  off  the  filter  and  treated  with  dilute  hydrochloric  acid.  Any  in- 
soluble residue  may  consist  of  sand  or  barium  sulphate.  Both  the  chemi- 
cal and  microscopical  characters  may  be  employed  to  distinguish 
these,  and  to  determine  whether  the  latter  adulterant  is  crystalline  or 
amorphous. 

The  presence  of  alum  is  indicated  by  the  detection  of  a  notable 
quantity  of  sulphates,  and  the  presence  of  aluminum  oxide  in  the 
insoluble  ash.  Aluminum  hydroxide  cannot  be  precipitated  by  add- 
ing ammonium  hydroxide  to  the  original  solution  of  the  substance, 
owing  to  the  presence  of  tartrate;  but  it  may  be  detected  by  neutralising 
the  hot  solution  of  the  sample  with  sodium  hydroxide,  and  boiling  the 
liquid  with  a  little  acetic  acid  and  excess  of  sodium  phosphate.  Any 
aluminum  present  will  be  thrown  down  as  phosphate,  tartrates  having 
scarcely  any  solvent  action  on  the  precipitate  at  the  temperature  of 
ebullition,  and  in  presence  of  excess  of  phosphoric  acid.  Alum  may 
be  dissolved  out  of  cream  of  tartar  by  treating  the  finely  powdered 
sample  with  a  cold,  saturated,  aqueous  solution  of  potassium  hydrogen, 
tartrate,  containing  5%  of  potassium  chloride. 


TARTARIC   ACID.  545 

Starch  is  easily  detected  by  microscopic  examination  and  the 
iodine  test.  For  estimation  see  under  "Starch." 

Calcium  phosphates  are  detected  and  determined  by  treating  0.5 
grm.  with  excess  of  moderately  strong  nitric  acid,  and  precipitating  with 
ammonium  molybdate  in  the  usual  way. 

Assay  of  Crude  Tartars. — The  examination  may  be  made  either  to 
determine  the  potassium  hydrogen  tartrate  present  or  the  total  tartaric 
acid  that  will  be  yielded  by  the  sample. 

Estimation  of  Potassium  Hydrogen  Tartrate. — Oulman's  method 
(Lunge,  Chem.  Techn.  Unters.  Meth.,  Vol.  3): 

0.376  grm.  of  the  finely-powdered  sample  are  put  into  a  1000  c.c. 
flask  with  750  c.c.  of  water,  boiled  for,  at  most,  5  minutes,  made  up  to 
the  mark,  cooled,  again  made  up  to  the  mark,  mixed  and  500  c.c.  of 
filtrate  collected  through  a  dry  filter.  This  filtrate  is  evaporated  to 
dryness  in  a  porcelain  basin  on  the  water-bath.  While  the  dry  mass 
is  still  warm,  it  is  moistened  with  5  c.c.  of  water  cooled  and  100  c.c. 
of  alcohol  added,  the  mixture  thoroughly  stirred  and  allowed  to  stand 
for  30  minutes.  The  alcohol  is  then  decanted  through  a  dry  filter, 
and  the  last  portion  drawn  through  with  the  pump.  Any  acid  potas- 
sium tartrate  on  the  filter  is  washed  back  into  the  evaporating  basin 
with  boiling  water,  the  solution  diluted  with  water  to  make  100  c.c. 
and  titrated  with  N/5  alkali.  0.2  c.c.  should  be  added  to  the  titration 
figure  for  correction. 

Total  Tartaric  Acid.— 

The  following  process  for  analysis  of  tartar  is  designated  "  Golden- 
berg  1907"  (Zeit.,  anal.  Chem.,  1908,  47,  57),  and  was  approved  at 
the  7th  International  Congress  of  Applied  Chemistry,  London,  1909. 
It  is  now  in  general  use. 

A  weighed  amount  of  the  sample  (6  grm.  if  the  tartaric  acid  yield 
is  likely  to  be  above  45  %;  12  grm.  if  below  that  amount)  is 
treated  with  18  c.c.  of  hydrochloric  acid  (sp.  gr.  i.i)  for  10  minutes. 
The  whole  mass  is  then  rinsed  into  a  200  c.c.  measuring  flask,  made 
up  to  the  mark  with  distilled  water,  shaken  well  and  filtered  through 
a  dry  filter  into  a  dry  flask.  10  c.c.  of  potassium  carbonate  solution 
(66  grm.  of  absolute  carbonate  in  100  c.c.)  are  placed  in  a  300  c.c. 
beaker  and  100  c.c.  of  the  filtered  liquid  added.  The  capacity  of  the 
pipette  by  which  this  volume  is  measured  must  correspond  exactly 
with  that  of  the  flask.  The  mixture  is  brought  to  boiling  and  kept 
at  that  point  for  20  minutes,  until  the  calcium  carbonate  has  separated 
VOL.  1-35 


546  ACID    DERIVATIVES    OF    ALCOHOLS. 

in  crystalline  form.  The  liquid  and  precipitate  are  washed  into  a 
200  c.c.  flask,  cooled,  made  up  to  the  mark,  shaken  well  and  filtered 
through  a  dry  filter.  A  volume  of  100  c.c.  of  the  filtrate  is  placed 
in  a  porcelain  basin  or  Jena  flask  and  evaporated  on  the  hot  plate 
to  15  c.c.  and,  while  the  liquid  is  hot,  3.5  c.c.  of  glacial  acetic  acid  are 
added  gradually  and  with  constant  stirring  which  is  continued  for 
five  minutes  after  all  the  acid  has  been  added.  After  10  minutes' 
standing,  10  c.c.  of  alcohol  (95%)  are  added  and  the  liquid  stirred 
for  another  5  minutes,  and  after  standing  for  another  10  minutes 
the  liquid  is  filtered  by  the  aid  of  a  pump  and  washed  with  alcohol 
until  the  washings  are  no  longer  acid.  (See  below.)  The  filter  and 
precipitate  are  transferred  by  the  aid  of  200  c.c.  of  hot  water  into  a 
porcelain  basin,  the  liquid  brought  to  boiling  and  titrated  with  N/5 
alkali  and  neutral  litmus-paper.  The  alkali  must  be  standardised  with 
the  same  paper,  using  pure  potassum  hydrogen  tartrate.  As  the 
volume  of  undissolved  matter  is  disregarded  in  making  up  the  dilu- 
tions, an  allowance  must  be  made.  It  is  agreed  that  for  samples 
yielding  less  than  45%  of  acid,  0.8  should  be  deducted;  for  samples 
yielding  from  45%  to  60%,  0.3  should  be  deducted;  for  those  yield- 
ing 60%  to  70%,  0.2  should  be  deducted;  for  yields  over  70%  no 
deduction  is  made. 

To  control  the  washings  it  is  advised  that  30  c.c.  of  the  alcohol 
that  is  to  be  used  should  be  titrated  with  standard  alkali,  using  phenol- 
phthalein,  and  that  the  washing  should  be  continued  until  30  c.c.  of 
the  filtrate  require  the  same  amount  of  standard  alkali  (with  phenol- 
phthalein)  to  give  the  color  that  was  produced  in  the  test  of  the 
original  30  c.c.. 

Porcelain  dishes  marked  with  a  ring  at  the  volume  of  15  c.c.  can  be 
obtained. 

Warringtorfs  Method  for  Wine  Lees. — Place  8  grm.  of  the  sample 
in  a  beaker,  moisten  with  water  and  heat  on  water-bath  about  5 
minutes.  Add  2  grm.  of  potassium  oxalate  and  heat  the  mixture 
15  minutes  on  water-bath.  While  hot  almost  exactly  neutralise  with 
potassium  hydroxide  solution  (3.5%  solution),  taking  care  not 
to  neutralise  completely,  and  avoiding  an  excess  of  alkali.  The 
quantity  of  alkali  used  is  about  0.5%  short  of  that  required  for 
complete  neutralisation,  as  ascertained  by  a  separate  experiment 
(see  below).  After  neutralisation  in  this  way,  heat  on  water-bath 
about  30  minutes  and  filter,  preferably  on  filter  pump,  using  porcelain 


TARTARIC    ACID.  ,  547 

plate  2.5  cm.  diameter.  (For  difficulties  experienced  with  slow  filtering 
material  see  Grosjean,  Trans.,  1879.)  Wash  with  10  lots  of  water, 
using  3  c.c.  at  a  time.  This  should  be  sufficient,  and  the  filtrate  should 
have  a  volume  of  about  50  c.c.  Make  to  this  volume  either  by  addition 
of  water  or  by  evaporation.  Add  5  grm.  potassium  chloride  and  2.5 
grm.  citric  acid,  stir  well  continuously  during  10  minutes  and  let 
stand.  Filter  off  the  potassium  hydrogen  tartrate  on  pump,  wash 
with  a  10%  solution  of  potassium  chloride  saturated  with  potassium 
hydrogen  tartrate,  of  which  the  acidity  has  been  ascertained  by  N/io 
alkali.  When  the  acidity  of  the  washings  is  the  same  as  that  of  the 
washing  solution,  dissolve  the  precipitate  in  hot  water  and  titrate  with 
N/io  potassium  hydroxide. 

For  Tartars. — Use  3  grm.  and  proceed  as  above. 

Preliminary  Determination  of  Acidity. — Extract  exactly  3  grm.  of 
the  sample  by  boiling  with  water,  decanting,  again  boiling  and  again 
decanting.  The  residue  is  transferred  to  filter-paper  and  thoroughly 
washed  until  the  washings  are  no  longer  acid,  titrated  with  N/io 
alkali  or  with  3.5%  potassium  hydroxide  solution,  using  neutral 
litmus-paper. 

The  following  special  precautions  applicable  to  the  above 
processes  are  taken  from  Rasch's  book  (Die  Fabrikation  der 
Weinsaure) : 

The  sample  must  be  ground  very  fine.  The  alcohol  and  water  must 
be  neutral  to  the  indicators  employed.  The  potassium  carbonate 
should  be  pure,  especially  free  from  iron  and  aluminum.  The 
procedures  must  be  at  ordinary  temperature  unless  otherwise  directed. 
The  evaporation  of  the  solution  containing  potassium  carbonate 
must  not  be  carried  too  far  and  the  treatment  with  acetic  acid 
must  be  while  the  liquid  is  hot.  These  conditions  are  necessary 
to  secure  crystalline  precipitates.  The  acetic  acid  must  not  be 
below  98  r , . 

The  washing  with  alcohol  must  be  carefully  carried  out.  It  is  best 
to  stir  the  precipitate  with  the  stream  from  the  jet  of  the  washbottle, 
and  then  wash  the  funnel  margin  above  the  filter.  Usually  it  will  be 
sufficient  to  fill  the  filter  in  this  manner  3/4  full  five  successive  times. 

The  standard  potassium  hydroxide  must  be  free  from  carbonate 
and  be  accurately  titrated  with  pure  potassium  hydrogen  tartrate, 
using  exactly  the  same  kind  of  litmus-paper  that  is  used  in  the  assay. 

Calcium  Tartrate  Assay. — The  following  method  was  adopted 


548  ACID    DERIVATIVES    OF   ALCOHOLS. 

at  the  Seventh  International  Congress  of  Applied  Chemistry  (London, 


6  grm.  are  always  to  be  taken  and  the  potassium  carbonate  solution 
is  added  to  the  100  c.c.  of  the  hydrochloric  acid  solution,  drop  by  drop 
by  means  of  a  pipette,  at  such  rate  as  to  require  in  all  about  five 
minutes.  The  mixture  is  boiled  for  20  minutes  longer  as  directed 
above.  The  modified  procedure  is  to  avoid  the  occlusion  of  calcium 
tartrate  in  the  calcium  carbonate. 

For  the  estimation  of  calcium  carbonate  in  calcium  tartrate,  the 
carbon  dioxide  that  the  sample  will  yield  must  be  weighed  directly. 

Commercial  Cream  of  Tartar.  —  Allen  suggested  (/.  Soc.  Chem. 
Ind.,  1896,  15,  681)  the  following  methods: 

1.  Dissolve  i.  88  1  grm.  of  the  sample,  free  from  moisture,  in  hot 
water  and  titrate  with  N/io  alkali,  phenolphthalein  being  used  as  an 
indicator.     In  the  absence  of  acid   potassium   sulphate   and  tartaric 
acid,  each  c.c.  of  alkali  represents  i%  of  acid  potassium  tartrate. 

2.  Ignite    i.  88  1  grm.  for  10  minutes,  boil  with  water,  filter  and 
wash  the  residue. 

a.  Titrate  the  filtrate  with  N/io  hydrochloric  acid  and  methyl- 
orange.     With  pure  tartar,  the  quantity  of  acid  used  will  equal  that 
consumed  in  the  previous  titration  with  alkali.     Each  c.c.  of  the  de- 
ficiency of  acid  is  equivalent  to  0.36%  of  calcium  sulphate,  or  0.72% 
of  potassium  hydrogen  sulphate.     Any  excess  of  acid  added  points  to 
the  presence  of  potassium  tartrate,  each  c.c.  representing  0.6%  thereof. 
If  the  titrated  liquid  be  treated  with  barium  chloride,  the  barium  sul- 
phate will  be  a  measure  of  the  calcium  sulphate  or  potassium  sulphate 
present. 

b.  The   carbonaceous   residue   is   ignited,   dissolved   in    20   c.c.   of 
N/io  acid,  filtered  from  any  insoluble  residue,  and  the  filtrate  titrated 
with  N/io  alkali.     Each  c.c.  corresponds  to  0.50%  of  calcium  tartrate 
or  0.36%  of  calcium  sulphate  (anhydrous). 

The  following  processes,  described  by  Rasch,  are  included  in 
Lunge's  Chemische-Technische  Unters.  Methoden,  being  for  analy- 
sis required  in  the  routine  of  tartar  works.  The  potassium  carbonate 
solution  directed  contains  5  grm.  of  the  pure  salt  in  100  c.c.  of  solu- 
tion. Phenolphthalein  is  used  as  indicator  and  N/io  potassium 
hydroxide  for  titration. 

ll  am  indebted  to  Mr.  W.  A.  Davis  for  a  special  communication  advising  me  of  this 
process.  —  H.  L. 


TARTARIC    ACID.  549 

Tartaric  Liquors. — 10  c.c.  are  boiled  with  40  c.c.  of  the  potassium 
carbonate  solution  for  a  short  time,  made  up  to  200  c.c.,  filtered 
through  a  dry  filter,  10  c.c.  of  the  filtrate  mixed  with  3  c.c.  of  glacial 
acetic  acid  and  100  c.c.  of  alcohol  and  the  precipitate  titrated.  The 
number  of  c.c.  used  multiplied  by  30  will  give  grm.  of  tartaric  acid 
yield  per  1000  c.c.  of  liquor. 

Old  Mother-liquors. — 10  c.c.  of  this  are  mixed  with  60  c.c.  of 
potassium  carbonate  solution,  boiled,  cooled,  made  up  to  200  c.c., 
filtered  through  a  dry  filter,  20  c.c.  of  the  filtrate  mixed  with  5  c.c.  of 
glacial  acetic  acid  and  100  c.c.  of  alcohol  and  the  precipitate  titrated. 
The  c.c.  used  multiplied  by  15  will  give  grm.  of  tartaric  acid  per  1000 
c.c.  of  liquor. 

Residuums. — 300  grm.  are  dissolved  in  a  porcelain  basin  with  25  c.c. 
of  hydrochloric  acid  (sp.  gr.  i.i)  and  500  c.c.  of  water,  the  mixture 
being  heated  to  boiling  with  constant  stirring.  A  portion  of  the  liquid 
is  filtered,  50  c.c.  of  the  filtrate  mixed  with  5  c.c.  of  glacial  acetic  acid 
and  130  c.c.  of  alcohol.  The  precipitate  is  titrated.  Each  5  c.c. 
of  this  required  will  be  approximately  equal  to  0.1%  of  tartaric  acid 
in  the  material. 

Mother-liquor  from  Calcium  Tartrate  Precipitates. — 200  c.c.  are 
evaporated  to  50  c.c.,  boiled  for  a  few  minutes  with  10  c.c.  of  the 
potassium  carbonate  solution,  made  up  to  100  c.c.,  filtered  through 
a  dry  filter,  60  c.c.  of  the  filtrate  mixed  in  a  measuring  flask  with  10  c.c. 
of  hydrochloric  acid  (sp.  gr.  i.i)  and  alcohol  added  to  make  a  volume 
of  1 80  c.c.  The  mixture  is  shaken,  filtered  promptly  through  a  dry 
filter,  and  the  following  are  added  in  succession  to  150  c.c.  of  the 
filtrate.  Ten  c.c.  potassium  carbonate  solution,  5  c.c.  glacial  acetic 
acid,  and  100  c.c.  of  alcohol.  The  mixture  is  well  shaken  and  allowed 
to  stand  for  twenty-four  hours. 

The  precipitate  is  titrated.  Each  10  c.c.  used  will  be  equivalent  to 
1.5  grm.  tartaric  acid  in  1000  c.c.  of  the  liquor. 

Free  Sulphuric  Acid  in  Liquors. — 20  c.c.  of  the  liquor  are  made 
up  to  200  c.c.  with  alcohol,  allowed  to  stand  overnight,  filtered 
through  a  dry  filter,  100  c.c.  of  the  filtrate  cleared  of  alcohol  and 
precipitated  with  barium  chloride  as  usual. 

Detection  of  Lead. — The  following  process  is  from  a  description 
furnished  by  W.  A.  Davis,  but  this  has  been  modified  by  a  further 
communication,  for  abstract  of  which,  see  Appendix,  page  569 


55°  ACID    DERIVATIVES    OF   ALCOHOLS. 

10  grm.  of  tartaric  acid  are  dissolved  in  about  20  c.c.  of  distilled 
water,  the  solution  filtered  if  necessary  and  placed  in  a  tall,  narrow 
cylinder  of  colourless  glass  marked  at  100  c.c.  Solution  of  hydrogen 
sulphide  (made  by  passing  the  gas  through  water  for  at  least  two 
hours  before  using)  is  added  in  amount  sufficient  to  make  100  c.c. 
and  after  10  minutes  the  color  of  the  solution  is  noted.  If  no  colour 
is  produced  lead  is  absent,  or  at  least  below  0.0005%.  This  is  the 
case  with  the  best  product. 

A  slight  bluish  turbidity  represents  about  0.00075  %• 

A  decided  blue-yellow  or  gray  represents  o.ooi  %. 

A  brown  tint  may  be  due  to  either  iron  or  lead,  but  the  latter  is 
usually  distinguished  by  the  blacker  tint  seen  when  the  liquid  is  held 
against  a  white  background. 

10  grm.  of  cream  of  tartar  are  heated  with  about  50  c.c.  of  water, 
and  ammonia  added  until  all  the  potassium  hydrogen  tartrate  is 
dissolved.  It  the  solution  is  coloured  it  must  be  treated  with  purified 
animal  charcoal  and  filtered.  The  liquid  is  diluted  to  100  c.c.,  as 
above  noted,  and  3  drops  of  ammonium  sulphide  added.  If  the 
reagent  is  yellow,  allowance  must  be  made  for  this  tint. 

If  no  colouration  is  produced  by  the  reagent,  lead  is  below  0.0005%. 

A  slight  brownish-yellow  shows  about  0.00075  %. 

A  clear  brown  tint,  about  straw  coloured,  shows  about  0.001%. 

Copper  is  shown  by  the  blue  tint  imparted  to  the  ammonia  solution 
before  the  sulphide  is  added;  iron  shows  a  dark  green  precipitate 
or  a  green  tint.  These  tints  mask  the  lead  reaction  and  in  such 
cases  a  few  drops  of  potassium  cyanide  solution  must  be  added 
to  the  alkaline  solution  before  filtering,  and  the  above  procedure 
followed. 

For  the  separation  of  ordinary  tartaric  acid,  mesotartaric  acid,  and 
the  racemic  association  of  two  active  forms,  Hollemann  (Rec.  Trav. 
Chim.j  1898,  17,  66)  devised  the  following  method:  The  aqueous 
solution  of  the  free  acid  is  evaporated  in  the  water-bath  until  crystal- 
lisation begins,  and  the  liquid  is  allowed  to  stand  in  a  cool  place  for  24 
hours.  Racemic  acid  separates  and  the  crystals  may  be  carefully 
drained,  dried,  and  weighed.  The  mother  liquor  is  diluted  to  20  c.c.; 
one-half  of  this  exactly  neutralised  by  potassium  hydroxide,  the  other 
half  added,  and  the  mixture  allowed  to  stand  overnight.  Potassium 
hydrogen  tartrate  separates  quantitively,  and  can  be  collected,  dried, 
and  weighed.  The  filtrate  is  treated  with  ammonia,  then  slightly 


TARTARIC   ACID.  551 

acidified  with  acetic  acid,  boiled,  and  calcium  chloride  solution  added. 
The  calcium  mesotartrate  is  thrown  down. 

Detection  of  Yeasts  in  Lees. — Rasch  states  (Lunge  9Chem.  Tech.  Unters. 
Meth.,  vol.  3)  that  it  is  sometimes  advisable  to  ascertain  if  lees  have 
an  excessive  amount  of  yeast  cells,  and  recommends  the  following: 
40  grm.  of  the  sample  are  stirred  with  some  water  in  a  400  c.c.  beaker, 
50  c.c.  of  10%  calcium  chloride  solution  added,  the  solution  neutral- 
ised accurately  with  milk  of  lime,  the  beaker  filled  with  water,  and 
the  mixture  kept  at  35°  for  24  hours.  Good,  well-dried  lees  will  not 
show  appreciable  fermentation. 

Tartrates. — Tartaric  acid  contains  4  atoms  of  replaceable  hydro- 
gen but  only  2  of  these  are  in  the  true  acid-forming  position,  hence 
the  acid  is  bibasic  and  with  members  of  the  potassium  group  forms 
2  series  of  salts,  tartrates  and  hydrogen  tartrates,  the  latter  being  often 
erroneously  called  "bitartrates."  Few  of  the  salts  are  soluble  in  water, 
and  all  are  insoluble  in  alcohol.  The  salts  of  the  members  of  the 
potassium  group  unite  readily  with  those  of  some  of  the  other  groups 
to  form  double  tartrates  which  are  not  decomposed  on  adding  strong 
hydroxides.  In  this  way,  the  addition  of  sodium  potassium  tartrate 
to  copper  sulphate  solution  will  prevent  entirely  the  precipitation  of 
copper  hydroxide  on  adding  sodium  hydroxide.  This  mixture  is 
known  as  Fehling's  solution.  The  analysis  of  these  double  tartrates 
is  described  on  page  538. 

Potassium  Tartrates. 

The  most  important  of  these  salts  is  the  potassium  hydrogen 
tartrate,  often  erroneously  called  bitartrate.  This  is  the  principal 
constituent  of  tartar,  argol,  and  wine-lees,  and  is  of  importance  in  the 
pure  state  as  a  source  of  tartaric  acid  and  as  a  form  for  the  determina- 
tion of  that  body. 

Pure  potassium  hydrogen  tartrate  may  be  conveniently  prepared  by 
dividing  a  solution  of  tartaric  acid  into  two  equal  parts,  neutralising 
one  portion  with  potassium  carbonate,  and  adding  the  other.  The 
product  may  be  purified  by  recrystallisation  from  hot  water. 

It  forms  colourless  crystals,  is  soluble  in  240  parts  of  water  at  10°, 
180  at  20°,  and  in  about  15  parts  of  boiling  water.  In  alcohol  it  is 
much  less  soluble.  It  requires  (at  15°)  400  parts  of  a  liquid  con- 
taining 10.5%  of  alcohol,  and  for  50%  alcohol  about  2,000  parts  for 
solution.  In  still  stronger  spirit  it  is  practically  insoluble.  The  presence 
of  glucose  does  not  affect  its  solubility  in  water  or  weak  alcohol;  but 


552 


ACID    DERIVATIVES    OF   ALCOHOLS. 


some  salts  and  acids  have  great  influence.  This  shown  by  the  follow- 
ing table  by  Warington,  in  which  the  effect  of  water  containing 
equivalent  quantities  of  acids  is  given.  For  comparison  with  them, 
experiments  were  also  made  with  solutions  containing  equivalent 
amounts  of  acetic  and  citric  acids  neutralised  by  potassium  hydroxide. 
All  the  experiments  were  made  at  14°: 


Solvent 

Grm.  of  acid  or 
t,alt  in  100  c.c.  of 
Solvent 

Grm.  of  tartrate 
dissolved  by  100 
c.c.  of  solvent 

Water          

4.22 

Acetic  acid  

8106 

422 

Tartaric  acid  

I    O33I 

•322 

Citric  acid  

8448 

.j^ji 

^4O 

Sulphuric  acid  

68?  7 

I    7OI 

Hydrochloric  acid  

^O37 

I    040 

Nitric  acid  

844  s 

I    060 

Potassium  acetate 

i    387? 

744 

Potassium  citrate 

I   3066 

842 

These  results  are  of  importance  in  the  estimation  of  tartaric  acid  as 
potassium  hydrogen  tartrate.  Mineral  acids  should  not  be  present  nor 
any  large  excess  of  potassium  acetate  or  citrate.  On  the  other  hand, 
solutions  of  potassium  sulphate,  nitrate  and,  especially,  chloride 
have  very  little  solvent  action  on  the  precipitated  tartrate.  Thus  the 
solubility  of  the  potassium  hydrogen  tartrate  at  12°  is  i  part  in  3213 
of  a  5%  solution  of  potassium  chloride,  and  only  i  in  4401  of  a  10% 
solution  of  the  same  salt. 

Potassium  hydrogen  tartrate  dissolves  many  oxides,  forming  double 
tartrates;  tartar  emetic  is  a  compound  of  this  character. 

Cream  of  tartar  consists  chiefly  of  potassium  hydrogen  tartrate.  Its 
composition  and  the  mode  of  assaying  it  are  considered  on  page  548. 

When  potassium  hydrogen  tartrate  is  treated  with  solution  of 
potassium  carbonate  or  hydroxide  until  the  liquid  ceases  to  redden 
litmus-paper,  there  results: 

Potassium  tartrate ;  neutral  potassium  tartrate.  This  forms  colour- 
less crystals  freely  soluble.  When  its  solution  is  treated  with  an  acid, 
the  hydrogen  tartrate  is  precipitated. 

Potassium  sodium  tartrate,  Rochelle  salt  is  produced  by  neu- 
tralising cream  of  tartar  with  sodium  hydroxide  or  sodium  carbonate. 


TARTRATES.  553 

It  forms  large  crystals,  containing  4  mol.  of  water,  and  is  very  readily 
soluble.  Addition  of  acetic  acid  precipitates  crystalline  potassium 
liydrogen  tartrate.  This  reaction  distinguishes  it  from  the  sodium 
tartrate. 

Seidlitz  powders  contain  potassium  sodium  tartrate.  Sometimes 
the  tartrate  is  largely,  and  occasionally  entirely,  replaced  by  sodium  hy- 
drogen carbonate.  Such  a  preparation  would  be  strongly  alkaline,  and 
notably  different  from  Seidlitz  powder.  On  the  other  hand,  if  the  acid 
is  in  excess,  the  powder  is  apt  to  produce  a  turbid  solution  with 
water,  owing  to  formation  of  potassium  hydrogen  tartrate. 

In  examining  Seidlitz  powders,  the  absence  of  notable  proportions 
of  sulphates  should  be  proved,  as  a  substitution  of  potassium  hydrogen 
sulphate  for  tartaric  acid  is  not  unlikely.  Some  powders  receive  an 
addition  of  magnesium  sulphate,  or  a  minute  quantity  (i/ioo  grain) 
of  tartar  emetic,  while  others  are  flavoured  with  lemon  or  ginger,  and 
sweetened  with  sugar.  Potassium  chlorate  is  a  constituent  of  some 
proprietory  remedies  of  the  nature  of  Seidlitz  powders. 

Potassium  Ferric  Tartrate. — Prepared  by  adding  precipitated 
ferric  hydroxide  to  acid  potassium  tartrate  and  treating  with  cold 
water.  It  constitutes  the  jerrum  tartaratum  of  pharmacy.  The  solu- 
tion acidulated  with  hydrochloric  acid  should  give  a  copious  blue 
precipitate  with  the  ferrocyanides  but  none  with  the  ferricyanides. 
It  should  yield  30%  of  Fe2O3,  as  estimated  from  the  weight  of  the  ash 
insoluble  in  water. 

Potassium  Antimonyl  Tartrate. — Tartarised  antimony;  tartar 
emetic.  This  is  prepared  by  mixing  antimonious  oxide  with  potassium 
hydrogen  tartrate,  and  subsequently  adding  water,  boiling,  filtering 
and  crystallising.  Cold  water  dissolves  7%,  and  boiling  water  53% 
of  the  salt;  the  solution  has  an  acid  reaction.  Anlimonial  wine  is  a 
solution  of  tartar  emetic  in  wine. 

Tartar  emetic  is  now  extensively  employed  for  fixing  certain  coal- 
tar  colours  on  cotton,  its  value  for  this  purpose  depending  on  the  content 
of  antimony.  It  is  frequently  largely  adulterated,  the  percentage  of 
antimony  being  sometimes  scarcely  one-half  of  that  present  in  the  pure 
substance. 

The  antimony  may  be  conveniently  estimated  volumetrically,  in  a 
manner  described  by  W.  B.  Hart  (/.  Soc.  Chem.  Ind.,  1884,  3, 
294).  The  sample  is  dissolved  in  water  and  acid  sodium  carbonate 
.added  to  the  solution.  Excess  of  a  standard  solution  of  calcium 


554  ACID    DERIVATIVES    OF   ALCOHOLS. 

hypochlorite  is  then  added.  The  excess  is  found  by  titrating  back  with 
a  N/io  solution  of  sodium  arsenite  until  a  drop  of  the  liquid  ceases 
to  give  a  blue  with  potassium  iodide  and  starch.  The  strength  of 
the  hypochlorite  solution  is  found  by  taking  a  measure  equal  to  that 
added  to  the  antimony  solution  and  titrating  with  arsenite  as  before, 
i  c.c.  of  a  solution  prepared  with  4.95  grm.  of  pure  arsenous  oxide 
per  litre  has  the  same  reducing  power  as  0.0060  grm.  of  antimony  or 
0.0072  of  antimonous  oxide. 

Potassium  antimonyl  oxalate,  has  been  used  as  an  adulterant 
of,  and  substitute  for,  tartar-emetic.  It  is  readly  soluble,  does  not 
blacken  on  ignition  or  on  heating  with  sulphuric  acid,  and  gives  a 
white  precipitate  on  adding  calcium  chloride  to  the  solution  previously 
acidified  with  acetic  acid.  The  salt  yields  only  23.7%  of  antimonous 
oxide. 

Ammonium  tartrates  closely  resemble  the  corresponding  potas- 
sium salts,  but  are  wholly  volatile  on  ignition. 

Calcium  tartrate,  is  a  natural  constituent  of  tartar  from  wine,  the 
proportion  contained  being  much  increased  if  the  wine  has  been 
"plastered."  It  also  constitutes  the  greater  part  of  the  residue  ob- 
tained on  treating  commercial  tartars  with  hot  water.  Calcium 
tartrate  is  precipitated  as  a  crystalline  powder  containing  4  mol.  of 
water  by  adding  excess  of  calcium  chloride  to  a  solution  of  a  tartrate. 
It  is  soluble  in  6265  parts  of  water  at  15°  and  in  352  parts  of  boiling 
water.  Strong  acids  and  potassium  hydrogen  tartrate  dissolve  it 
readily;  and  hence  it  is  frequently  present  in  notable  quantity  even 
in  purified  tartars.  These  solutions  are  precipitated  by  ammonium 
hydroxide,  either  immediately  or  after  some  time.  Calcium  tartrate  is 
soluble  in  ammonium  chloride  and  in-  cold  alkali,  the  latter  solution 
being  reprecipitated  on  boiling.  By  digestion  with  a  hot  neutral  solu- 
tion of  copper  chloride  it  is  converted  into  insoluble  copper  tartrate. 
This  reaction  distinguishes  it  from  calcium  citrate,  but  the  reaction 
fails  with  mixtures  containing  a  large  proportion  of  citrate.  The 
tartrate  differs  from  the  racemate  and  oxalate  by  its  solubility  in 
acetic  acid.  (For  assay  of  crude  calcium  tartrate  see  p.  547.) 

Calcium  racemate,  is  even  less  soluble  in  water  than  calcium  tar- 
trate, and  is  precipitated  in  fine  needles  on  adding  calcium  sulphate  to 
a  soluble  racemate  or  even  to  a  solution  of  free  racemic  acid.  Calcium 
racemate  resembles  the  oxalate  in  being  insoluble  in  acetic  acid.  It 
dissolves  in  hydrochloric  acid  to  form  a  solution  which  is  at  once  pre- 


CITRIC    ACID.  555 

cipitated  on  adding  ammonium  hydroxide,  whilst  the  tartrate  is  not 
precipitated  for  some  time. 

Citric  Acid. 

Citric  acid  occurs  in  a  free  state  in  the  juices  of  many  plants  of  the 
genus  of  Citrus  (order,  Aurantiacea) ,  and  also  in  the  gooseberry,  cran- 
berry, currant,  tamarind  and  many  other  fruits.  The  lemon,  lime 
and  bergamot  are  the  fruits  from  which  it  is  extracted.  It  has  also 
been  manufactured  from  unripe  gooseberries,  which  yield  about  i% 
of  their  weight  of  citric  acid,  besides  containing  malic  acid.  Good 
lemons  yield  about  5.5  %  of  crystallised  citric  acid.  Calcium  and 
potassium  citrates  are  also  widely  distributed  in  the  vegetable 
kingdom. 

Citric  acid  is  prepared  from  lime,  lemon  or  bergamot  juice,  by 
neutralising  the  liquid  with  calcium  carbonate,  decomposing  the 
resultant  calcium  citrate  by  an  equivalent  amount  of  sulphuric  acid, 
and  evaporating  the  liquid  to  the  crystallising  point. 

Citric  acid  usually  occurs  as  a  crystalline  powder  or  in  transparent 
colourless  prisms.  In  the  trade,  the  crystals  are  assumed  to  have  the 
composition  C6H8O7-f  H2O. 

Crystallised  citric  acid  begins  to  lose  water  at  75°,  becomes  anhy- 
drous at  135°,  fuses  at  153°,  and  at  about  175°  decomposes  into  water 
and  aconitic  acid,  C6H^36. 

Citric  acid  has  a  strong  acid  taste,  is  soluble  in  about  half  its 
weight  of  water  at  25°  and  0.4  part  of  boiling  water,  in  1.5  parts  of 
strong  alcohol  at  25°  and  1.4  of  boiling  alcohol  and  in  18  parts  of 
ether.  The  solution  has  no  optical  activity.  Aqueous  solutions 
readily  mold. 

Citric  acid  is  very  soluble  in  dilute  and  absolute  alcohol,  but  is 
nearly  insoluble  in  ether,  chloroform,  benzene  or  petroleum  spirit. 

Detection  and  Estimation  of  Citric  Acid  and  Citrates.— 
When  5  grm.  of  citric  acid  are  heated  with  30  c.c.  of  ammonium  hy- 
droxide for  6  hours  in  a  sealed  tube  at  a  temperature  of  120°,  a  yellow 
colouration  is  observed  and  small  crystals  are  formed.  If  the  cooled 
liquid  be  poured  into  an  evaporating  basin,  it  becomes  blue  in  the 
course  of  some  hours,  the  colour  becoming  more  intense  on  standing,  and 
in  a  few  days  turning  to  green,  and  ultimately  disappearing.  The 
change  of  colour  goes  on  more  slowly  in  the  dark.  Heating  the  liquid 
on  the  water-bath  hastens  the  production  of  the  colour.  Malic,  tartaric, 
and  oxalic  acids  do  not  interfere,  even  when  present  in  large  excess,  but 


556  ACID    DERIVATIVES    OF   ALCOHOLS. 

itaconic  acid  must  be  absent.  It  is  said  that  o.oi  grm.  of  citric  acid 
can  be  detected  by  this  process  (Zeits.  Anal.  Chem.,  1878,  17,  73). 

Calcium  citrate  is  very  sparingly  soluble,  and  less  soluble  in  hot 
water  than  in  cold.  Hence,  addition  of  excess  of  lime-water  to  a 
solution  of  citric  acid  produces  but  a  slight  precipitate  in  the  cold, 
but  a  somewhat  more  considerable  precipitate  of  calcium  citrate  is 
obtained  on  boiling,  the  deposit  redissolving  as  the  solution  cools. 

Precipitation  as  calcium  citrate  may  be  employed  for  the  estima- 
tion of  citric  acid,  and  serves  to  separate  citrates  from  malates,  ace- 
tates, formates  and  butyrates;  but  the  precipitate  may  contain  calcium 
tartrate,  oxalate  or  racemate. 

Citric  acid  may  be  roughly  separated  from  tartaric  acid  by  digesting 
the  mixed  calcium  salts  with  a  hot  and  perfectly  neutral  solution 
of  copper  chloride,  when  soluble  copper  citrate  is  formed  and  an  insol- 
uble tartrate  remains.  In  the  case  of  mixed  tartrates  and  citrates 
which  can  be  converted  into  the  calcium  salts  by  precipitation  with 
calcium  chloride  or  nitrate  in  perfectly  neutral  boiling  solution,  this 
method  of  separation  is  occasionally  convenient  for  qualitative  pur- 
poses, but  it  is  greatly  inferior  to  the  precipitation  of  the  tartaric  acid 
as  potassium  hydrogen  tartrate,  and  fails  wholly  if  the  proportion  of 
tartrate  is  small. 

From  tartaric  acid,  citric  acid  is  best  separated  by  the  method  de- 
scribed on  page  558.  In  the  nitrate  from  the  precipitate  of  potassium 
hydrogen  tartrate  the  citric  acid  may  be  determined  by  boiling  off  the 
lacohol,  exactly  neutralising  with  sodium  hydroxide,  and  proceeding  as 
directed  on  page  561,  or  by  precipitation  with  barium  acetate  or 
lead  acetate.  If  the  acids  do  not  exist  in  the  free  state,  the  solution 
must  be  prepared  as  directed  under  Tartaric  Acid. 

From  oxalic  acid  citric  acid  is  separated  by  neutralising  the  solution 
with  sodium  hydroxide,  acidifying  with  acetic  acid  and  adding  calcium 
sulphate  or  chloride.  After  filtering  from  the  precipitated  calcium 
oxalate,  the  citric  acid  may  be  thrown  down  by  adding  lime-water  and 
boiling. 

If  moderately  pure,  citric  acid  may  sometimes  be  conveniently  con- 
verted into  barium  citrate  by  precipitating  the  neutralised  solution 
with  barium  acetate  and  adding  2  volumes  of  95%  alcohol.  After 
24  hours,  the  precipitate  is  filtered  off,  washed  with  alcohol  of  63%, 
ignited,  moistened  with  sulphuric  acid,  again  ignited,  and  the  weight 
multiplied  by  0.601.  Alkaline  acetates  do  not  interfere,  so  that  the 


CITRIC   ACID.  557 

method  is  applicable  to  liquids  from  which  the  tartaric  acid  has  been 
separated  as  potassium  hydrogen  tartrate. 

In  the  absence  of  other  acids,  citric  acid  may  be  titrated  with 
standard  alkali,  neutral  litmus-paper  being  used.  The  alkali  should 
be  set  against  pure  citric  acid. 

For  the  estimation  of  citric  acid  in  presence  of  heavy  metals,  the 
latter  should  be  first  removed  by  hydrogen  sulphide  or  sodium  sulphide 
and  the  filtered  liquid  rendered  neutral  and  precipitated  with  excess 
of  lead  acetate.  The  unfiltered  liquid  is  mixed  with  an  equal  volume 
of  alcohol,  filtered,  the  precipitate  washed  with  proof  spirit  and  treated 
with  ammonium  hydroxide.  The  filtrate  may  contain  citric  and  tar- 
taric acids,  but  will  be  free  from  sulphates,  phosphates  and  oxalates. 
When  unmixed  with  other  lead  salts,  lead  citrate  may  be  suspended 
in  water,  decomposed  by  hydrogen  sulphide,  the  liquid  filtered,  well 
boiled  and  the  citric  acid  in  the  solution  titrated  with  alkali. 

Full  descriptions  of  the  methods  of  determining  citric  acid  in  juices 
and  citric  acid  liquors,  will  be  found  in  subsequent  paragraphs. 

Commercial  citric  acid  frequently  contains  small  quantities  of 
calcium  salts,  due  to  imperfect  manufacture,  and  traces  of  iron,  lead 
and  copper  are  also  met  with — these  last  being  derived  from  the 
vessels  used  for  the  crystallisation  and  evaporation  of  the  acid  liquids. 

The  presence  of  all  these  impurities  is  indicated  by  igniting  5  or 
10  grms  of  the  sample  in  a  porcelain  crucible.  The  ash  usually  ranges 
from  0.05  to  0.25%.  When  the  ash  does  not  exceed  the  latter  amount, 
it  is  rarely  of  importance  to  examine  it  further,  except  for  poisonous 
metals. 

For  the  detection  of  lead  the  procedure  is  the  same  as  with  tartaric 
acid  (p.  550).  See  also  appendix,  page  569; 

A  colourless  solution  shows  below  0.0003  %• 

Faint  blue         "  "         "  0.00075%. 

Decided  blue  yellow       "         "  o.ooi  %. 

The  presence  of  poisonous  metals  in  citric  acid  is  accidental,  and 
the  proportion  present  is  usually  small  (i  part  in  10,000);  but  as  lead 
and  copper  are  occasionally  present  in  dangerous  amount,  it  is 
necessary  to  take  every  precaution  to  avoid  their  introduction. 

If  samples  of  citric  acid  contain  sulplmric  acid,  they  will  be 
deliquescent.  Sulphuric  acid  and  sulphates  may  be  detected  and 
determined  by  acidifying  rather  strongly  with  hydrochloric  acid  and 


55°  ACID    DERIVATIVES    OF    ALCOHOLS. 

adding  barium  chloride.  233  parts  of  the  precipitate  correspond  to 
98  of  sulphuric  acid. 

Formerly  citric  acid  was  liable  to  adulteration  with  tartaric  acid. 
If  present,  tartaric  acid  may  be  conveniently  detected  by  the  charring 
which  occurs  on  heating  the  sample  with  concentrated  sulphuric  acid, 
as  described  on  page  538.  When  the  proportion  of  tartaric  acid  in  ad- 
mixture with  the  citric  acid  is  not  too  small,  it  may  be  detected  by  the 
dark  mixture  produced,  within  5  minutes,  when  i  grm.  of  the  sample  is 
dissolved  in  10  c.c.  of  a  cold  saturated  solution  of  potassium  dichromate. 

For  the  detection  of  tartaric  acid  in  citric  acid,  Vulpius  dissolves 
0.5  grm.  of  the  sample  in  10  c.c.  of  distilled  water,  and  adds  5  drops 
of  the  solution,  drop  by  drop,  to  15  c.c.  of  lime-water.  If  the  citric 
acid  contain  mere  traces  of  tartaric  acid,  a  distinct  turbidity  will  be 
produced  in  a  few  moments,  which  increases  on  adding  more  of  the 
acid  solution  and  stirring.  In  this  manner  i%  of  tartaric  acid  may  be 
detected. 

If  present  in  admixture  with  citric  acid,  tartaric  acid  is  best  estimated 
by  the  methods  on  pp.  545  to  548. 

Citric  Acid  Liquors. — This  term  is  applied  to  the  liquors  resulting 
in  citric  acid  works  from  the  treatment  of  the  calcium  citrate  with 
sulphuric  acid.  The  assay  is  limited  to  the  estimation  of  citric  and 
sulphuric  acids.  For  this  purpose  the  total  acidity  may  be  deter- 
mined by  titration  with  standard  alkali  and  phenolphthalein,  and  the 
sulphuric  acid  then  determined.  By  subtracting  the  acidity  due  to  the 
latter  from  the  total  found  by  titration,  that  due  to  the  citric  acid  alone 
is  ascertained.  The  free  sulphuric  acid  is  ascertained  by  treating  10  or 
20  c.c.  of  the  liquor  with  5  times  its  volume  of  strong  alcohol.  After 
twelve  hours  a  portion  of  the  clear  liquor  is  treated  with  more  alcohol, 
and,  if  opalescence  result,  the  whole  is  treated  in  the  same  way.  The 
liquid  is  ultimately  filtered,  the  precipitated  sulphates  washed  with  spirit 
and  the  filtrate  precipitated  with  an  alcoholic  solution  of  calcium  chlo- 
ride. The  precipitated  calcium  sulphate  is  allowed  to  settle  completely, 
the  supernatant  liquor  poured  off,  and  the  precipitate  and  small  quan- 
tity of  remaining  liquor  gently  warmed.  The  alcohol  is  gradually  dis- 
placed by  cautious  additions  of  small  quantities  of  water,  and,  when  the 
precipitate  has  become  crystalline,  alcohol  is  added,  and  the  precipitate 
collected  on  a  filter,  washed  with  alcohol,  ignited,  and  weighed  as 
calcium  sulphate.  The  weight  multiplied  by  0.7206  gives  the  sul- 
phuric acid  (H2SO4)  in  the  liquor  taken. 


CITRIC   ACID.  559 

Another  method,  which  agrees  well  with  the  above  is  to  neutralise 
exactly  a  known  measure  of  the  citric  liquor  with  pure  sodium  hydroxide 
evaporate  to  dryness,  and  ignite  gently  in  platinum.  The  ash  is  wholly 
dissolved  in  a  known  quantity  of  standard  acid,  and  the  excess  of  acid 
ascertained  by  titration  with  alkali.  (In  presence  of  iron  or  aluminum, 
sodium  tartrate  or  sodium  potassium  tartrate  should  be  added  before 
titration.)  The  acid  neutralised  by  the  ash  is  equivalent  to  the  organic 
acid  contained  in  the  liquor  used. 

In  old  liquor,  the  citric  acid  should  be  precipitated  as  calcium 
salt,  as  other  organic  acids  will  be  present  in  considerable  amount. 
For  this  purpose  the  liquor  is  treated  exactly  as  directed  for 
juice. 

Lemon  Juice;  Bergamot  Juice;  Lime  Juice.— These  juices  con- 
tain citric  acid;  acids  other  than  citric;  citrates;  salts  of  organic  acids 
other  than  citric;  salts  of  inorganic  acids;  and  albuminous,  mucilag- 
inous, saccharine  and  indifferent  bodies.  Alcohol  is  frequently 
added  as  a  preservative,  and  mineral  acids  are  not  uncommonly 
employed  as  adulterants.  Verjuice  has  also  been  used  for  the 
purpose. 

J.  Macagno  finds  that  the  alcoholic  fermentation  which  takes  place 
when  freshly  expressed  lemon-juice  is  kept  does  not  diminish  the 
amount  of  citric  acid  present,  but  that  this  is  succeeded  by  another 
fermentation  which  diminishes  the  citric  acid  and  other  organic  acids 
(chiefly  acetic  and  propionic)  increase.  Similarly,  juice  expressed  from 
rotten  fruit  contains  acids  other  than  citric,  sometimes  to  the  extent 
of  10%. 

Citric  acid  juices  lose  some  of  their  acidity  by  concentration.  War- 
ington  observed  a  loss  of  3.5%  of  the  total  free  acid  on  concentrating 
English-pressed  juice  to  1/6  of  its  original  bulk.  The  loss  is  due,  at 
least  in  part,  to  the  presence  of  volatile  organic  acids,  which,  of  course, 
exist  in  much  smaller  amount  in  concentrated  juice.  Warington  found 
1.25%  of  the  total  acidity  of  concentrated  juice  to  be  due  to  volatile 
acids.  Among  the  latter  were  recognised  formic,  acetic  and  probably 
propionic  acids. 

The  following  table,  compiled  from  Warington's  data,  shows  the 
sp.  gr.  acid,  and  combined  organic  acid  (the  last  two  expressed  in 
terms  of  crystallised  citric  acid)  of  the  various  citric  juices  commonly 
met  with  in  commerce. 


560 


ACID    DERIVATIVES    OF   ALCOHOLS. 


Combined 

Specific 

Acid,  oz.  per 

organic  acid 

gravity 

gallon 

oz.  per 

gallon 

Lime  juice: 

Raw  Sicilian  

6-Q 

o  8s 

Raw  English  

i  .04  —i  05 

ii—  1  3 

o.  3 

Concentrated  

i  .  20  —  i  .  25 

* 

50—72 

6-8 

Bergamot  juice: 

Concentrated 

I    22    —I    2<t 

4.7—  re 

7-8 

Lemon  juice: 

Raw 

I    035—1    040 

10  6—13  c 

O  4.—  O    7 

Concentrated                 .  .          .        .    . 

I    28   -I    38 

82-112 

8-6 

In  the  following  table,  due  to  Grosjean,  are  given  determinations 
of  the  free  acid  and  precipitable  organic  acid  (both  calculated  as  citric 
acid)  in  commercial  samples  of  concentrated  lemon  and  other  juices: 


Specific 
gravity 

Acid  (reckoned  as 
citric  acid), 
oz.  per  gallon 

Proportion 
of 
precipitable 
to  100  of 
acid 

Acid 

Total  acid 
precipitable 

Lemon  juice: 
Average  of  65  samples  

i  .241 
i  .  240 
1-235 

1-235 
1-235 

i  .326 
i  .205 

i  .400 
1-350 

62.1 
65.8 
64.9 

47-9 
52-3 

108.3 
59-2 

16.8 
11.7 

61.6 

59-7 
55-7 

48.5 
49-9 

99.8 
53-9 

ii.  6 

8.0 

99-2 
90.7 
85.8 

101  .4 
95-4 

92.2 
91.1 

69.0 

Sample  A  

Sample  B  

Bergamot  juice: 
Highest 

Lowest                            

Lime  juice: 
Sample  A             

Sample  B           

Orange  juice: 
Sample  A  

Sample  B 

From  the  first  of  these  tables  it  will  be  seen  that  English-pressed 
juice  contains  more  free  and  less  combined  acid  than  the  raw  Italian 
and  Sicilian  juices.  This  is  probably  due  to  the  fact  that  the  finest  and 
ripest  fruit  is  sent  to  England,  while  the  windfalls  and  damaged  fruit 
are  treated  locally. 


CITRIC   ACID.  561 

Concentrated  bergamot  juice  is  far  less  acid  than  lemon  juice,  while 
concentrated  lime  juice  is  a  thick  viscid  fluid  far  exceeding  the  others 
both  in  density  and  acidity. 

The  assay  of  genuine  juice  is  practically  confined  to  the  esti- 
mation of  citric  acid  and  citrates,  and  for  this  purpose  the  following 
processes  are  employed: 

Specific  Gravity. — A  special  hydrometer  is  sometimes  used.  On 
this  "citrometer, "  60  degrees  correspond  to  a  sp.  gr.  of  1.240,  so  that 
each  degree  appears  to  be  equal  to  0.004  sp.  gr.  above  unity. 

The  valuation  by  sp.  gr.  is  open  to  many  frauds.  Bergamot  juice, 
which  has  a  high  gravity  but  low  acidity,  has  been  mixed  with  lemon 
juice,  and  sea- water  has  been  added  to  the  juice  during  concentration. 
Of  course,  the  presence  of  alcohol  materially  affects  the  density,  but 
it  may  be  got  rid  of  by  boiling  the  juice  and  again  taking  the  sp.  gr. 
after  making  up  the  volume  to  that  originally  employed. 

Estimation  of  the  Acid. — This  is  effected  by  titration  with  N/2 
sodium  hydroxide,  neutral  litmus-paper  being  used  as  an  indicator. 
In  the  case  of  concentrated  juice,  50  c.c.  should  be  diluted  to  500,  and 
25  c.c.  to  30  c.c.  of  the  diluted  liquid  employed  for  the  titration. 
With  unconcentrated  juice,  10  c.c.  or  20  c.c.  may  be  measured  out 
at  once.  In  either  case,  the  alkali  is  added  in  quantity  sufficient  to 
neutralise  about  80%  of  the  acid  present;  the  liquid  is  then  boiled 
for  a  few  minutes,  and  when  quite  cold  the  titration  is  completed. 
The  neutralising  power  of  the  alkali  should  be  known  in  terms  of 
pure  citric  acid. 

Estimation  of  the  Citrate  and  Other  Organic  Salts. — This 
is  effected  by  evaporating  to  dryness  the  portion  of  juice  which  has 
been  already  neutralised  for  the  determination  of  free  acid.  The  resi- 
due left  on  evaporation  is  heated  gradually,  and  charred  at  a  low 
red  heat.  The  ignited  mass  is  treated  with  water,  a  known  volume 
of  standard  sulphuric  acid  added,  the  liquid  boiled  and  filtered,  and 
the  excess  of  acid  ascertained  in  the  filtrate  by  standard  alkali.  The 
amount  of  sulphuric  acid  neutralised  by  the  ash  is  equivalent  to  the 
total  organic  acid  of  the  sample,  for  on  ignition  all  the  salts  of 
organic  acids  were  converted  into  the  corresponding  carbonates.  49 
parts  of  sulphuric  acid  neutralised  =  40  of  sodium  hydroxide  =  70  of 
H3C6H5O7,H2O,  or  67  of  2H3C6HSO7,H2O. 

The  result  gives  the  total  organic  acid  of  the  juice  taken,  calculated 
as  citric  acid.  By  subtracting  the  amount  of  free  citric  acid,  obtained 
VOL.  1—36 


562  ACID    DERIVATIVES    OF    ALCOHOLS. 

by  titration  of  the  acid  juice,  the  amount  of  combined  citric  acid 
is  ascertained. 

If  the  original  acid  juice  is  evaporated  and  ignited,  and  the  combined 
citric  acid  calculated  from  the  neutralising  power  of  the  ash,  the  results 
obtained  are  too  high,  owing  to  the  decompositions  by  the  citric  acid 
during  evaporation. 

Estimation  of  the  Real  Citric  Acid. — Of  the  organic  acids  pres- 
ent in  genuine  lemon  and  similar  juices,  the  citric  is  the  only  one  of 
importance  which  forms  an  approximately  insoluble  calcium  salt. 
Calcium  malate  and  aconitate  are  pretty  freely  soluble,  and  the  same 
remark  applies  more  strongly  to  calcium  acetate  and  butyrate  pro- 
duced by  the  fermentation  of  citric  acid  juices.  For  the  determina- 
tion of  the  amount  of  insoluble  calcium  salt  obtainable  from  a  citric 
juice,  R.  Warington  recommends  the  following  method  (Jour.  Chem 
Soc.,  1875,  28,  934): — 15  to  20  c.c.  of  unconcentrated  lemon  juice, 
or  about  3  c.c.  of  concentrated  juice  (previously  diluted  to  facili- 
tate exact  measurement)  should  be  exactly  neutralised  with  pure 
sodium  hydroxide.  The  solution  is  brought  to  a  bulk  of  about  50  c.c. 
and  heated  to  boiling  in  a  salt  or  glycerol  bath,  and  so  much  of  a  solu- 
tion of  calcium  chloride  added  as  is  known  to  be  rather  more  than 
equivalent  to  the  total  organic  acids  present.  The  whole  is  boiled  for 
half  an  hour,  and  the  precipitate  then  collected  and  washed  with  hot 
water.  The  nitrate  and  washings  are  concentrated  to  about  10  or  15 
c.c.,  the  solution  being  finally  neutralised  with  a  drop  of  ammonia 
if  it  has  become  acid.  The  second  precipitate  thus  obtained  is 
collected  on  a  very  small  filter,  the  filtrate  being  employed  to  transfer 
it,  and  the  washing  with  hot  water  being  reduced  as  much  as  possible. 
In  very  accurate  experiments  the  concentration  should  be  repeated  and 
any  further  precipitate  collected.  The  precipitates,  with  the  filters, 
are  then  burnt  at  a  low  red  heat,  and  the  neutralising  power  of  the  ash 
ascertained  by  treatment  with  standard  hydrochloric  acid  and  alkali. 
One  c.c.  of  normal  acid  neutralised  corresponds  to  0.070  grm.  of 
crystallised  citric  acid  (C6H8O7,H2O).  The  presence  of  mineral  acids 
does  not  interfere;  oxalic  or  tartaric  acid  would  render  the  results  inac- 
curate. It  is  desirable  to  add  neutral  hydrogen  peroxide  to  the  solu- 
tion of  the  ash  and  boil  before  titrating,  otherwise  an  error  may  occur 
from  the  presence  of  sulphides. 

Official  United  States  Method  for  Citric  Acid  in  Fruit  Juices. 
(Bull.  107,  Bur.  ofCJiew.,  United  States  Depart.  Agriculture,  pageSi). — 


CITRIC   ACID.  563 

50  c.c.  of  the  liquid  are  evaporated  on  the  water-bath  to  a  syrup, 
alcohol  (95%)  added  slowly  and  with  constant  stirring  until  no  more 
precipitation  occurs.  About  80  c.c.  will  generally  be  required.  The 
precipitate  is  collected  on  a  filter  and  washed  with  alcohol  (95%), 
the  alcohol  driven  out  of  the  filtrate  by  evaporation,  the  residue  is 
taken  up  with  a  little  water,  transferred  to  a  cylinder  and  made  up  to 
10  c.c.  5  c.c.  of  this  solution  are  mixed  with  0.5  c.c.  of  glacial  acetic 
acid,  and  then,  drop  by  drop,  a  solution  of  lead  acetate  added.  A 
precipitate  which  dissolves  when  the  liquid  is  heated,  and  reappears 
when  it  is  cooled,  indicates  citric  acid.  If  this  is  present,  the  liquid 
is  heated  to  boiling,  filtered  hot,  the  filter  washed  with  boiling  water  and 
the  filtrates  allowed  to  cool.  The  lead  citrate  that  separates  can  be 
collected  on  a  filter,  washed  with  weak  alcohol,  dried  and  weighed. 
If  tartaric  acid  is  present  its  interference  may  be  prevented  by  adding 
N/io  alkali  in  sufficient  amount  to  neutralise  it  before  adding  the 
alcohol  in  the  beginning  of  the  operation.  Lead  citrate  multiplied  by 
0.483  gives  citric  acid. 

A  method  for  the  analysis  of  calcium  citrate  and  lemon  juice  has  been 
recently  described  by  L.  and  J.  Gadais  (Bull.  Soc.  Chim.  [4],  1909,  5, 
287):  20  grm.  of  the  calcium  citrate  are  boiled  for  a  few  moments  with 
30  c.c.  of  water  and  20  c.c.  of  hydrochloric  acid  (sp.  gr.  1.28),  cooled, 
made  up  to  250  c.c.,  filtered  through  a  dry  filter,  and  25  c.c.  exactly 
neutralised  with  N/i  potassium  hydroxide,  using  phenolphthalein, 
then  treated  with  i  c.c.  of  a  saturated  solution  of  calcium  chloride, 
evaporated  to  25  c.c.,  and  filtered  while  very  hot.  The  precipitate  is 
washed  8  times  with  boiling  water,  using  as  little  as  possible,  and  dried 
at  105°.  The  filtrate  is  concentrated  to  15  c.c.,  any  additional  pre- 
cipitate washed  5  times  with  boiling  water,  sparingly  as  before,  and 
dried  at  105°.  The  filtrate  and  washings  may  be  concentrated  to 
15  c.c.,  and  any  precipitate  treated  as  with  the  other  two.  Finally,  an 
equal  volume  of  alcohol  is  added  to  the  liquid,  and  a  precipitate  is 
added  to  the  others,  after  drying.  The  collected  precipitates  are 
burnt  apart  from  the  filter,  and  the  residue,  calcium  carbonate,  mixed 
with  30  c.c.  of  N/ 1  hydrochloric  acid,  and  the  excess  of  acid  ascertained 
by  means  of  N/i  potassium  hydroxide.  The  c.c.  of  acid  required 
to  neutralise  the  residue,  multiplied  by  0.07  gives  the  amount  of  citric 
acid  that  would  be  obtained  from  the  sample.  If  the  sample  contains 
much  sulphate,  it  is  advisable  to  burn  the  precipitate  over  an  alcohol 
flame,  and  to  add  to  the  residue  10  c.c.  of  hydrogen  peroxide  solution 


564  ACID    DERIVATIVES    OF   ALCOHOLS. 

before  adding  the  acid.  (The  fact  that  commercial  hydrogen  peroxide 
solution  generally  contains  an  appreciable  amount  of  acid  is  not  noted 
in  the  report  of  the  process,  but  must  not  be  overlooked.  The  peroxide 
solution  should  either  be  exactly  neutralized  or  its  acidity  ascertained 
and  allowance  made.) 

For  lemon  juice,  120  c.c.  are  diluted  to  1000  c.c.,  25  c.c.  of  this 
neutralised  with  N/ 1  potassium  hydroxide,  20  c.c.  of  saturated  calcium 
chloride  solution  added,  and  the  procedure  carried  out  as  above. 

In  English-pressed  lemon  juice  the  real  citric  acid  is  99%  of  the 
total  organic  acid,  but  in  the  concentrated  Sicilian  juice  it  ranges  from 
88  to  95%  of  the  total.  In  a  sample  of  concentrated  bergamot  juice, 
Warington  found  the  precipitable  acid  to  be  about  88%  of  the  total 
organic  acid,  but  a  more  usual  proportion  is  96  to  98%.  The  method 
of  determining  the  value  of  juice  by  its  acidity  usually,  but  not  invaria- 
bly, gives  tolerably  accurate  results  in  the  case  of  lemon  and  bergamot 
juice,  but  in  lime  juice  the  results  are  commonly  in  excess  of  the 
truth.  Of  course  this  statement  is  only  true  of  genuine  juice. 

Estimation  of  alcohol  can  be  effected  by  the  usual  methods. 

Adulterated  lime  and  lemon  juices  are  not  uncommon.  The 
production  of  precipitates  with  barium  chloride  and  silver  nitrate  indi- 
cates the  presence  of  sulphuric  and  hydrochloric  acids,  respectively,  pure 
juices  containing  merely  insignificant  traces  of  sulphates  and  chlorides. 
Free  sulphuric  acid  may  also  be  determined  as  in  citric  acid  liquors, 
and  both  that  and  free  hydrochloric  acid  by  Hehner's  method  for  the 
determination  of  mineral  acids  in  vinegar. 

According  to  F.  D.  Scribani  (Jour.  Chem.  Soc.,  1878,  34,  914), 
nitric  acid  has  occasionally  been  used  for  the  adulteration  of  lemon  juice. 
On  concentrating  such  juice  the  nitric  acid  decomposes  the  citric  acidr 
either  wholly  or  partially,  with  formation  of  oxalic,  acetic,  and  carbonic 
acids;  so  that  on  neutralising  the  juice  with  lime  a  mixture  of  calcium 
salts  is  obtained.  To  detect  the  nitric  acid,  Scribani  adds  to  the  juice 
an  aqueous  solution  of  ferrous  chloride,  strongly  acidulated  with  pure 
hydrochloric  acid  and  quite  free  from  ferric  salt.  The  liquid  is  then 
boiled  for  a  few  minutes  and,  after  cooling,  tested  with  a  thiocyanate 
(sulphocyanide).  If  the  liquid  ocontain  nitric  acid,  a  more  or  less 
deep  red  colour  will  be  produced,  owing  to  the  formation  of  a  ferric 
salt.  This  test  is  said  to  answer  equally  well  in  presence  of  common 
salt  or  sulphuric  or  tartaric  acid.  In  boiled  and  dark  coloured  juices 
dilulion  is  necessary  before  the  colour  can  be  observed.  A  more 


CITRATES.  565 

satisfactory  and  direct  test  for  nitric  acid  would  be  to  boil  the  juice 
with  metallic  copper,  when  red  fumes  would  be  produced  if  nitric  acid 
were  present. 

Citrates. — Citric  acid  forms  3  classes  of  salts.  It  has  a  great 
tendency  to  produce  stable  double  citrates,  and  hence  many  metallic 
solutions  are  not  precipitable  by  alkalies  in  presence  of  sufficient  citric 
acid.  This  fact  is  often  utilised  in  analysis. 

No  metallic  citrate  is  wholly  insoluble  in  water.  Calcium  citrate 
is  one  of  the  least  soluble  and  hence  is  employed  in  the  estimation 
of  citric  acid.  General  reactions  of  the  citrates  are  described  else- 
where, and  the  properties  of  the  more  important  commercial  forms 
are  given  below. 

Lithium  Citrate. — As  usually  prepared,  this  a  white  powder,  but 
it  may  be  obtained  in  crystals  with  4  mol.  of  water.  The  salt  is 
generally  stated  to  be  deliquescent,  but  this  is  an  error.  It  should  be 
soluble  without  residue  in  25  parts  of  cold  water. 

The  pure  salt,  after  being  rendered  anhydrous  by  drying  at  115°, 
on  ignition  leaves  52.9%  of  lithium  carbonate.  The  residue  should 
be  treated  with  ammonium  carbonate,  and  again  ignited  very  gently, 
as  it  is  liable  to  lose  carbonic  acid.  A  higher  ash  than  the  above  indi- 
cates impurity  or  adulteration  by  (probably)  sodium  citrate,  which 
leaves  61.5%  on  ignition,  i  grm.  of  anhydrous  lithium  citrate 
leaves  on  ignition  a  residue  which  should  neutralise  at  least  14  c.c.  of 
normal  hydrochloric  acid.  The  same  amount  of  sodium  citrate 
(after  ignition)  would  only  neutralise  11.25  c-c>  °f  acid.  If  the  re- 
sultant solution  be  evaporated  to  dryness,  lithium  chloride  may  be 
dissolved  out  of  the  residue  by  a  mixture  of  equal  volumes  of 
alcohol  and  ether,  while  any  potassium  or  sodium  chloride  will  remain 
undissolved. 

Much  of  the  commercial  lithium  citrate  contains  lithium  carbonate. 
This  gives  it  an  alkaline  reaction  and  increases  its  ash  and  saturating 
capacity.  Excess  of  citric  acid  gives  the  salt  an  acid  reaction  and  re- 
duces the  percentage  of  ash  and  saturating  power.  Hence  these  im- 
purities can  be  distinguished  from  sodium  citrate,  which  raises  the  ash 
and  diminishes  the  saturating  power  of  the  sample. 

Potassium  salts  may  be  detected  by  adding  tartaric  acid  to  the  con- 
centrated solution  of  the  sample  and  stirring,  when  a  white  crystalline 
precipitate  of  acid  potassium  tartrate  will  be  produced. 

Insoluble  matters,  such  as  powdered  petalite  or  lepidolite,  will  be 


566  ACID    DERIVATIVES    OF   ALCOHOLS. 

left  undissolved  on  dissolving  the  sample  in  hot  water,  and  calcium 
compounds  may  be  estimated  in  the  solution  by  adding  ammonium 
oxalate. 

Calcium  Citrate. — This  is  a  white  substance,  very  sparingly  soluble 
in  cold,  and  still  less  in  hot  water.  It  is  produced,  in  an  impure  state, 
by  the  citric  acid  manufacturer  by  boiling  the  juice  with  calcium  car- 
bonate, and  is  offered  in  the  market  as  a  convenient  source  of  citric 
acid.  The  product  consists  essentially  of  citrate  mixed  with  other 
salts  of  calcium,  and  excess  of  lime  or  calcium  carbonate.  In  Sicily, 
dolomitic  lime  is  sometimes  used  for  neutralising  the  juice,  in  which 
case  magnesium  salts  will  be  present.  It  is  particularly  liable  to 
decompose  if  the  percentage  of  moisture  is  considerable  (more  than  10 
or  12%),  and  therefore  some  samples  contain  scarcely  any  real  citrate. 

For  the  analytical  examination  of  commercial  calcium  citrate  it  is 
sufficient  to  estimate  the  citric  acid  and  the  excess  of  carbonate  or 
lime.  For  the  latter  purpose,  5  grm.  of  the  sample  should  be  dissolved 
in  a  known  quantity  of  weak  standard  hydrochloric  acid  kept  gently 
boiling,  and,  when  the  solution  is  quite  cold,  the  amount  of  acid 
neutralised  is  ascertained  by  titration  with  standard  alkali  in  the 
usual  manner.  Each  c.c.  of  normal  acid  neutralised  by  the  sample  cor- 
responds to  0.050  grm.  of  calcium  carbonate  in  the  portion  taken. 
To  determine  the  organic  acids,  2  grm.  of  the  sample  should  be  ignited, 
the  ash  boiled  with  standard  acid,  the  liquid  filtered  and  titrated  with 
alkali.  The  acid  neutralised  by  the  ash  is  due  to  the  calcium  carbonate 
existing  as  such  in  the  sample,  plus  that  produced  by  the  ignition  of  the 
citrate  and  other  organic  salts.  By  substracting  the  neutralisation  due 
to  the  form,  the  equivalent  of  the  organic  acids  is  found;  i  c.c.  of  normal 
acid  neutralised  being  equivalent  to  0.070  grm.  of  monohydrated  citric 
acid.  This  method  gives  all  the  organic  acids  as  citric  acid,  a  result 
which  is  misleading  in  decomposed  citrate.  In  such  samples,  the  real 
citric  acid  should  be  determined  by  dissolving  a  known  weight  in 
hydrochloric  acid,  exactly  neutralising  with  sodium  hydroaide,  and 
treating  the  precipitated  calcium  citrate  as  described  on  page  562. 
Magnesium  citrate  and  citrate  prepared  with  dolomitic  lime  can  be 
correctly  analysed  by  the  titration  method;  but  if  precipitation  be  de- 
sired, the  sample  must  be  decomposed  by  boiling  with  sodium  car- 
bonate, the  magnesium  carbonate  filtered  off,  the  filtrate  neutralised 
with  hydrochloric  acid,  and  precipitated  with  calcium  chloride. 

Ferric   citrate,  may  be  obtained   by  dissolving  ferric  hydroxide 


CITRATES.  567 

in  citric  acid  and  evaporating  the  solution  in  thin  layers.  It  is  thus 
obtained  in  transparent  garnet-red  scales,  which  are  permanent  in  the 
air.  It  is  insoluble  in  alcohol,  but  dissolves  slowly  in  water  to  form 
a  solution  of  a  faintly  ferruginous  taste,  not  precipitated  by  ammonium 
hydroxide,  but  yielding  ferric  hydroxide  on  boiling  with  sodium 
hydroxide.  After  drying  at  100°,  the  scales  should  leave  from  29  to 
30%  of  residue  on  ignition. 

Iron  ammonium  citrate  may  be  made  by  dissolving  precipitated 
ferric  hydroxide  in  a  solution  of  citric  acid  and  adding  ammonia.  It 
occurs  in  thin,  transparent,  deep  red  scales,  slightly  sweetish  and 
astringent.  When  heated  with  potassium  hydroxide  its  solution 
evolves  ammonium  hydroxide  and  deposits  ferric  hydroxide.  The 
alkaline  liquid  filtered  from  the  precipitate  should  not  give  any  crys- 
talline precipitate  or  streaks  of  potassium  hydrogen  tartrate,  when 
acidulated  with  acetic  acid  and  vigorously  stirred.  Ferric  ammonium 
citrate  is  readily  soluble  in  water,  forming  a  faintly  acid  solution,  but  is 
almost  insoluble  in  95%  alcohol. 


APPENDIX. 


The  detection  of  lead  is  materially  influenced  by  the  presence  of  iron. 
Freshly  precipitated  ferric  hydroxide  will,  by  adsorption,  carry  down 
lead  hydroxide.  The  procedure  under  such  conditions  has  been 
recently  investigated  by  J.  M.  Wilkie  (J.Soc.  Chem.  Ind.,  1909,  28, 
637)  who  finds  that  the  usual  method  of  preventing  precipitation  of 
iron  by  adding  potassium  cyanide  succeeds  only  when  the  iron  is  in 
the  ferrous  state.  As  a  result  of  many  experiments,  Wilkie  gives  a 
special  process.  He  uses  sodium  sulphide  as  the  final  precipitant, 
but  W.  A.  Davis  prefers  freshly-made  colourless  ammonium  sulphide, 
prepared  by  diluting  2  c.c.  of  0.880  ammonia  to  10  c.c.  and  saturating 
with  well-washed  hydrogen  sulphide.  Standard  lead  solutions  may  be 
conveniently  made  from  a  strong  solution  of  pure  lead  (5  grm.  in 
nitric  acid,  evaporated  to  remove  all  but  a  small  amount  of  the  acid 
and  made  up  to  1000  c.c.  This  strong  solution  keeps  fairly  well. 
For  use  portions  of  it  are  diluted  100  times  and  applied  in  the  usual 
manner  for  colour  comparisons. 

Tartaric  Acid. — Dissolve  10  grm.  of  the  acid  in  about  25  c.c.  of  hot 
water,  cool,  add  2  c.c.  of  N/io  sodium  thiosulphate,  heat  to  incipient 
boiling,  cool,  add  i  c.c.  of  10  per  cent,  potassium  cyanide  and  then 
ammonia  (0.880)  in  small  portions  until  the  solution  smells  faintly  of 
the  reagent.  Boil  until  the  liquid  is  colourless,  pour  into  a  tall 
cylinder,  make  up  to  100  c.c.,  and  add  2  drops  of  freshly-prepared 
colourless  ammonium  sulphide. 

The  tint  developed  is  compared  with  tints  produced  by  solutions 
made  from  absolutely  lead-free  acid  to  which  known  amounts  of  lead 
have  been  added,  so  as  to  give  comparisons  at  say  5  parts  per  1,000,000, 
10  per  1,000,000,  etc. 

Cream  of  tartar  should  be  tested  by  dissolving  10  grm.  of  the  sample 
in  hydrochloric  acid,  adding  sodium  thiosulphate  and  proceeding  as 
above  directed. 

Owing  to  the  wide  distribution  of  lead,  care  must  be  taken  that  all 
the  reagents  are  free  from  it. 


INDEX. 


ABSORPTION  spectra,  33 
Acacia,  gum,  440 
Acetal,  268 

—  dimethyl,  268 
Acetaldehyde,  264 
Acetate  of  iron,  511 

lime,  507 

Acetates,  488,  506 
Acetic  acid,  488 

—  assay  of,  490 

—  glacial,  494 

—  homologues  of,  514 
Acetic  aldehyde,  264 

—  ether,  236 
Acetone,  104 

—  in  urine,  106,  108 

—  in  wood  spirit,  100 
Acid  mercuric  iodide,  368 

—  nitrate,  368 
Acids,  vegetable,  485 
Adracanthin,  444 
Agar-agar,  437 
Alcohol,  no 

—  absolute,  no 
denatured,  113 

—  detection  of,  114 

estimation  of,  115 

in  essences,  129,  130 

in  fusel  oil,  130 

—  in  tinctures,  129,  130 

—  methyl  compounds  in,  95 

—  specific  gravity  of,  115 
ethyl,  no 

methyl,  85 

Alcohols,  85 
Aldehyde,  253 

—  acetic,  264 

acrylic,  235 

formic,  256 

resin,  254 

trichlor-,  268 

valeric,  252 

Aldehydes,  253 

Ale,  149 

Allylene  dichloride,  273 

Alum  in  bread,  459 

—  in  flour,  457 


Alumina  cream,  309 
Aluminum  acetate,  510 
Amyl  acetate,  249 
alcohol,  130 

—  nitrate,  252 

—  nitrite,  250 
Amylan,  406 
Amylin,  427 

A.  O.  A.  C.,  285 
Arabic  acid,  440 

—  gum,  440 
Arabin,  444 
Arabinose,  287,  400 
Argol,  542 
Arrowroot,  417 
Arsenic,  detection  of,  63 

estimation  of,  146 

Artifical  fruit  flavors,  235 
Ash,  estimation  of,  71 
Attenuation,  151 


BALLING'S  hydrometer,  291 
Bamboo  fibre,  481 
Barley,  142,  463 

sugar,  339 

Bananas,  463 
Barfoed's  reagent,  333 
Basic  lead  acetate,  308 
Bassorin,  444 
Bate's  saccharometer,  291 
Baume's  hydrometer,  15 
Beer,  149 

—  bitters  in,  161 

carbon  dioxide  in,  157 

extract  in,  156 

—  preservatives  in,  163 

—  stability  of,  164 

Beer- wo  it,  orginal  gravity  of,  151 

—  maltose  and  dextrin  on,  141 
Beet  products,  359 

root,  composition  of,  360 

—  juice,  359 

molasses,  357 

sugar,  360 

Benedict's  reagent,  395 
Bergamot  juice,  559 


571 


.572 


INDEX. 


Bi- rotation,  315 

Bitters  in  beer,  161 

Black  liquor,  511 

Boiling  point,  17 

Brandy,  200 

Bread,  418 

Breakfast  foods,  464 

Brewing  sugar,  379 

British  gum,  427 

Brix  hydrometer,  291 

Bromine  in  organic  substances,  62 

Bromoform,  281 

Butyl  alcohol,  187 

chloral,  273 

Butyrate,  523 
Butyric  acid,  521 
—  chloral,  273 


Citric  acid,  detection  of,  487,  555 

estimation  of,  555 

liquors,  558 

Claret,  186 

Cleyet's  formula,  313 

Cologne  spirit,  112 

Colonial  spirit,  88 

Columbian  spirit,  88 

Compound  ethers,  231 

Confectionery  sugar,  358 

Copper  acetate,  513 

Cotton  fibre,  481 

Cream  of  tartar,  543 

Croton  chloral,  273 

Crude  fibre,  estimation  of,  70 

Cutocellulose,  434 

Cutose,  434 


CALCIUM  acetate,  507 

citrate,  566 

tartrate,  548 

Candy,  338,  358 

Cane  products,  359 

Cane  sugar,  288,  301,  313,  338 

detection  of,  341 

estimation  of,  342 

inversion  of,  290 

Caramel  in  wine,  179 
Carbinol,  85 
Carbohydrates,  285 
Carbon  dioxide  in  beer,  157 
Cartier's  hydrometer,  15 
Cellulose,  406,  429 

estimation  of,  437 

purification  of,  435 

Cereals,  450 

—  composition  of,  450 

mineral  matters  in,  456 

proteins  in,  412 

Chloral,  269 

alcoholate,  269 

butyl,  273 

—  detection  of,  271 

—  estimation  of,  271 
formamide,  274 

hydrate,  269 

—  meta-,  268 
Chlorethylene,  248 

Chlorine  in  organic  substance,  62 
Chloroform,  274 
commercial,  276 

—  detection  of,  274 

—  estimation  of,  274 
methylated,  276 

spirit  of,  280 

Cider,  187 
Citrates,  555,  565 
Citric  acid,  555 


DENATURED  alcohol,  113 
Dephlegmators,  21 
Dextrin,  427 

apparent,  141 

in  beer,  150 

Dextro-glucose,  287 
Dextrose,  287,  301,  372 

—  estimation,  325 
Diastase,  preparation  of,  421 
Diastatic  power  of  malt,  136 
Dichlormethane,  281 
Dimethylacetal,  268 
Disaccharides,  286 
Dispersion,  22 
Distillation,  18 

fractional,  18 

Dutch  liquid,  248 


EBULLIOSCOPE,  127 
Erythrodextrin,  428 
Esparto  fibre,  481 
Essences,  alcohol  in,  130 

artificial,  235 

Esters,  231 

in  spirits,  195 

—  in  wood  naphtha,  101 
Ether,  227 

acetic,  236 

commercial,  228 

methylated,  23 1 

methyl,  231 

nitrous,  241 

spirit  of,  241 

spirit  of,  23 1 

Ethers,  compound,  231 
Ethyl  acetate,  236 

alcohol,  no 

bromide,  248 

carbamate,  248 


Ethyl  chloride,  247 
chlorinated,  248 

—  dithiocarbonates,  240 
ether,  227 

nitrite,  241 

oxide,  227 

sulphate,  239 

—  sulphuric  acid,  240 

—  thiocarbonates,  240 
Ethylene  dichloride,  277 
Ethylidene  chloride,  248 
Extract  in  beer,  157 
in  wine,  168 

malt,  145 


FEELING'S  solution,  318 
Fermentation,  acetic,  488 

alcoholic,  223,  298 

Fibre,  crude,  70 
Fibres,  vegetable,  418 
Finish,  methylated,  114 
Flax  fibre,  481 
Flour,  453 

gluten  in,  455 

Fluorescence,  40 
Formaldehyde,  250 

methyl  alcohol  in,  93 

Formalin,  257 
Formates,  520 
Formic  acid,  519 
Fractional  distillation,  18 
Fruit  essences,  235 
Furfural,  196 
Fusel  oil,  187 

alcohol  in,  130 

in  spirits,  188 


GALACTOSE,  287,  376 
Gin,  203 
Gliadin,  455 
Gloy,  429 
Glucose,  287,  372 

laevo-,  287,  373 

syrup,  377 

Glucoside,  391 
Glucuronic  aldehyde,  399 

acid,  399 

Gluten,  455 
Glutenin,  455 
Glycerol  in  wine,  *+f^ 
Glycogen,  406 
Grain,  raw,  144 
Grape  sugar,  377 
Grits,  144 
Gum  acacia,  440 

—  arabic,  440 

—  tragacanth,  444 


INDEX. 

Gums,  406,  438 


HEMP  fibre,  481 
Hexamethylene-amine,  263 
Higher  alcohols,  187 
High  wines,  112 
Honey,  384 
Hop  resin,  161 

substitutes,  161 

Hydrochloric  ether,  247 
Hydrometers,  7 
Hydrolysis,  296 


IMMISCIBLE  solvents,  79 

Inversion,  296 

Invertase,  314 

Invert  sugar,  289,  329,  375,  385 

Iodine  in  organic  substances,  62 

lodoform,  282 

Iron  acetate,  511 

liquor,  511 

Isobutyl  alcohol,  194 
Isobutyric  acid,  523 
Isomaltose,  379 
Isovaleric  acid,  524 


JUTE  fibre,  433 


KJELDAHL- ARNOLD  method,  62 

Gunning  method,  59 

Knapp's  solution,  337 
Kcettstorfer  method,  232 


LACTOSE,  288,  301,  365 

Laeonlose,  401 

Laevulose,  287,  301 

Lead  in  citric  acid,  557,  569 

—  in  tartaric  acid,  549,  569 
Lees,  542,  546 
Lemon  juice,  559 
Lignin,  433 
Lignocellulose,  433 
Lime  juice,  559 
Linen  fibre,  481 
Lintner  value,  136 
Low  wines,  495 


MAIZE,  462,  463 
Malates,  534 
Malic  acid,  533 
Malt,  133 

diastatic  value  of,  136 

—  extract,  145 


573 


574 


INDEX. 


Malt,  liquors,  133,  149 

—  substitutes,  143 

—  sugar,  141,  361 

—  wort,  135,  140 
Maltose,  288,  301,  361 

—  apparent,  141 
Manila  hemp  fibre,  481 
Mannose,  287 

Maple  sugar,  388 

syrup,  388 

Massacuites,  344 
Melibiose,  288 
Melting  point,  16 
Mercuric  iodide  solution,  368 

nitrate  solution,  368 

Mesotartaric  acid,  533 

Metals  in  organic  substances,  63,  75 

Metachloral,  268 

Methaldehyde,  250 

Methyl  alcohol,  85 

carbinol,  no 

ether,  23 1 

Methylated  chloroform,  277 

ether,  23 1 

finish,  114 

—  spirit,  95,  104 
Milk  sugar,  288,  301,  365 
Moisture,  estimation  of,  64 
Molasses,  344,  355 
Monochromatic,  43 
Monosaccharides,  286,  372 
Mucic  acid,  376 
Mucocellulose,  434 
Mucilages,  434 
Mutarotation,  315 

Nitre,  spirit  of,  242 
Nitrogen,  estimation  of,  58 
Nitroethane,  243 
Nitropentane,  252 
Nitrous  ether,  241 

—  spirit  of,  242 

OATS,  463 

(Enolin,  181 

Optical  properties,  22 

Orange  juice,  401 

Original  gravity  of  worts,  151 

Ovens,  drying,  66,  69 

Oxalates,  528 

Oxalic  acid,  527 

Oxycellulose,  531 

PAPER,  465 

—  fibres,  474 

—  testing,  466 
Paraform,  256 
Paraldehyde,  267 


Parchment  paper,  431 
Pavy's  solution,  331 
Pectates,  434 
Pectic  acids,  434 
Pectocellulose,  434 
Pectose,  434 
Pentoses,  400 
Pentyl  acetate,  249 

alcohol,  187 

Perry,  125 

Pith,  429 

Plants,  proximate  analysis  of,  445 

Polarimeters,  41 

Polarisation,  41,  310 

Polysaccharids,  286,  405 

Porter,  149 

Potable  spirits,  187 

Potato  spirit,  187 

Potatoes,  assay  of,  426 

Pot-still  whisky,  202 

Preservatives  in  beer.  163 

in  wine,  175 

Proof  spirit,  111 

vinegar,  496 

Propionic  acid,  522 
Propyl  alcohol,  187 
Proteins  in  cereals,  452 
Proximate  analysis  of  plants,  445 
Pyridine  in  wood  spirit,  102 
Pyrolignite  of  iron,  511 

of  lead,  512 

of  lime,  507 

Pulp,  paper,  418 

QUASSIA  in  beer,  161 

RACEMIC  acid,  536,  541 
Raffinose,  288 
Raw  grain,  144 
—  sugar,  351 
Rectified  spirit,  in 
Red  liquor,  510 
Refractometers,  22 
Rhamnose,  403 
Rice,  454 
Rochelle  salt,  552 
Rum,  203 
Rye,  463 


SACCHARIMETRY,  305 
Saccharin,  164,  175 
Saccharine  solutions,  289 
Saccharometry,  291 
Saccharum,  375 
Sachsse's  solution,  337 
Salicylic  acid  in  beer,  163 
in  wine,  175 


••nil 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN     INITIAL    FINE     OF     25     CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  5O  CENTS  ON  THE  FOURTH 
DAY  AND  TO  Sl.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


NOV   30  1932 
DEC    1 


6 


18  1933 


28 


1938 


NOV   221938 
JAN  29  1945 

MAR 


LD  21-50m-8,-32 


Coinmerc 
:anlc 


Mar.  17, 194 17 


al 

analvs  is . 


_1_909 

v 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


